# 250 years of Tintinnid Studies: Pioneers of Tintinnid Studies

John R Dolan

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John R Dolan. 250 years of Tintinnid Studies: Pioneers of Tintinnid Studies. Acta Protozoologica, 2026, 65 (1), pp.1-25. 10.4467/16890027AP.26.001.23171. hal-05526290

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# 250 years of Tintinnid Studies: Pioneers of Tintinnid Studies

John R. DOLAN

Laboratoire d'Océanographie de Villefranche-sur-Mer, CNRS-Sorbonne Université UMR7093, Institut de la Mer de Villefranche, IMEV, 181, Chemin du Lazaret, 06230, Villefranche-sur-Mer, France

**Abstract.** The first tintinnid ciliate was discovered and described in 1776, using just five words. Although now 250 years old, the study of tintinnids is still a very active field. According to Google Scholar, in the last 10 years, 151 works have appeared with the term "tintinnid" in the title. Early works mostly concerned species descriptions. In contrast, the recent studies have focused on a wide variety of topics: ecology, phylogeny, physiology, behavior, and biogeography. Here the beginnings of the long and rich history of tintinnid studies are traced through the stories of early workers in the period from the first descriptions, up to and including the appearance in 1929 of Kofoid and Campbell's landmark treatise and its revision in 1939. Many are unaware of the fact that early protistologists who worked on tintinnids were prestigious biologists of their time, now known as important contributors not only to our knowledge of tintinnids, but also other groups of protists. There were ardent defenders of Darwin among the early workers. There were also often interesting interconnections between the early workers, while some began studying tintinnids almost by accident. A companion paper will shine a light on modern workers of tintinnid studies.

**Keywords:** history of protistology, ciliates, plankton, Tintinnina, microzooplankton

## INTRODUCTION

The study of tintinnid ciliates began quite discretely in Frederich Otto Müller's 1776 *Zoologiea Danicae Prodromus*. The *Prodomus* (or Prologue) was published as a pre-cursor or prospectus for his major work in progress, the large format, multi-volume, *Zoologica Danica* that would consist of detailed descriptions of all the animals of Denmark and Norway and many illustrations. In contrast, the *Prodomus* was a slim volume (20 cm tall), of about 300 pages. It was a simple

catalogue of animal species, over 3000, with very brief text descriptions, and contained many new species. The start of tintinnid studies was discrete in the *Prodomus* because the first text on a tintinnid was but 5 words in the few pages of an "Addenda" of Müller's *Prodomus*. Some are likely unaware of the humble beginning as the Addenda is actually missing in some digitized copies of the work available today (e.g., from the University of Michigan Library, and the National Library of Austria). Müller's 1776 tintinnid description was the five words: "follico cylindrico hyalino, pedicello retortili" (cylindrical hyaline shell, with a twisted pedicel). He gave it the name *Trichoda inquilinus* (*inquilinus* = lodger or inhabitant), and it was one of many species in his genus *Trichoda*, a quite heterogenous group known at the time as part of the 'infusoria'. They acquired the term infusoria because they were the microorganisms

<footnote>Address for correspondence: John Dolan, Laboratoire d'Océanographie de Villefranche-sur-Mer, CNRS-Sorbonne Université UMR7093, Institut de la Mer de Villefranche, IMEV, 181, Chemin du Lazaret, 06230 Villefranche-sur-Mer, France ; E-mail: john.dolan@imev-mer.fr</footnote>
found in infusions of vegetable matter by the early mi-
croscopists. No longer lost among the ‘infusorsia’, tin-
tinnids are now recognized as an important part of the
marine plankton, and thus marine food webs. It is per-
haps worth mentioning that studies of tintinnids, with
a 250-year history, began far before the voyage of the
Challenger Expedition (1872–1876), often taken to be
beginning of Oceanography (e.g. Schlee 1973), as well
as the coining of the term ‘plankton’ by Victor Hensen
in 1887 (Dolan 2021a).

But to return to the distant past, for well over
50 years, *Trichoda inquilinus* would be the only known
tintinnid, and Müller the only person known to have
seen it. Nonetheless, the species was renamed twice by
people who had not actually seen it. First by Franz von
Paula Shrank, who proposed the genus name *Tintin-
nus* for three of Müller’s *Trichoda* species with shells,
thus it became *Tintinnus inquilinus* without mention of
the etymology of word ‘tintinnus’ (Schrank 1803), and
then by Jean-Baptist Lamarck, who proposed including
it among the folliculinide ciliates as *Vaginicola inqui-
lina* (Lamarck 1816). It was not until 1833 that Chris-
tian Gottfried Ehrenberg saw it again in waters from
Kiel and later in Copenhagen, where Müller had found
it. Ehrenberg published a re-description of it based on
his own observations in 1835 and he retained the name
Shrank gave it. Ehrenberg published his illustrations of
it in his first monographic work *Die Infusionsthierchen
als vollkommene Organismen. Ein Blick in das tiefere
organische Leben der Natur* (Ehrenberg 1838). Soon
after, it was found by Félix Dujardin in the Mediterra-
nean Sea and given again Lamarck’s name *Vaginicola
inquilina* in Dujardin’s monograph (Dujardin 1841). It
was next reported in 1844 as *Tintinnus inquilinus* seen
near St. Petersburg (Eichwald 1844). These were the
beginnings of the rather complicated taxonomic his-
tory of Müller’s *Trichoda inquilinus*. It was reviewed
at length in 1929 by Kofoid and Campbell in their *Con-
spectus of the Marine and Freshwater Ciliata Belong-
ing to the Suborder Tintinnoinea*… (Kofoid and Camp-
bell 1929). Their *Conspectus* and their follow-up 1939
*The Ciliata: The Tintinnoinea* mark the end of the era of
pioneer studies. They catalogued, and often re-named,
the known forms of tintinnids, numbering by then over
400 and they added over 200 more. Thus by 1940 there
were about 700 known species, representing the major-
ity of the approximately 800 forms of tintinnids today
recognized as distinct species. A graph showing species
accumulation with time, with points identifying the

appearance of key early publications concerning tintin-
nids, is shown in Fig. 2.

The stories of the workers who produced the early
key publications, and their contributions to our knowl-
edge of tintinnids, constitutes the first part of the history
of tintinnid studies, and is presented here as ‘Pioneers of
Tintinnid Studies’. Unknown to most of us, there were
often interconnections between the early investigators,
while others appear to have taken up tintinnid studies
by accident. A companion work, in progress, ‘Modern
Era Workers’. constitutes the second part of the history
of tintinnid studies. It will consists of thumbnail sketch-
es of modern-era workers, those following the appear-
ance Kofoid and Campbell’s first monograph (Kofoid
and Campbell 1929), who have made significant con-
tributions to our knowledge of tintinnids. The remark-
able diversity of workers and approaches involved in
the study of tintinnids in modern era will be shown.
Evidence of the continuing variety and quantity of cur-
rent research focusing on tintinnids in recent years is
furnished in the supplementary file listing the full refer-
ences to the 151 publications on tintinnids published in
the last ten years (2016–2025).

OTTO FRIEDRICH MÜLLER (1730–1784)

The discovery of tintinnids, as well as a large num-
ber of other protists, is credited to Otto Friedrich Müller.
He was the most important Danish naturalist of his
time, and a contemporary of Linnaeus. The following
brief account of his life and works is based on those of
Anker (1950) and Spärck (1932). As were most natural-
ists of his time, Müller was largely self-educated with
regard to subjects of natural history. His only formal
studies were in theology and later the law. He then
worked as a tutor and his first works were on the in-
sects of Frederiksdal where he was a tutor, and then on
the plants of Frederiksdal. Müller only began devoting
himself entirely to studies of natural history after his
marriage to a wealthy widow gave him financial inde-
pendence for the last 17 years of his life. His first major
publications were his volumes in the series *Flora Dan-
ica*. Müller then turned his attention to microorganisms
and invertebrates. In 1773–1774 he published a two
volume work (without illustrations) on terrestrial and
freshwater forms: “Vermivm terrestrium et fluviatilium,
seu, Animalium infusoriorum, helminthicorum et testa-
ceorum, non marinorum, succincta historia.” One of
<figure><img src="image_2.png" /><figcaption>Fig. 1. Left panel: the cover page of Müller's 1776 *Zoologiæ Danicæ Prodomus*. Right panel: page 281, one of the eight pages of the "Ad-denda" in which the first description of a tintinnid appeared in the section "Inquirenda et Corrigenda." *Trichoda inquilinus* was described with the five words "follico cylindrico hyalino, pedicello retortili." The asterisk denoted it as a new species, that is one not in any of the publications of Linnaeus, and the cross as a name given it by Müller (Anker 1950). The last line reading "Zool. dan. T. IX, f. 2" indicated that an illustration of it will be shown in plate 9, fig. 2 of the *Zoologica Danica*.</figcaption></figure>

his last works was his major contribution, *Zoologica Danica*. Müller though only lived to see the publication of the first volume as he died at the age of 54 in 1784. His key publication with regard to protists is often considered to be his *Animula Infusoria Fluvia et Marina...* (Cole 1926; Corliss 1978). It appeared posthumously in 1786 and included a short text on *Trichoda inquilinus*.

However, little appreciated is that Müller also published substantial articles on protists, one on reproduction in 'infusoria' (Müller 1783a) and another on the culturing of 'infusoria', published posthumously (Müller 1788).

As noted above, Müller's *Zoologicæ Danicæ Prodomus* with the first mention of a tintinnid, was a prologue and prospectus of his key production, *Zoologica*
<figure><img src="image_3.png" /><figcaption>**Fig. 2.** The cumulative number of forms of tintinnids described, as a function of time, showing the temporal increases in the number described forms from 1776 to 2025. The graph is a revised and updated version of that appearing as fig. 3.1 in Agatha and Strüder-Kypke (2013). The points in time corresponding to the appearances of works of the pioneers in tintinnid studies presented here are noted. Many of the forms, originally described as varieties or forms of other species, are today recognized as distinct species, were raised to species status in the works by Kofoid and Campbell (1929, 1939). Note that the formal description of new forms of tintinnids has nearly come to a halt in recent years.</figcaption></figure>

*Danica*. This later work included the first detailed description, and multiple illustrations of a tintinnid. According to Akner's account of the production of *Zoologica Danica*, its publication history is exceedingly complicated (Anker 1950). Originally, all of the volumes were to have text descriptions in Latin, Danish and German. The first volume to be published was to include both the description and illustrations of *Trichoda inquilinus* (as indicated in the description of *T. inquilinus* in the *Prodomus*). However, the plates for volume one were published without the text in 1777, perhaps to spark interest in work. The first complete edition of volume one appeared in 1779; it had short texts in Latin only and the plates. An edition with the plates and longer texts in Danish appeared in 1781, and yet another edition of volume one with the longer text of descriptions resembling those of the Danish edition, but in German, appeared in 1783 (Müller 1783b). Thus, between the *Prodomus*, the editions of the *Zoologica*

*Danica*, and the *Animula Infusoria*, there are four text descriptions of various lengths concerning *T. inquilinus* credited to Müller. By far, the most poetic are the long texts in the Danish and German language editions of *Zoologica Danica*. Below is a translation of the first paragraph of Müller's text in the German edition of *Zoologica Danica* (Müller 1783, pg. 31), revealing his feelings in observing the first tintinnid (translated using Google Translate).

"The sensations that the first sight of an organic body in the animal or human kingdom awakens are almost as varied as its different forms. Astonishment, wonder, tranquility, pleasure, smiles, joy, with their manifold shades, appear on the face of the beholder; he would gladly express each and every one in words, but here all languages are impoverished. That it is strange, astonishing, beautiful, lovely, unexpected- these are only faint rays of the uplifting light that surprises the soul. But we leave this vast field to the observer of
<figure><img src="image_4.png" /></figure>

**Fig. 3.** The left panel is fig. 2 of plate 9 in the first volume of *Zoologica Danica*. The right panel is a portrait of O. F. Müller in 1776 at age 46, when he began work on the *Zoologica Danica*. Müller's legend for depictions of *Trichoda inquilinis* from the last description published in the 1786 *Animalcula Infusoria Fluviatilla et Marina* reads (using Google Translate): "Plate IX. fig. 2. show this *Trichoda* in a different ways; and indeed in the first series the first figure shows the animalcule in the extremity of the follicle with a crater-shaped open capitulum, but without cilia, and an extended peduncle; the second and fourth figures barely indicate a lateral halo, but a twisted peduncle; the third animalcule is retracted with a very shortened peduncle, with no cilia; the fourth is likewise retracted, with a visible halo, but with no peduncle, and the Monads occupying the margin of the follicle; in the second series the bottom, second and third figures show pregnant animals, with no cilia showing in the first, and the two remaining ciliated ones visibly; in the second the animalcule is sessile; which the mother has already divided into two with the upper one ciliated together, both living within a common follicle."

the human soul, and turn to the creature whose first
sight filled me with new admiration and captured my
entire affection."

Fig. 3 shows the Illustrations of *Trichoda inquilinus*
which appeared in figure 2 of plate 9 of *Zoologica
Danica*, as noted in the brief description of the *Prodomus*.
The drawings for the plate were made by Müller's brother Christian Friderich Müller (1774–1814), with whom he worked closely making microscopical observations (Anker 1950). In Müller's descriptions he stated that he had seen it in samples of seawater from the harbor of Copenhagen, in winters of 1776–1778.

CHRISTIAN GOTTFRIED EHRENBERG
(1795–1876)

The second person to have reported seeing tintinnids, and also to have published illustrations of them, was Christian Gottfried Ehrenberg. He was a major figure of 19th century biology and made important contributions to many fields, including pioneer studies of other group protists such as radiolaria (Lazarus 2014)

and foraminifera (Jones 1877). The following summary
focusing on his work on microorganisms, is based on
the account in Dolan (2022a), and references therein.
Here the titles of his works are given in English; the
original German titles are given in References. Ehren-
berg first trained as botanist, and his well-received
thesis on the mushrooms of the forests of Berlin, gave
him some renown as an expert on fungi. He then, as
a botanist, with his friend Wilhelm Friedrich Hemp-
rich, as a zoologist, undertook an expedition of explo-
ration and collecting in North Africa and the Middle
East. It was an epic journey, followed by the press at the
time. They left Berlin in 1820, and Ehrenberg returned
as one of the few survivors in 1825. Work done dur-
ing the expedition was the basis for Ehrenberg's first
work on microorganisms, "The geographical distribu-
tion of the infusion animals in North Africa and West
Asia, observed on Hemprich and Ehrenberg's travels."
He read it in 1828 to the Imperial Academy of Scienc-
es (Ehrenberg 1832a). Soon after, Ehrenberg was re-
cruited to participate, as a zoologist, by Alexander von
Humboldt to join him in his expedition to Siberia in
1829. Just a few months after his return to Berlin, he
read to the Academy another study on microorganisms,
<figure><img src="image_5.png" /><figcaption>**Fig. 4.** The right panel shows Ehrenberg's illustrations of tintinnids in plate 30 of his 1838 *Die Infusion Organisms as Complete Organisms. A Glimpse into the Deeper Organic Life of Nature*. The illustrations labeled ‘II’ are *Tintinnus inquilinus*, shown both attached to algae (1 & 2), as he found in samples sent to him from Kiel, and free-swimming (3–5), in samples from Copenhagen, in water scooped up from the harbor. The illustrations labeled ‘III’ are *Tintinnus subulatus*, with a ciliate cell inside (1 & 3) and an empty lorica (2). The left panel is a portrait of Ehrenberg in 1847, at age 52.</figcaption></figure>

"Contributions to the knowledge of the infusoria and their geographical distribution, especially in Siberia" (Ehrenberg 1832b). The study brought Ehrenberg considerable fame. Translations and summaries appeared in English and French that included Ehrenberg's claim that some infusoria had distinct organs, like those of multi-cellular organisms, such as the multiple stomachs of his 'polygastrica', which eventually brought him into some disrepute (see Dolan 2022a).

Ehrenberg's contributions to our knowledge of tintinnids, as noted above, included the first observations of Müller's *Trichoda inquilinus* since Müller's own in 1776. It was 57 years later, in 1833, that Ehrenberg again found *T. inquilinus* and in 1835 described it as *Tintinnus inquilinus*, found in seawater samples, first from Kiel, and then again in samples from Copenhagen. Ehrenberg also found and described as *Tintinnus subulatus*, a second tintinnid species, in seawater samples from Kiel in 1835. Ehrenberg's re-description of Müller's *Trichoda inquilinus* and his new tintinnid species, *Tintinnus subulatus*, appeared but without illustrations, in his massive 1835 article in which the two tintinnid species could be easily over-looked. The article of 222 pages and 11 plates contained the descriptions of 135 species, with the vast majority described as new species (Ehrenberg 1835).

A few years later, Ehrenberg did include illustrations of *Tintinnus inquilinus* and *T. subulatus* in his 1838 landmark monograph *Infusion Organisms as Complete*

*Organisms. A Glimpse into the Deeper Organic Life of Nature* (Ehrenberg 1838). At the time it was very well received. A review in the *Magazine of Natural History* by Weimar (1939) began with the sentences: "This work, which may truly be looked upon as marking an epoch in Natural History, contains on 133 printed sheets the results which the most skillful and successful observer with the microscope has obtained during many years of laborious and persevering research, in different parts of the globe. It may be said that the microscope has become, in the hands of Prof. Ehrenberg, a means of information not less important than the telescope..." In more recent years it has been called "the most sumptuously illustrated classic of the field" (Churchill 1989). Ehrenberg's illustrations of *T. inquilinus* and *T. subulata* from the 30th of the 64 plates are shown in Fig. 4. To Ehrenberg's monograph, we owe not only the first illustrations of tintinnids since Müller, but also the clear explanation of the term *tintinnus* (Latin for sounder or bell) with regard to tintinnids. In Ehrenberg's description of the genus *Tintinnus*, he stated "...in the interior of the shell, the body has a flexible pedicel (similiar to the clapper of a bell)." It is perhaps worth noting that while the cell and pedicel of *Tintinnus inquilinus* was likened to a bell clapper attached to a rope, the tubular lorica was not likened to a bell. A couple years later, Ehrenberg added two new species to the genus *Tintinnus* as *T. campanula*, now known as *Tintinnopsis campanula*, and *T. denticulata*, now known as *Parafavella*
*denticulata* (Ehrenberg 1840). In Ehrenberg’s last work that included new tintinnid species, he erected a new genus, *Dictyocysta* with two species, *D. elegans*, and *D. lepida* (Ehrenberg 1854a). He provided no illustrations but did mention that one of his new species, *D. elegans*, was apparently seen by Johannes Müller as it appeared in one of the plates of Müller’s 1843 publication on the feather starfish, *Pentacrinus caputmedusa*. The plate showed the remains of prey items in the alimentary canal. Johannes Müller and his novel discovery are portrayed as the next ‘pioneer’. However, Ehrenberg did eventually publish an illustration of his *D. elegans* in his second classic monograph *Microgeology* (Ehrenberg 1854b). It appears in plate 54 (as ‘D’, bottom near center) but it looks much more like *D. mitra* than *D. elegans*!

Among the hundreds of species named for Ehrenberg, likely the best known to tintinnid workers today is *Favella ehrenbergi*, originally named for him as *Tintinnus ehrenbergi* by Claparède and Lackmann (1858).

## JOHANNES MÜLLER (1801–1858)

Johannes Müller did not work on tintinnids. However, he is given attention here as an important personality, and key influence, in the lives of those who made quite important contributions to our knowledge of tintinnids. Furthermore, in his 1843 publication, Müller’s documentation of a tintinnid lorica, among the remains of microscope organisms in the alimentary canal of a suspension-feeding feather starfish (see Fig. 5), the finding noted by Ehrenberg mentioned above, is

actually quite significant. It appears to be oldest piece of evidence showing that tintinnids (and other protists of the marine plankton) are fed upon by a very wide variety of organisms, including benthic animals. Presented here then is a brief account of Müller’s life based on those of Otis (2007) and Zeller and Werneburg (2024).

Johannes Müller was born in 1801 and his father expected him to take over the family business of his leather workshop making saddles and shoes. However, at the age of 14, the director of the secondary school convinced his father that he excelled at languages and mathematics and should be given a university education. In 1819 Müller entered Bonn University, at first to study theology, but quickly switched to medicine. As a student, he published a paper in 1822 on the laws of physics governing motion in lower animals (Müller 1822). It was the first of 267 works he authored by the time of his death in 1858 at the age of 57. Müller’s first academic position was as a lecturer at the Bonn University in 1824 and he quickly moved through the ranks. He was made Associate Professor in 1826, and Professor in 1830. He took the position of Professor of Medicine and Physiology at the prestigious Berlin University in 1833 at the age of 32, and soon became the premier anatomist and physiologist in the German states. Some of his students in 1830’s and 1840’s include the now well-known figures Theodor Schwann, Emil du Bois-Reymond, and Hermann von Helmholtz. It was in the 1850’s, that three future protistologists met and became close friends while studying under Müller. They were Édouard Claparède, Johannes Lackmann, and Ernst Haeckel who all went on to make remarkable

<figure><img src="image_6.png" /><figcaption>**Fig. 5.** The left panel shows the figures 4–9 from plate 6 of Müller’s article on the anatomy of the feather starfish *Pentacrinus caputmedusa* (Müller 1843). The figures depict the microscopic remains he found in the alimentary canal, identifiable as diatoms (fig. 4 & 5), a lorica of the tintinnid now known as *Dictyocysta mülleri* named for him by Jörgensen in 1924 (fig. 6), and a dinoflagellate (fig. 7). The right panel shows a formal portrait of Müller from about 1850, and shows his interest in echinoderms as his hand clutches a sea urchin shell, and on the table, is a bottled specimen of a feather starfish, perhaps *P. caputmedusa*.</figcaption></figure>
contributions to our knowledge of tintinnids, detailed in
the following sections.

ÉDOUARD CLAPARÈDE (1832–1871) AND
JOHANNES LACHMANN (1832–1860)

The following account is based largely on that
given in Dolan (2021b). When Édouard Claparède ar-
rived in Berlin in 1853 to pursue medical studies, he
met Johannes Lachmann. They were the same age and
quickly became close friends. Lachmann was already
working under Müller and had even gone with him on
a collecting expedition to Trieste. Both Claparède and
Lachmann were, apparently, more attracted to natural
history than either physiology or medicine, and the first
publications of both were on protists, Claparède's study
was on the heliozoan *Actinophyrs eichhornii* (Clapa-
rède 1854) and Lachmann's was on a vorticellid cili-
ate (Lachmann 1856). In the summer of 1856, Müller
invited both to accompany him on a collecting trip. It

was originally planned to go to Messina but the site was
changed to Bergen in Norway due to an outbreak of
cholera in Messina. After about a month, Müller having
failed to find the echinoderm larvae he was seeking, de-
cided to return to Berlin, but encouraged Claparède and
Lachmann to stay on as they were finding interesting
organisms among the 'infinitely small'. They did so,
spending the months of September and October collect-
ing in a variety of sites on west coast of Norway. The
results of the observations and collections formed the
basis of their monographic work "Studies of Infusoria
and Rhizopods" published 1858-1861, part of which
won a prestigious award in Paris (for a detailed account
of the production of their monograph see Dolan 2021b).
They described many new species of protists in their
monograph, including 12, currently recognized as valid
first descriptions of tintinnids in the first part, published
in 1858. This represented a very large increase in the
number of species at the time (see Fig. 2), all them
from their stay in Norway. Unfortunately, they made
mention no mention of the methods they employed.
The plates of Claparède and Lachmann, showing some

<figure><img src="image_7.png" /><figcaption>Fig. 6. Left and center panels, respectively, Plates 8 and 9 with illustrations of tintinnids (and some folliculinides) from the first part of Claparède and Lachmann's monograph published in 1858 (Claparède and Lachmann 1858). The top right and bottom right panels are por- traits of, respectively, Edouard Claparède (ca. 1870) and Johannes Lackmann (ca. 1856).</figcaption></figure>
of the tintinnids they described, is shown in Fig. 6. Sadly, Lackmann died, at the young age of 28, before all 3 parts of their monograph was published. Subsequently, Claparède, did not return to studies of protists but worked on diverse marine invertebrates. He became an ardent defender of Darwin's theory in Switzerland (Hollier and Hollier 2023), as Haeckel did in Germany. Like Lachmann, Claparède died young, at 39 years of age in 1871.

## ERNST HAECKEL (1834–1919)

In 1854, the young Ernst Haeckel arrived in Berlin and joined Claparède and Lachmann as students of Müller, all three ostensibly to study medicine. The three became life-long friends; details are given in Dolan (2021b). Haeckel defended his thesis in March of 1857. It was extravagantly dedicated to Müller: "To the most intelligent teacher these pages are offered by the author with a pious and grateful heart"; Ehrenberg oversaw the thesis defense, and among the three 'opponents' were Claparède and Lachmann (Haeckel 1857). After defending his thesis, Haeckel attempted to practice medicine but quickly abandoned it to pursue studies of natural history. According to Haeckel himself, he had been, early on, encouraged by Müller to study the radiolaria as a subject of great potential when both were visiting Villefranche-sur-Mer in France (see Haeckel

1893; Dolan 2019), and in 1859 Haeckel traveled to Messina to work on radiolaria. The result was one of his first monographs (Haeckel 1862), which along with the monumental Challenger Report (Haeckel 1887) brought Haeckel considerable fame.

Often overlooked among the many accomplishments of Haeckel, is his 1873 "On some new pelagic infusoria" (Haeckel 1873) was a pioneering work as it was the first publication entirely devoted to tintinnids. Interestingly, in it he cites among the previous works concerning tintinnids, a quite discrete mention of his own first observations. It appears as a mere footnote in his 1862 monograph on radiolaria (Haeckel 1862). In the footnote (on page 140), he admits that when he first observed living tintinnids while in Messina, he took them to be radiolarians with a siliceous shell: "Among these siliceous pelagic organisms, I would like to highlight a group of exceptionally delicate, new infusoria with a latticed siliceous shell, which are so similar to several cyrtids, particularly monocyrtids and dicyrtids, that I initially classified them among these families until I later observed the living specimens, which appear to be most closely related to Tintinnus and swim about nimbly by means of long lashes." Haeckel's study of tintinnids can be said to, have begun by the accident of confusing them with radiolarians.

Haeckel's 1873 article is based on his observations of tintinnids made in Messina in 1859–1860 and again in 1866–1867 when he traveled to the Canary Islands as

<figure><img src="image_8.png" /><figcaption>**Fig. 7.** The left panels show the two plates of Haeckel's 1873 publication. The right panels show a portrait of Haeckel (ca. 1868) and "Ciliata," plate 5 of his *Kunstsformen der Natur* (Haeckel 1889–1904) which featured some of his 1873 tintinnid illustrations (the middle of the top half), bringing tintinnids to the general public as artworks of nature.</figcaption></figure>
<figure><img src="image_9.png" /><figcaption>**Fig. 8.** The left panel shows the plate from Fol 1881a, his first article on tintinnids. Depicted are living specimens of forms now known as *Petalotricha ampulla* (center) and *Rhabdonella spiralis*, described for the first time (lower left), and a conjugating pair of *P. ampulla* cells (lower right). The middle panel shows the plate from Fol 1883a, his second article on tintinnids. Depicted are two new species, now known as *Tintinnopsis nucula* (upper left), and *Codonaria cistellula* (middle right), the cellular structures of *P. ampulla* revealed by staining (top right), and the tintinnid associated with a diatom, now known as *Eutintinnus apertus*. The right panel shows the portrait of Hermann Fol ca. 1890, from Bedot (1894).</figcaption></figure>

Barrois. It had government support, and access to ships of the French Navy. Fol then continued work begun in Geneva on the penetration of sunlight into lake water, to study light penetration in seawater using French Navy vessels. Subsequently, in a very unclear series of events (see Dolan 2026), Barrois and Fol were joined by the Russian Alexis Korotneff, forming a larger laboratory, and eventually both Barrois and Fol were evicted from the Villefranche laboratory by Korotneff. Fol then planned to undertake a trans-Mediterranean collecting expedition to study sponges. He purchased and outfitted a steamer in Le Havre, France, departing in September of 1892. The first destination was to be in Nice to collect Fol's sampling equipment. However, Fol, his boat and crew never reached the Mediterranean. No trace was ever found, all are presumed to have been lost at sea.

In Fol's first paper on tintinnids (Fol 1881a) he gave for the first time, detailed description of the oral ciliature, based on observations of living specimens. While he did not observe cell division or the formation of a loricá, he did observe, and describe conjugation, again

for the first time (see Fig. 8). Fol severely criticized Haeckel's characterization of the tintinnid loricá. Fol subjected loricá to various chemical treatments, in an attempt to determine its nature. He found the nature not to be composed of calcium carbonate like foraminifera, nor or be siliceous (as Haeckel had declared) like the skeletons of radiolaria, nor a horny substance, such a turtle shell. Fol suggested that by elimination of these possibilities, the tintinnid loricá maybe chitin- like in nature.

Fol described his 1831 article, based largely on observations of living cells, as a “little work” in his second article (Fol 1883a). The second article was more substantial, giving for the first time, some methods details, for example, on making a net to sample for tintinnids, and methods of preservation as well as preparation of permanent slides with cells suspended in Canada balsam. Using his slides, Fol described the distinct differences in the structural layers of the loricá of different forms known now as *Tintinnopsis*, *Petalotricha*, and *Rhabdonella*. Fol correctly predicted that in the future a large diversity of loricá types would be found. He also
recorded his surprise at finding one form, now known
as *Eutintinnis apertus*, with diatoms attached to its lo-
rica (see Fig. 8). We now know that a variety of tintin-
nids can be found in close associations with diatoms
(Vincent et al. 2018).

GÉZA ENTZ SR. (1842–1919)

The first Géza Entz, now known as Géza Enzt sr.
(senior), was a well-known biologist in his time. Today,
he is perhaps best known as one of the first investiga-
tors of algal symbiosis, especially among protists, along
with Karl Brandt and Patrick Geddes, who, remarkably,
all published papers on the topic at about the same time
(i.e., Brandt 1881; Entz sr. 1881, 1882; Geddes 1882).
Entz did though publish two important works on ma-
rine ciliates, the first on the ciliate fauna of the Bay of
Naples (Entz sr. 1884), largely featuring tintinnids, and
a follow-up article entirely devoted to the lorica of tin-
tinnids (Entz sr. 1885). Before delving into the tintinnid
studies of Géza Entz sr., a brief biography is given.

The following sketch of the life of Géza Entz is
based, except were noted, on the account by Mödlinger

(1976–1977). His father was Ferene Entz, a medical
doctor and naturalist. Géza Entz took a medical degree,
like his father, but by 1867, was a practicing zoologist
as an assistant to a professor of Zoology at Budapest
University. Entz was an avid and early proponent of
Darwin in Hungary, much like Haeckel in Germany,
and Claparède in Switerzland. In 1869, he published the
first account of Darwin's theory in Hungarian (Bonner-
jea 1944). That same year he took his first teaching post
in an agricultural school. In 1873 he was made Profes-
sor of Zoology at Kolozsmonostor University. One of
his assistants was Jenö Daday (Entz and Lukacs 1987),
who would later follow in his footsteps, and investigate
tintinnids in Naples. Entz's future tintinnid expert son,
Géza Entz jr. (junior), was born in 1875. In 1888, Entz
published the first Hungarian textbook on prototzool-
ogy. It was a bilingual book with texts in Hungarian and
German (Entz, sr. 1888). Entz moved to Budapest in
1901 to take the chair of Zoology at Budapest Univer-
sity where he remained until retirement in 1914. Géza
Entz sr. died in 1919 at the age of 77.

Entz's work on tintinnids was conducted in the Zo-
logical Station in Naples. In the introduction of his first
study, he stated that working at Naples station on marine
ciliates was the fulfillment of a long-held desire. The

<figure><img src="image_10.png" /><figcaption>**Fig. 9.** The right panel shows plate 24 from Entz sr. 1884. In the upper left (figs. 1–9) show Entz’s *Codonella beroidea*, now considered to be *Tintinnopsis beroidea*. The large central fig. 17, given the name *Tintinnus Ganymedes* by Entz, after the Greek divinity Ganymede, Zeus’s the cup-bearer. The large conical fig. 13, to the right is Entz’s *Tintinnus Anadyomene*, now known as *Rhabdonella anadyomene*, named after the Greek god Aphrodite. The right panel shows a portrait of Géza Entz sr. at about age 65.</figcaption></figure>
desire was perhaps motivated by his findings that the ciliates of salt lakes were quite diverse (Entz sr. 1879). With regard to tintinnids, he had carefully observed freshwater species, and was convinced that tintinnids were a distinct group of ciliates, different from vorticellids and foliculinids, as previously grouped by some (Entz sr. 1883). His first study, on the ciliates of the Bay of Naples (Entz sr. 1884), was a substantial work of 153 pages of text and 5 plates with illustrations of 39 species. Entz documented the occurrence of 71 species, among which 15 were new species, including four new species of tintinnids (see Fig. 9). Entz sr.'s second study, devoted to tintinnids (Entz sr. 1885), addressed loricara structure in both freshwater and saltwater forms. He named a new freshwater form, based on material found years previously in a pond, brought to him by "Herr Privatdocent Dr. E. Daday," the next 'Pioneer' of tintinnid studies considered here. Tintinnid species named for Entz sr. include *Tintinnopsis entzi* by Daday (1892), *Dicyocysta entzi* by Jørgensen (1924), *Steenstrupiella entzi* and *Undellopsis entzi* by Kofoid and Cambell (1929).

## JENÖ DADAY (1855–1920)

Jenö Daday (who also published as Eugen Daday) was a very productive zoologist. He published nearly 200 works, in Hungarian, German, French and English, with the majority on freshwater crustaceans. He has been heralded as a pioneer of hydrobiology, the world expert in his time on a variety of freshwater metazoans (Forro 1982). However, for tintinnid workers, Daday is known for the first monographic treatment of tintinnids, his 1885 publication. But before considering it and his other publications on tintinnids, it is worthwhile to briefly review his life, revealing his close connection to both the preceding and the succeeding pioneers of tintinnid studies. The following account of Daday's life is based on two memorial publications honoring Daday, the first by the son of Géza Entz sr. (Entz jr. 1925), and the second co-authored by his grandson (Entz and Lukacs 1987).

Jenö Daday was born on May 24th, 1855. The Daday family was of the Hungarian nobility. He was raised in Transylvania, now part of Romania, in his time part of the Kingdom of Hungary. In childhood he had a bent toward natural history. In 1874, after secondary school, he attended the Teacher's College, in the department of Natural History, and pursued studies in mathematics and natural history at the University of Kolozsvár

where Géza Entz was the Professor of Zoology. In 1878, Daday passed his Teacher Examination, but rather than teaching, he became the assistant of Entz sr. In 1883–1884, when Entz sr. went to the Zoological Station in Naples, Daday replaced his mentor, giving private lessons in natural history. When Entz sr. returned, Daday aided his preparation of his article on tintinnid loricaras (as mentioned above), and also caught a desire to study marine ciliates at the Zoological Station in Naples. Granted a government scholarship, Daday worked in Naples from September 1885 to May 1886. On his return, he was first a high school teacher, and in 1887 became an Assistant at the National Museum in Budapest. His personal and professional interactions with Entz sr. were renewed when Entz sr. moved to Budapest in 1889 to take a faculty position at the Technical University. When Entz sr. took his final post as Professor of Zoology at Budapest University, he helped Daday to be named to his former position at the Technical University. In 1902, Daday was named Professor of Zoology in the Technical University. Géza Entz jr. attended his classes and worked for him as his Assistant from about 1910 to 1913. Daday remained at the Technical University until his death of severe bronchitis in 1920, at age 65.

As mentioned above, Daday's stay in Naples to work on 'infusoria' of various types, began just a few months after Entz sr. returned to Budapest. Daday's first publication based on his Naples work (Daday 1886), was similar to Entz sr.'s first publication from his stay in Naples (Entz sr. 1884). It was on a variety of ciliates, and it included some tintinnids (see Fig. 10). Daday modestly titled it "A small contribution to the knowledge of the infusoria fauna of the Gulf of Naples," no doubt in deference to his mentor's work. Recall that Entz sr.'s, second work, based on material collected in Naples was devoted to tintinnids (Entz sr. 1885). Daday's second work (Daday 1887), based on studies in Naples, was also devoted to tintinnids. It was a landmark monograph of 119 pages of text and four large plates. It was the most complete and comprehensive study of tintinnids for many years (Jørgensen 1900; Brandt 1907). In his monograph, Daday characterized 71 species of tintinnids, 26 of which were new. Daday compiled and analyzed all the previous records of tintinnids. He pointed out that most species appeared to be cosmopolitan but noted that nearly all the records were from the waters of Northern Europe with a few from Southern Europe, so drawing conclusions was hazardous. Also from his Naples stay, Daday subsequently published an
<figure><img src="image_11.png" /><figcaption>**Fig. 10.** The left panel is the plate from Daday's first study based on his stay in Naples (Daday 1886) showing a variety of marine ciliates including four species of tintinnids. The center panel is the first of the four plates from Daday's monograph on tintinnids (Daday 1887), showing forms with hyaline loricas. Note presence of the species often found associated with a diatom in the center left, now known as *Eutintinnus apertus*, first portrayed but not named by Fol (see Fig. 8), and given the name *Tintinnus inquilinus* by Daday. The right panel shows a portrait of Daday at about age 40, ca. 1895.</figcaption></figure>

abridged version of his monograph in Hungarian (Daday 1888a), as well as a study of the dinoflagellates of the Bay of Naples (Daday 1888b). Daday's last publication concerning tintinnids appeared a few years later, was a study of “the microscopic fauna of rural lakes” (Daday 1892). In it he described a new tintinnid species, *Tintinnopsis entzi*, named for his mentor.

## GÉZA ENTZ JR. (1875–1948)

Géza Entz jr. had a long life, and as a biologist, he made significant contributions to many fields. Unfortunately for him, the years of his scientific career included severely troubled times, the years of two world wars, and large political upheavals. Likely at least partly in consequence, his contributions to our knowledge of tintinnids appear sporadic, with his important publications appearing in the early 1900's, and subsequently, only a few short publications appeared scattered between 1929 and 1943. However, his early contributions were quite important, and the most important was his 1909 article in the *Archiv für Protistenkunde* (the first journal of Protistology!), but before considering that work, first will be given a brief biography, obviously marked by the influence of both his father, and his father's former student, Daday.

The following account is based on those of Dező (1984) Mödlinger (1976), except where otherwise noted. Géza Entz jr. was born on September 30th, 1875, when his father was 30 years old, and Daday, his father's student and later assistant, was 20 years old. Like Daday, he first pursued higher education in a Teachers College, and Entz jr. received his diploma allowing him to teach in middle schools in 1899. He then studied in Budapest, taking classes at both the Technical University, given by Daday, and classes at Budapest University given by his father. His received his Ph.D. in 1902. He was certified a “Privatdocent” in 1907, allowing him to be paid for tutoring, in the subject of protistology. From 1899 to 1913, Entz jr. worked for Daday, first as an assistant, and then as first assistant. During this period he visited the Naples Station, twice, in 1903 and 1905, both times studying tintinnids (see Entz jr. 1935, 1943). Entz jr. was then the third Hungarian scientist who worked on tintinnids at the Naples Station. In 1913 he took a job as a biology teacher at a teacher's college that he retained until 1920 when he chose to exile himself as political machinations denied him the chair of Zoology at the Budapest University. Entz jr. accepted a post as ‘first assistant’ at the Zoological Institute of Utrech University in Holland, and then worked his way up to Associate Professor. During summer vacations, he worked at a marine station, and continued his
<figure><img src="image_12.png" /><figcaption>**Fig. 11.** The left and center panels show the fourth and fifth plates in both Entz jr. 1908 and 1909. The right panel shows an undated portrait of Géza Entz jr., perhaps at about age 60 in 1935.</figcaption></figure>

observations of tintinnids (see Entz jr. 1929, 1943). He returned to Hungary in 1929, was made Director of the Hungarian National History Museum in 1932, and in 1934 was named Professor of Zoology at Budapest University, the chair previously occupied by his Father. Géza Entz jr. passed away on February 21, 1943, having suffered “a long and grave disease.”

Entz jr. published substantial works on tintinnids. The first appeared in 1904, a study of the tintinnids of the coast of the Northern Adriatic in Croatia, based on samples he collected, and some supplied by Daday (Entz jr. 1904). The second was a review of freshwater tintinnids (Entz jr. 1905). His third and major publication appeared first in Hungarian, the very rarely cited “A Tintinnidak szervezete” (The organisation of the Tintinnidae), a large monograph of 134 pages of text and 13 plates (Enzt jr. 1908). A much better known German language version was published in the *Archiv für Protistenkunde* as “Studies on the organization and biology of tintinnids” (Entz jr. 1909). The study concerned not only the taxonomy of tintinnids with a review, and many striking illustrations, of the species he encountered while in Naples (see Fig. 11), but also extensive data on the cytology of tintinnids, based on the examination of thin sections of cells, and the cytology

of conjugation. His study concluded with a quite comprehensive bibliography listing 171 studies focused on, or simply touching on, tintinnid ciliates. His reference covered the period from the first description of a tintinnid, correctly citing the 1776 *Prodomus*, to the works of Brandt, quite recent at the time, which will be explored in the next section.

## KARL BRANDT (1854–1931)

Karl Brandt produced a landmark monograph on tintinnids from his participation in Victor Hensen's Plankton Expedition (see Dolan 2021a), but he is actually best known today as a major figure in the development of oceanography and plankton studies (Mills 1989). Before presenting the tintinnid works of Brandt, a short biography is provided based on Reibisch (1931) showing that his works on tintinnids have a rather mysterious origins.

Karl Brandt was born on May 24th 1854, in Magdeburg. In his higher education, and first works, parallels are apparent with both Claparède and the Hungarianioneers. Brandt studied ‘natural sciences’ in Berlin under Gustav Fitsch who occupied the Chair of Physiology,
once that of Johannes Müller, under whom Claparède studied, at the Berlin University. In 1877, Brandt was granted his doctorate with his dissertation on a heliozoan, *Actinosphaerium eichhorni*, the subject of Claparède's first publication. The subject of Brandt's first publication was also on heliozoa (Brandt 1878), but neither Claparède nor Brandt published further on heliozoa, both turned towards marine protists. Brandt's decisive turn toward marine protists coincided with his work at the Naples Zoological Station beginning in 1879, where Entz sr., Daday, and Entz jr. later conducted their tintinnid studies. Brandt, however, began his studies of protists of the marine plankton with investigations concerning radiolaria, and as mentioned above, he was first concerned with the algal symbionts of radiolaria (Brandt 1881, 1883). He actually worked as an assistant at the Naples Station from 1882–1885. He likely knew Entz sr. and Daday at the time. When he returned to Germany, Brandt went to Königsberg where he passed qualification examinations to be a lecturer in Zoology in 1885, and by 1889, was named Professor of Zoology at Kiel University where he remained until his retirement in 1922 at age 68. He passed away in early 1931.

Brandt's work on tintinnids began long after his studies of radiolaria that culminated in his 1885 monograph on colonial radiolaria (Brandt 1885). His first

tintinnid work did not appear until 1896. It was among a set of papers, each concerning a distinct taxonomic group such as ctenophores, appendicularia and annelides, reporting on samples gathered in voyages between Greenland and Copenhagen in 1892–1893. In his report on the tintinnids found in the samples (Brandt 1896), he did not mention why he undertook the study of tintinnids, organisms not mentioned in any of his previous publications, except as possible prey items of radiolaria. He merely stated that Vanhöffen, who himself reported on the ctenophores (Vanhöffen 1895), had done a preliminary analysis of the samples and provided his notes. Perhaps Brandt had seen tintinnids when sampling for radiolaria during his years in the Zoological Station in Naples, as Haeckel had in Messina, and Brandt knew the works of Entz sr. and Daday published in the reports of the Zoological Station? Regardless, Brandt's report was the first work on Arctic tintinnids, and he described 15 new species (see Fig. 12). Several years passed before Brandt's most important, his second and last, contribution to tintinnid studies. It was his massive monograph based on samples gathered during Victor Hensen's “Plankton-Expedition” in 1889, as the zoologist aboard the *National*. Brandt's treatment of the tintinnids from the samples collected, and previous sampling (i.e., Brandt 1896), consisted of a total of

<figure><img src="image_13.png" /><figcaption>**Fig. 12.** The left panel shows the plate from Brandt 1896, his first publications on tintinnids in which he described new species of boreal and arctic tintinnids. The center panel shows plate 46, illustrating species now known as *Xystonellopsis dicymatica* and *X. pulchra*, from his 1906–1907 Plankton-Expedition monographs. The right panel shows an undated portrait of Karl Brandt from Reibisch 1931.</figcaption></figure>
521 pages of text and 70 plates (Brandt 1906, 1907), making it one of the largest work on tintinnids to have ever appeared before, or since. Again, rather mysteriously, it appears to be the only purely systematic work among Brandt's many publications on a wide variety of topics (Reibisch 1931). In the Plankton-Expedition monograph, Brandt described 34 new species (some shown in Fig. 12), many with multiple varieties that were later raised to species status by Kofoid and Campbell. Consequently, today Brandt is credited, in total, as having provided the original description of 79 currently accepted species of tintinnids.

## EUGEN JØRGENSEN (1862–1938)

Eugen Jørgensen (also spelled Jörgensen) published extensively on various protist taxa of the marine plankton, and produced two important works focused on tintinnids. However, before the works on tintinnids are considered, it is worth briefly reviewing Jørgensen's career as it shows how he became an expert on protist taxa of the marine plankton through accidents of circumstances. The account given here of his career is based on that given in Dolan (2024c) and references therein.

Jørgensen trained to become a high school teacher and was a high school teacher for his entire working life. However, his first passion, occupying his vacations, was botany, especially Arctic flora. After working

in several high schools in remote localities of Northern Norway, in 1895 he was hired to teach in the Cathedral High School in Bergen. By that time he had published a substantial work on Arctic flora and was so granted an office and some working space in the Botany department of the prestigious Bergen Natural History Museum. The accidents of circumstance leading Jørgensen, the Arctic plant expert, to work on protists of the plankton were first, the establishment of the Museum's marine station on the Puddefjord, in the city of Bergen in 1892 just a few years before Jørgensen's arrival in Bergen. It was located only 1.5 km from the Natural History Museum. Second was the naming of Ole Nordgaard as the first director of the new station. He was a zoologist, the same age as Jørgensen. He also was a high school teacher who worked in the Museum of Natural history. When Nordgaard began working on cataloging the organisms of the Puddefjord plankton in 1898, he turned to the new botanist of the Museum for aid in investigating the microplankton in his plankton net samples, dominated by diatoms and dinoflagellates, groups considered at the time to be in the domain of botany. Soon, Jørgensen was collecting his own samples, became friends with Norgaard, and they worked together for several years until Norgaard left Bergen in 1905 for a post in Tromsø. While Jørgensen never abandoned classic botany, most of his publications were on protist taxa of the marine plankton.

<figure><img src="image_14.png" /><figcaption>**Fig. 13.** The left panel shows the first of 3 plates in Jørgensen 1900. The middle panel shows figures 11–25 from his 1924 monograph on Mediterranean tintinnids. In the lower right are three forms he described as new species of *Amphorella*. They are now known *Cantheriella pyrimidata* (17), *Steenstrupiella intumescens* (18), and *Ormosella trachelium* (21). The right panel is a portrait of Jørgensen at about age 38 (ca. 1900).</figcaption></figure>
Jørgensen's first work dedicated to tintinnids was his study of the tintinnids of the West Coast of Norway (Jørgensen 1900). Recall that the first substantial additions to the number of known species of tintinnids was from the work of Claparède and Lackmann during their stay in the region of Bergen in 1856. Jørgensen pointed out that since 1856, the tintinnids had not been studied. His work was based on observations made at the Bergen Marine Station, including many observations of live organisms. He found many forms absent from Claparède and Lachmann's study, he described three new species (see Fig. 13), and several new varieties of species, some later raised to species status by Kofoid and Campbell (1929).

Jørgensen's second work, and most important work devoted to tintinnids, appeared many years later. It was the last of his three reports on samples collected during "Danish Oceanographical Expeditions 1908-10 to the Mediterranean and Adjacent Seas." True to form as botanist, the first two reports "Mediterranean Ceratia" (Jørgensen 1920) and "Mediterranean Dinophysiaceae" (Jørgensen 1923), concerned phytoplankton. It was the third, his "Mediterranean Tintinnidae" (Jørgensen 1924) that is his lasting contribution to tintinnid studies. It was the first synoptic study of an entire sea based on samples taken across the Mediterranean Sea in both summer and winter. Jørgensen's was a quite substantial study of 110 pages of text illustrated with 114 figures. He documented the occurrence of 92 species, representing 23 genera, and described 21 new species many of which were transferred to other genera by Kofoid and Campbell (e.g., see Fig. 13). It was one of Jørgensen's last publications on protists. He passed away in 1938 at the age of 74.

## CHARLES KOFOID (1865–1947) AND ARTHUR CAMPBELL (1899–1972)

The appearance of two major monographs by Kofoid and Campbell, the first in 1929, and the second in 1939, mark the end of the 'pioneers of tintinnid studies'. The two monographs are quite different in many ways, nearly as distinct from one another as the two authors, Kofoid and Campbell, were from one another. Here, first brief sketches of the lives and careers of the two men will be given before a close look at their two major works on tintinnids.

The following account of Kofoid is based on a memorial article by Goldschmidt (1951) and the others cited within. For details on aspects of his career see Dolan (2022b). Kofoid was raised on a farm in Illinois (USA). He first attended Oberlin College, then did graduate work at Harvard, gaining a Ph. D. in biology in 1894. At Harvard, Kofoid became friends with William E. Ritter, a connection of importance in later years. Kofoid joined the University of Illinois as Assistant Professor in 1895 and was named Superintendent of the Illinois Biological Station where he began his work on the organisms of the plankton, focusing first on Lake Michigan (Kofoid 1896). Kofoid's studies of the Illinois River culminated with two massive tomes on the plankton of the Illinois River, totaling almost 1000 pages (Kofoid 1903, 1905a). Meanwhile, his friend Ritter in California had risen to the rank of Chairman of the Department of Zoology at the University of California. In his new position, Ritter sought to add faculty who did field work, especially those who could be enticed to participate in the creation of a marine laboratory, one of his fervent hopes. Ritter asked his old friend Kofoid to join the faculty at the entry-level position of Assistant Professor, which Kofoid did in 1903, remaining at the University until his retirement in 1936.

Kofoid rose quickly through the academic ranks. He was made an Associate Professor in 1904, and in 1910 was made a Professor and Chairman of the Department of Zoology. Kofoid was quite active in the creation and administration of Ritter's marine laboratory, serving as Assistant Director of the station in San Diego in 1907–1910, and again when the laboratory found its permanent home in La Jolla, from 1910–1923, where it became the Scripps Institute of Oceanography in 1923. It appears likely that working in waters in Southern California is where Kofoid first encountered dinoflagellates and tintinnids of the marine plankton, which became the major subjects of his publications from 1905 to 1912, especially the dinoflagellates.

Of great importance in the story of the tintinnid monographs of Kofoid and Campbell is Kofoid's participation in Alexander Agassiz's last major voyage of exploration to the South Pacific in 1904–1905. Kofoid was charged by Agassiz with the study of the microplankton, specifically diatoms, radiolaria, and tintinnids (Agassiz 1905). It is curious that Agassiz recruited Kofoid to work on marine microplankton because he had not yet published on marine protists, and actually never did publish on the diatoms or radiolaria. However, Kofoid's collections made during the six months cruise of
the Albatross formed the basis of his studies of dinoflagellates and tintinnids, including the two monographs on tintinnid ciliates, treated below following a sketch of the life of Kofoid's co-author, Arthur Campbell.

The sketch presented here of his career is based on that pieced together previously (Dolan 2021c) from diverse sources as no memorial notices were published on Campbell, in contrast to numerous articles on Kofoid. Campbell was born in 1899, the only child of a couple living in San Bernardino (CA, USA). He attended Pomona College in Southern California and worked at the Laguna Marine Laboratory of Pomona College, in Laguna Beach California. Campbell published several papers in the journal of the college on various marine invertebrates. After graduating in 1921, Campbell was briefly a faculty member of the Canton Christian College in southern China. He returned to the United States in 1923, when granted a fellowship to pursue a Masters Degree at Harvard College, and he was awarded his degree (topic unknown) in 1924. In 1925, Campbell was a Ph.D. Candidate and Teaching Assistant in the Department of Zoology at the University of California, and was granted his Ph.D. in 1926 (or 1927) with his thesis "The cytology of Tintinnopsis nucula (Fol.) Laachmann with an account of its neuromotor system, division, and a description of a new intra-nuclear parasite." In the published version (Campbell 1926a), he acknowledged Kofoid's role in his studies, "The writer takes this occasion to express his indebtedness to C.A. Kofoid, at whose instance the investigation was undertaken, for kindly and suggestive aid." It is tempting to attribute Kofoid's 'instance' to the account of a neuromotor system in the tintinnid. Kofoid's "neuromotorium" was an alleged protist organelle, a veritable 'nervous system', described by primarily by a very long series of his graduate students (from 1914 to 1937) in protistan taxa of ciliates, flagellates, and rhizopods. The "neuromotorium," Kofoid's spectacular mistake, was eventually shown to be an artifact of fixation protocols and staining (see Dolan 2022b for details). As a new Ph.D., Campbell's first academic position was in his hometown at San Bernardino Valley Union Junior College. However, by late 1928, he was giving his official affiliation as Saint Mary's College (Moraga, CA), about 20 km from the University of California campus in Berkley. He had held a part-time position at the college during his studies. It was a small, Catholic liberal arts college. Campbell taught Zoology at Saint Mary's, and remained there until his retirement in 1961.

Kofoid and Campbell's 1929 monograph with the long official title *A Conspectus of the Marine and Freshwater Ciliata belonging to the Suborder Tintinnoidinea, with Descriptions of new Species Principally from the Agassiz Expedition to the Eastern Tropical Pacific 1904-1905* (from here on *Conspectus*) appeared on December 31st, 1929. Its nature is easily defined. It is a compendium and re-organization of all tintinnid species and forms known at the time, and included the integration of new species found in the samples during the Expedition of the Albatross in 1904-1905. As a synoptic review, it constitutes the keystone work in the study of tintinnids. However, there are oddities concerning the monograph that have not been previously noted.

In the introduction, the *Conspectus* is presented as a needed precursor to a work in progress focused on the tintinnids found in the collections of the Albatross Expedition, the one eventually published some 10 years later. Why was a work in progress on the tintinnids of the Albatross Expedition if all the new species found in the collections are described in the *Conspectus*? Next, the genesis and production of the monograph are obscure. The synoptic review was said to be needed to precede a work on the tintinnids of the Expedition collections due to the plethora of names and forms existing in the literature on tintinnids. However, the exact same situation applied with regard to dinoflagellates, but did not prevent Kofoid from publishing on them. He contributed several reports to the series on the Albatross Expedition on new species and forms of dinoflagellates and the reports began appearing early on, and after, the appearance of the *Conspectus* (i.e. Kofoid 1907, 1909; Kofoid and Michener 1911; Kofoid and Rigden 1912; Kofoid and Skogsberg 1928; Kofoid and Adamson 1933). How the *Conspectus* was produced, specifically who did what work, is not mentioned in the Introduction. While a lack of some sort of statement of "author contributions" was common at the time, with regard to the *Conspectus*, the absence contrasts with Kofoid's detailed statements in the previous report on new tintinnids from San Diego (Kofoid 1905b), the 1939 tintinnid monograph (Kofoid and Campbell 1939), and the earlier monographs on dinoflagellates (Kofoid and Swezy 1921; Kofoid and Skogsberg 1928).

As mentioned previously (Dolan 2021c), there are reasons to suspect that the *Conspectus* was largely the work of Campbell. Here, some details are provided. Kofoid had previously published only three papers on tintinnids, totaling 30 pages, with the most recent dating from 1915 (Kofoid 1905, 1912, 1915). From the
‘Acknowledgements’ of the 1939 tintinnid monograph, Kofoid supervised the work of his assistant, Elizabeth Heald Purington, who examined the samples of Albatross Expedition, noted species occurrence, and made illustrations, from 1910 to 1917. Thus, it appears that Kofoid had apparently not worked on tintinnids himself for at least a decade when Campbell began his studies of tintinnids in 1925. Furthermore, Kofoid’s research shifted to a focus on symbiotic and parasitic protists by 1915. Campbell, on the other hand, by 1929 had published four works on tintinnids, totaling 85 pages, the most recent dating from 1929 (Campbell 1926a, b, 1927, 1929). The last oddity with regard to the *Conspectus* is that although it presented over 200 new species from the Albatross Expedition, it was not published with the other reports in the series of Expedition Reports in the *Bulletin of the Museum of Comparative Zoology at Harvard*. It was published in the serial the *University of California Publications in Zoology*, edited by Kofoid.

In the *Conspectus*, 697 forms of tintinnids are catalogued, given species status, and figured. These were 493 forms in the existing literature of the time, many previously described only as forms or varieties of a species, now given species status, and 204 forms found in the samples from the Albatross Expedition described as new species or given new names. Figures were provided for each species, the overwhelming majority of only the lorica (of the 697 figures only four depicted a ciliate in the lorica). The artwork was not credited although many figures were apparently original. All of the figures were appeared at the low magnification of 200×, compared to the figures of Brandt or Jørgensen, printed at 300–500× in large format publications. Consequently, in print, many figures in the *Conspectus* are quite small, considerably smaller than the original figures. For example, their Fig. 15 of *Tintinnopsis nana* “after Lohmann 1908,” is 0.25 cm tall (see Fig. 14 below), while the original figure was printed 1.25 cm tall (Lohmann 1908). In addition, lengths were given only

<figure><img src="image_15.png" /></figure>

**Fig. 14.** The left panel shows the first set of the figures of *Tintinnopsis* species on page 22 of the *Conspectus*. The printed sizes of many figures was quite small, with the most diminutive being T. nana, in the upper right. All of the figures were 200× magnification. The middle panel shows plate 28 of Kofoid and Campbell’s 1939 monograph depicting *Canthariella*, *Steenstrupiella*, *Amphorella*, *Amphorellopsis*, *Ondontophorella*, and *Daturella*. The figures in the 1939 plates were almost all shown at 336× magnification. The top right panel is a portrait of Kofoid in 1935, aged 70, shortly before his retirement. The bottom right panel is a portrait of Campbell, ca. 1929, at age 30.
for species newly described or re-named. Thus, adding a size bar to each set of the figures in the *Conspectus* would have made it actually ‘user-friendly’, and thereby greatly increased its value to the community.

The appearance of the *Conspectus* was noted only in passing in the *Quarterly Review of Biology*, as a book received (Anon. 1930). Perhaps luckily for Kofoid and Campbell, the only full review, scathingly negative, was in a German language journal, *Naturwissenschaften*. The review took issue with the singular reliance on the lorica in characterizing species, the complete absence of consideration of characteristics of the ciliate itself, and the proliferation of new species, likely to be only morphological variants of known species (Hofker 1930).

In April of 1939, a few months short of ten years after the *Conspectus* appeared, the official report on the tintinnids found in the samples collected during the Albatross Expedition was published in the *Bulletin of the Museum of Comparative Zoology at Harvard College*. The second monograph (Kofoid and Campbell 1939) is quite comparable in size and contents to its predecessor, with 473 pages of text and 496 figures. However, the organization is completely different with the figures in plates at the end of the volume. Most of the artwork in the 35 plates of illustrations of tintinnids was credited to Elizabeth Heald Purington, Kofoid’s former Master’s student (Heald 1911) and assistant from 1910 to 1917. It is a revision of tintinnid genera and species of the *Conspectus*. They added 9 new genera to the previous 52 genera and added 25 new species. Oddly, the introduction omits any mentions of the how, why, and when the needed changes to the *Conspectus* came to light. During the interval between the *Conspectus* and the 1939 monograph, Campbell produced his monograph on the tintinnids from the collections of the last voyage of the Carnegie (Campbell 1942). Although published in 1942, it was submitted in 1937. One might speculate that working on the Carnegie samples coincided with finding some revision needed to the *Conspectus*.

## “INQUIRENDA ET CORRIGENDA”

Discerning readers will likely notice that some notable personalities among early workers, i.e. who made substantial contributions to tintinnid studies, are absent from the preceding narrative. This was for various reasons, ranging from a need to limit the length of the present review, to a lack of information

on them. Here are simply mentioned the most notable omissions, along with their important contributions. A.W. Schweyer published an early work on lorica formation (Schweyer 1909). Hans Laackmann produced the first, (Laackmann 1907), and the enduring major work on tintinnids in Antarctica (Laackmann 1910). Alphonse Meunier produced two works in which a number of new tintinnids species were described, one on arctic protists (Meunier 1910), the other on protists of coastal waters of Belgium (Meunier 1919). J. Hofker, whose first name remains unknown!, published an important article on the cytology and cell division of tintinnids (Hofker 1931).

## CONCLUSION

The early protistologists who worked on tintinnids (and other groups of protists) came from a variety of backgrounds. Some held medical degrees, such as É. Claparède, J. Lackmann, E. Haeckel, H. Fol, and G. Entz sr., and later worked as university or college faculty. Remarkably though, many were actually primarily teachers, beginning with O. F. Müller, a tutor, followed by J. Daday, G. Entz jr. and E. Jørgensen whose with their first diplomas allowed them to teach in middle schools or high schools, and the university teachers, K. Brandt, C. Kofoid and A. Campbell. Only one, H. Fol, was wealthy and had no need to work for a living. Much like protistologists today, the early workers were not employed to study a specific group of protists, but did so because their employment allowed them to study protists. In the early days, and much like today, Protistology is not so much a career as it is a passion.

**Acknowledgements.** The author is sincerely thankful for the willingness of the reviewers to evaluate this lengthy work and their useful and thoughtful comments. Nonetheless, I retain full responsibility for all errors of fact, omission, and interpretation.

**Supplemental File.** The supplemental Excel file, ‘PioneerSuppFileTinPubs.xlsx’ contains the full references to the 151 publications which have appeared in the past ten years (2016–2025) with the term tintinnid, or a variant, in the title.

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Received on 1st January, 2026; revised on 10th January, 2026; accepted on 12th January, 2026