Uniciencia Vol. 35(1), pp. 210-230, January-June, 2021
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DOI: http://dx.doi.org/10.15359/ru.35-1.13
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Onychophorology, the study of velvet
worms, historical trends, landmarks, andresearchers from 1826 to 2020(a literature review)
Onicoforología, el estudio de los gusanos de terciopelo, tendencias históricas,
hitos e investigadores de 1826 a 2020 (Revisión de la Literatura)
Onicoforologia, o estudo dos vermes aveludados, tendências históricas,
marcos e pesquisadores de 1826 a 2020 (Revisão da Literatura)
Julián Monge-Nájera1
Received: Mar/25/2020 • Accepted: May/18/2020 • Published: Jan/31/2021

Abstract
Velvet worms, also known as peripatus or onychophorans, are a phylum of evolutionary importance thathas survived all mass extinctions since the Cambrian period. They capture prey with an adhesive net thatis formed in a fraction of a second. The first naturalist to formally describe them was Lansdown Guilding(1797-1831), a British priest from the Caribbean island of Saint Vincent. His life is as little known as thehistory of the field he initiated, Onychophorology. This is the first general history of Onychophorology, which
has been divided into half-century periods. The beginning, 1826-1879, was characterized by studies fromformer students of famous naturalists like Cuvier and von Baer. This generation included Milne-Edwards
and Blanchard, and studies were done mostly in France, Britain, and Germany. In the 1880-1929 period,
research was concentrated on anatomy, behavior, biogeography, and ecology; and it is in this period when
Bouvier published his mammoth monograph. The next half-century, 1930-1979, was important for the
discovery of Cambrian species; Vachon’s explanation of how ancient distribution defined the existenceof two families; DNA and electron microscopy from Brazil; and primitive attempts at systematics using
embryology or isolated anatomical characteristics. Finally, the 1980-2020 period, with research centeredin Australia, Brazil, Costa Rica, and Germany, is marked by an evolutionary approach: from body andbehavior to geographic distribution; the discovery of how they form their adhesive net; the reconstructionof Cambrian onychophoran communities, the first experimental taphonomy; the first country-wide mapof conservation status (in Costa Rica); the first model of why they survive in cities; the discovery of new
phenomena like food hiding, parental feeding investment, and ontogenetic diet shift; and the birth of a
new research branch, onychophoran ethnobiology. While a few names often appear in the literature, mostknowledge was produced by a mass of researchers who entered the field only briefly.
Keywords: history of science, the study of invertebrates, research patterns, studies on onychophorans.
Julián Monge-Nájera,
jmonge@uned.ac.cr, https://orcid.org/0000-0001-7764-2966
1 Laboratorio de Ecología Urbana, Universidad Estatal a Distancia, San José. Costa Rica

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Resumen

Os vermes aveludados ou onicóforos, são um filo de importância evolutiva que sobreviveu a todas as
extinções massivas desde o período cambriano. Capturam suas presas com uma rede adesiva que seforma em uma fração de segundo. O primeiro naturalista que os descreveu foi Lansdown Guilding (17971831), um sacerdote britânico da ilha caribenha de San Vicente. Até o momento, nenhuma história sobreo estudo destes animais tinha sido escrita: este artigo é a primeira História Geral da Onicoforologia. Os
primeiros estudos, de 1826 a 1879, foram publicados por estudantes de naturalistas famosos como Cuvier
e von Baer. Dentre esses estudantes estavam Milne-Edwards e Blanchard, e os estudos foram feitos, em
sua maioria, na França, Alemanha e Grã-Bretanha. No período de 1880-1929, o trabalho se concentrou
na anatomia, comportamento, biogeografia e ecologia, e apareceu a grande monografia de Bouvier. O
período seguinte, 1930-1979, foi importante pelo descobrimento de fósseis cambrianos; a explicação de
Vachon sobre como a distribuição antiga definiu a existência de duas famílias; estudos no Brasil com DNAe microscopia eletrônica; e tentativas primitivas de sistemática utilizando embriologia ou características
anatómicas isoladas. Finalmente, o período de 1980-2020, com pesquisas focadas na Austrália, no Brasil,na Costa Rica e Alemanha, está marcado por um enfoque evolutivo de todos os campos, desde o corpo e ocomportamento, até que a distribuição geográfica; o descobrimento sobre como formam sua rede adesiva;

Julián Monge-Nájera

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Resumowww.revistas.una.ac.cr/uniciencia •Palabras clave: historia de la ciencia, estudio de invertebrados, patrones de investigación, estudio de onicóforos.

UNICIENCIA Vol. 35, N°. 1, pp. 210-230. January-June, 2021 •Los gusanos de terciopelo, peripatos u onicóforos, son un filo de importancia evolutiva que ha sobrevivido
a todas las extinciones masivas desde el Cámbrico. Capturan sus presas con una red adhesiva que se forma
en una fracción de segundo. El primer naturalista que los describió fue Lansdown Guilding (1797-1831),
un sacerdote británico de la isla caribeña de San Vicente Su vida es tan poco conocida como el campo
científico que él inició, la onicoforología. Este artículo es la primera historia general de la Onicoforología,
aquí dividida en periodos de 50 años. Los primeros estudios, de 1826 a 1879, fueron publicados por
estudiantes de naturalistas famosos como Cuvier y von Baer. Entre estos estudiantes estaban MilneEdwards y Blanchard, y los estudios se hicieron mayormente en Francia, Gran Bretaña y Alemania. En elperíodo 1880-1929, el trabajo se concentró en anatomía, comportamiento, biogeografía y ecología, y es
en este período cuando apareció la gran monografía de Bouvier. El siguiente periodo, 1930-1979, fue
importante por el descubrimiento de fósiles cámbricos; la explicación de Vachon de cómo la distribución
antigua definió la existencia de dos familias; estudios en Brasil con ADN y microscopía electrónica; e intentos
primitivos de sistemática utilizando embriología o características anatómicas aisladas. Finalmente, el
período 1980-2020, con investigaciones centradas en Australia, Brasil, Costa Rica y Alemania, está marcado
por un enfoque evolutivo de todos los campos, desde el cuerpo y el comportamiento, hasta la distribución
geográfica; el descubrimiento de cómo forman su red adhesiva; la reconstrucción de las comunidades delCámbrico, la primera tafonomía experimental; el primer mapa del estado de conservación en todo un país(de Costa Rica); el primer modelo de porqué sobreviven en las ciudades; el descubrimiento de nuevos
fenómenos, como ocultar alimentos, inversión en alimentación parental y el cambio ontogenético de dieta;
así como el nacimiento de una nueva rama de investigación, la etnobiología de onicóforos. Si bien algunos
nombres aparecen a menudo en la literatura, la mayoría del conocimiento fue producido por una masa deinvestigadores que ingresaron al campo brevemente.

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Palavras-chave: história da ciência, estudo de invertebrados, padrões de pesquisa, estudo de onicóforos.

INTRODUCTION

Other people probably saw onychophorans before Guilding (Costa Rican farmers refer to them as “slugs withlegs”), but he was the first to describe
them in a scientific paper (Guilding,1826). It is hard to imagine the world inwhich he lived, where slavery was legal, Beethoven was still alive and no one
knew that bacteria existed and caused disease. The Reverend Lansdown Guilding(1797-1831) was a British naturalist fromthe Caribbean island of Saint Vincent. He
was mainly a botanist, a brilliant young212

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Julián Monge-Nájera

A new phylum is discovered among
humble plants: 1826 to 1879

www.revistas.una.ac.cr/uniciencia •Velvet worms, or onychophorans,
include placental species and, as a phylum, have survived all mass extinctions
since the Cambrian (Hutchinson, 1930;
Hou, & Bergström, 1991). They capture
prey with an adhesive net that is formed inless than a second (Dendy, 1889; Concha
et al., 2015). There is not a single general history of this branch of science called
onychophorology; the word does not evenappear in dictionaries at the time I write
this (May 2020, the year of the COVID
19 pandemic), but it has been used for
decades by the Centre International de
Myriapodologie in Paris (https://myriapodology.org/). A definition is in order, so
here is mine: Onychophorology is a fieldof biology that studies the phylum Onychophora and all subjects related toonychophorans in all fields of research.
These animals are important in the studyof evolution, but only interest a minusculefraction of the scientific community. If all
the onychophorologists active in the year
2020 were inside a bus, there would bemany empty seats.
Here I summarize the historical
trends, landmarks and researchers who
have defined the history of Onychophorology for almost two centuries. This analysis of the literature is based on reading
and selecting, based on my experience ofmany years in the field; from my personal
perspective, I have chosen articles basedon three criteria: being the first on a particular subject (e.g. Peters, 1880, the first
to focus on leg variation); being comprehensive (the large monograph by Bouvier, still used today: Bouvier, 1905, 1907);
or marking a decade (e.g. the article byHill, 1950, which was followed by several other popularization articles aroundthe world in that decade). The comprehensive bibliography that I used to selectthe papers listed here is the General Bibliography of Onychophora, available online under a Creative Commons license:
https://zenodo.org/record/3698134#.
XmEuBBP0nOQ

UNICIENCIA Vol. 35, N°. 1, pp. 210-230. January-June, 2021 •a reconstrução das comunidades do Cambriano, a primeira tafonomia experimental; o primeiro mapa do
estado de conservação em todo um país (da Costa Rica); o primeiro modelo do porquê sobrevivem nas
cidades; o descobrimento de novos fenômenos, como ocultar alimentos, investimento em alimentação
parental e a alteração ontogenética de dieta; como também o nascimento de um novo ramo de pesquisa,
a etnobiologia de onicóforos. Embora alguns nomes apareçam com frequência na literatura, a maior parte
do conhecimento foi produzida por uma massa de pesquisadores que entraram brevemente em campo.

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www.revistas.una.ac.cr/uniciencia •Fig 1. A giant onychophoran from
Costa Rica, and six pioneers of
Onychophorology.

Source: Alejandro Solórzano (worm) and, for the
portraits, https://commons.wikimedia.org/

Eduard Grube (1812-1880), then a lecturer inzoology in Dorpat, Germany. Grube, a student of the famous von Baer, father of embryology, was himself a recognized authority
on invertebrates and specialized in Mediterranean polychaete worms (Grube, 1853).
The 1860s were poor in production,
characterized by short notes, but for the firsttime in Europe (because it had been done
earlier in Chile) we see the inclusion of the
new animals in a general zoology, in thiscase, the Leipzig Handbuch der Zoologie(Carus, 1863).

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Julián Monge-NájeraUNICIENCIA Vol. 35, N°. 1, pp. 210-230. January-June, 2021 •man who corresponded with Darwin andHooker; Hooker described him as “an arrogant, demanding, ambitious, and often
conceited individual, all too ready to ask
for unusual favors” (Howard & Howard,1985). We know little else about Guilding,other than his first wife died “in childbed”
leaving five children behind and that hedied of unknown causes in 1831 whileon vacation in another island (Howard &Howard, 1985).
Of the first and only onychophoran
he ever saw, he wrote “it inhabits primary forests in Saint Vincent, often walks
backward. If pressed, it releases viscous
liquid from the mouth. Among the plantsthat I collected at the foot of mount ‘Bon
Homme´, I, astonished, discovered bychance the only specimen” (Monge-Nájera, 2019).
Seven years after the publication,and two after Guilding’s death, two Frenchzoologists, Jean Victor Victoire Audouin(1797-1841) and Henri Milne-Edwards(1800-1885; a student of Georges Cuvier) moved onychophorans from mollusks
to annelids (Audouin & Milne-Edwards,
1833). Soon afterwards, the scientificworld received the news that the animal
was also found half a world away, in South
Africa (Gervais, 1836). Some pioneers in
the field appear in Figure 1.
During the 1840s the animals werestudied by classical French luminaries Jeande Quatrefages and Émile Blanchard (Quatrefages, 1848; Blanchard, 1847). Blanchard
also wrote the onychophoran chapter for themonumental book series Historia Físicay Política de Chile edited by Claude Gay(1800-1873) a French naturalist who did
natural history in Chile (Blanchard, 1849).
The raising of onychophorans to theirown phylum was done in 1853 by Adolf

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They are all over the world! Bouvier enters the scene: 1880 to 1929

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Julián Monge-Nájera

www.revistas.una.ac.cr/uniciencia •The already notable growth in publications from the previous decade was followed by an even more spectacular increasein the 1880s, with papers on anatomy, embryology, ecology, geographic distribution
and behavior. It was also the time of theoldest thesis on these animals that I could
find: a study on the anatomy and histology
of “peripatus” from the University of Breslau, in what is now Wrocław, Poland (Gaffron, 1883).
The embryology papers were about
species from South America (Sclater, 1888),
South Africa (Balfour, 1883; Sedgwick,1884) and New Zealand (Sheldon, 1887).
Others dealt with compared anatomy of thebrain (Saint-Remy, 1889) and the pharynx(Nicolas, 1889), the origin of metamerism(Sedgwick, 1884), and the first study focused on how the number of legs varies, thisone from South Africa (Peters, 1880).
Ecological papers described the habitat of species from New South Wales (Bell,1887) and New Zealand (Kirk, 1883), andReverend Adam Sedgwick, Darwin’s geology teacher, published the first monographof species and their geographic distribution(Sedgwick, 1908a). Smaller papers expanded the known distribution of the phylum inAsia and Oceania (e.g. Horst, 1886).
The Onychophora report from the
H.M.S.Challenger was also published inthis decade (Anonymous, 1885) as well as
the first study about the animal’s movements (Haase, 1889).
The decade of 1890 was marked bymany natural history notes, as more specimens were found around the globe; there
was less embryology and more ecology.
A study compared ovum development
in South Africa and New Zealand (Sheldon, 1890) and Prenant (1890) described
the seminal vesicles, which would prove
important in understanding evolutionarypressures upon these animals (Monge-Nájera, Barquero, & Morera, 2019f), just likehypodermic impregnation, which was firstdescribed by Whitman (1891). Curiously, this decade also produced work on thepresence of corpuscles in the adhesive thatthe animal uses to hunt (Dendy, 1889); theadhesive would remain mostly forgotten as
a study subject for over a century, until it
became a leading-edge subject in the 21st
century (Concha et al., 2015).
The first studies on onychophoran
eggs and hatching (a still poorly known subject) were also written by Dendy (1889) anddiscussed by Fletcher (1891) in these lateyears of the 19th century.
Of particular interest is the fact thateven at this early period, Caribbean onychophorans were so rarely seen that a noteof the “rediscovery” of one was publishedby Grabham and Cockerell (1892), andthat they were included in the reports of“noteworthy findings” by a natural history
club that operated in the island of Trinidad(Anonymous, 1895).
Misidentification of species, still aproblem in 2020, was mentioned as a problem over a century ago by Fletcher (1895)
regarding Australian species. Other papers
followed and dealt with the evolution of theonychophoran body (Goodrich, 1897) andUNICIENCIA Vol. 35, N°. 1, pp. 210-230. January-June, 2021 •The 1870s had a marked increase inproductivity, mostly about anatomy, butalso with a study about the embryology ofPeripatopsis capensis (Grube, 1866) fromSouth Africa (Gegenbaur, 1874) and an early attempt on the evolutionary history of thegroup and its possible relationship with theorigin of insects (Wood-Mason, 1879).

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www.revistas.una.ac.cr/uniciencia •Julián Monge-NájeraUNICIENCIA Vol. 35, N°. 1, pp. 210-230. January-June, 2021 •about the animals, with emphasis on formal
species descriptions. His species descriptions
may be insufficient according to the standardsof the 21st century, but are good if one considers the equipment and resources available
to him at the time, and the fact that Eugène
Louis Bouvier (1856-1944) was a busy man
working mostly on crabs at the time. Son ofa watchmaker, Bouvier moved up the social
ladder through hard work, first as a teacher
in a primary school, then by teaching about
mosses and lichens in a Pharmacy School(Anonymous, 2012). It was only in 1895 that
he got the chair of entomology at the National
Museum of Natural History in Paris; the chair
was previously occupied by Émile Blanchard(who had written the onychophoran section
for the Chilean monograph mentioned earlier;
Anonymous, 2012).
At the museum, Bouvier establishedwhat today would be called a “citizen science” program to enlarge
the collections, and he also
wrote a textbook of natural history for colleges thatcame out at the same time
as his onychophoran monograph. He was then with the
Prince of Monaco expedition, studying deep water
crustaceans from the Sargasso Sea (Anonymous, 2012).
Later in his life, Bouvier wrote popular books
about insect behavior (perhaps under pressure, because he had written little in
the field of insects, despite
keeping the entomology
Fig. 2. Eugène Louis Bouvier, who at the beginning ofchair), but in science he is
the twentieth century wrote the general monograph of thebest remembered for his
phylum Onychophora.
Image source: https://commons.wikimedia.org/wiki/File:Louis_Eug%- studies of crabs and onychophorans, which appeared
C3%A8ne_Bouvier.jpg
their relationships with other invertebrates(Boas, 1898; Packard, 1898).
An unjustly forgotten author, Italianzoologist and alpinist Lorenzo Camerano(1856-1917), published several papers on
the species of Panama and the Andes (e.g.
Camerano, 1896), and around this time wealso find the first papers by French zoologist
Bouvier (Figure 2), the founding father ofmodern onychophorology, who dealt with
their origin, evolution, variation and biogeography (e.g. Bouvier, 1902).
The 1900s started well, with the first paper on spermatogenesis (Montgomery, 1900)
and the first one dealing about population
density (Duerden, 1901). But undoubtedly
what marks this period is the appearance ofa large mass of literature by Bouvier, including evolution (Bouvier, 1902), and his monumental monograph (Bouvier, 1905, 1907),
where he summarized all that was known

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A new look into physiology: 1930
to 1979

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The 1930s had the first papers on Cambrian onychophorans (Hutchinson, 1930;
Walcott, 1931), as well as a study of thelocal variation of a species which showed
that, what appeared to be one species, could
vary in color and in small body characteristics throughout its geographical range(Brues, 1935). A rare report on the parasitesof onychophorans (Vincent, 1936) has not,unfortunately, been followed by much work
afterwards, leaving this as an almost virginterritory for exploration.
This period is marked by the first
papers by authors that would become better known in next decade, such as Marcus
in Brazil and Manton in England (Marcus,
1937; Manton, 1937), as well as by Snodgrass classic work on the compared evolution of onychophoran and arthropod bodies(Snodgrass, 1938).
The decade of 1940 is important because it has the first studies about a region
that would later become a center of onychophoran research, Central America; the articles mostly resulting from strong research
activity in the Panama canal area during,
and after, World War II (Brues, 1941; Dunn,
1943; Clark & Zetek, 1946; Hilton, 1946;
Arnett, 1947).
The 1950s was characterized by articles in popular magazines from London (Hill, 1950), South Africa (Lawrence,www.revistas.una.ac.cr/uniciencia •Julián Monge-Nájera

1922), ventral brain organs (Duboscq, 1920)
and the evolution of the head in relationshipwith other invertebrates (Crampton, 1928).
This period even has a rare Soviet contribution, a general morphology of the brain,
read during the Second Congress of Zoologists, Anatomists, and Histologists of the
USSR (Fedorov, 1927).

UNICIENCIA Vol. 35, N°. 1, pp. 210-230. January-June, 2021 •to have been his real love (Blanckaert &Hurel, 2017).
This is also the decade in which researchers studied how onychophoran bodies process waste (Bruntz, 1903) and did
more comparative studies, considering theparapodia of onychophorans and millipedes(Lankester, 1904); at the same time Sedgwick made the first attempt to associate thesystematic relationships of onychophorans
with their distribution around the world(Sedgwick, 1908a, b). This period included the work of C. E. Porter, in which hetaught the natural history of onychophorans
to students of the Naval Officers School ofChile, his lessons were later collected in the
Chilean Journal of Natural History (Porter,1905) and that probably are not part of thecurriculum in naval schools today.
Their known distribution in Asiaand Oceania was expanded in the decadeof 1910 (Horst, 1910; Annandale, 1912);
a curious observation on the discharge of
mitochondria from the spermatozoon wasreported (Montgomery, 1912) and Clark(1915) analyzed their world distribution,
while the natural history and bibliographyof the Chilean species were reviewed by
two authors (Johow, 1911; Porter, 1917). An
interesting finding from the time was thatthey could also be found in the forest canopy, according to Costa Rican microbiologist
Clodomiro Picado (Picado, 1911).
The 1920s produced the first reportof an onychophoran birth in captivity (forspecimens kept in England: Dakin & Fordham, 1926); and the first study of their diet,from Chile (Janvier, 1928). Bouvier published an “answer to Claude-Joseph” about
Chilean species (Bouvier, 1928), but mostof the work from this period focused on thehead parts of onychophorans: the eye (Dakin, 1921); infra-cerebral organs (Dakin,DOI: http://dx.doi.org/10.15359/ru.35-1.13
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Source Morera-Brenes & Monge-Nájera (2010).

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1976), sarcoplasmic reticulum of smoothmuscle (Heffron, Hepburn & Zwi, 1976),
the sensilla (Storch & Ruhberg, 1977), thesalivary glands (Ruhberg, 1979), and synaptic zones of nephrids (Storch, Alberti, Lavallard, & Campiglia, 1979).
Physiology studies analyzed cuticularchemistry and hardening (Krishnan, 1970);
skeletal collagen (Hepburn & Heffron,1976); enzymic activities of the smoothbody-wall muscle (Heffron, Hepburn, &Zwi, 1977); the presence of monoaminesin the nervous system (Gardner, Robson, &Stanford, 1978), and neuromuscular transmission (Hoyle & del Castillo, 1979).
Attempts were also made to disentangle systematics by comparing isolated aspects, such as locomotion (Manton, 1972),
cuticle (Hackman & Goldberg, 1975), compared anatomy (de la Fuente, 1975) hemolymph (Gowri & Sundara Rajulu, 1976),
and the Golgi complex (Locke & Huie,www.revistas.una.ac.cr/uniciencia •Julián Monge-Nájera

Fig. 3. The electron microscope presents
the onychophoran surface more clearly
than the light microscope and greatly
facilitates taxonomic work. This is an
example from the giant species that lives in
the Caribbean of Costa Rica.

UNICIENCIA Vol. 35, N°. 1, pp. 210-230. January-June, 2021 •1950), New Zealand (Wenzel, 1950), Germany (Zilch, 1955), New York (Milne &Milne, 1954; Alexander, 1958), Philadelphia (Bellomy, 1955), Malaysia (Hendrickson, 1957) and Belgium (Darteville, 1958).
All of these popular accounts highlighted
the use of the adhesive secretion to capture
prey, the strange distribution on the animals
in isolated regions but always within thesame latitudinal belt, and what at the time
was considered as their position as missing
links between annelids and arthropods.
Studies from the period considered
how onychophorans produce leukocytes(Arvy, 1954), “muscle pharmacology” andpossible uses of these animals in pharmacology (Ewer & van der Berg, 1954; Trindade,1958); crural gland microanatomy (Gabe,
1956); brain secretions (Sanchez, 1958;
Mendes & Sawaya, 1958); oxygen consumption in relation to size, temperature and oxygen tension (Mendes & Sawaya, 1958) andthe formation of sperm cells (Tuzet & Manier, 1958; Gatenby, 1959). Perhaps the mostinnovative study from this decade was thefirst biogeographic analysis that explained
the division into two families, as the resultsof historical separation at the time of Gondwana and Laurasia (Vachon, 1954).
In the 1960s, Brazil produced the firststudy of DNA (Simoes, Marques da Silva, &Schreiber, 1964), the first observation withthe electron microscope (Lavallard, 1965),
and detailed studies on molting (Campiglia,
1969). Reassessments of the fossils Xenusion (onychophoran or coelenterate?) and
Aysheaia are also from this period (Tarlo,
1967; Hutchinson, 1969).
The 1970s were characterized by anincrease in anatomical and physiologicalwork. The anatomy of the body wall (Birket-Smith, 1974), giant fibers in the ventral nerve cord (Schürmann & Sandeman,DOI: http://dx.doi.org/10.15359/ru.35-1.13
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An exciting period of unveiled secrets and conservation worries:
1980 to 2020

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www.revistas.una.ac.cr/uniciencia •Fig. 4. Digital reconstructions of fossil
onychophorans (Monge-Nájera &Xianguang, 2002). A: Microdictyon sinicum,
B: Onychodictyon ferox, C: Cardiodictyon
catenulum, D: Hallucigenia fortis, E:
Luoishania lingicruris. Not to scale.

Much study was done in the 1980son the anatomy of onychophorans: musculature and innervation (Hoyle & Williams,
1980); morphometry of the tracheal system(Pereira, Bicudo & Campiglia, 1985); theapplication of scanning electron microscopy to systematics (Read, 1988); and the curious cephalic pits and palps of some Australian species (Ruhberg, Tait, Briscoe, &Storch, 1988).
This period is also marked by the firststrongly evolutionary focus on their reproduction (Morera, Monge-Nájera, & Saenz,
1988; Havel, Wilson, & Hebert, 1989), andseems to also be the first time that onychophorans appear in the IUCN Invertebrate
Red Data Book (Wells, Pyle, & Collins,1983). New possible onychophoran fossils
were reported from Illinois (Thompson &Jones, 1980) and France (Rolfe, Schram,
Pacaud, Sotty, & Secretan, 1982), and thesecond monograph on the family Peripatopsidae (Ruhberg, 1985) was also published inthis period.
The 1990s was characterized by research in genetics and systematics. RNA andDNA sequences were combined with morphological data to assess systematics, using
antennal circulatory organs (Pass, 1991;
de Haro, 1998), and a paper recommended rejection of the “Uniramia” hypothesis,
in which Sidney Manton joined Hexapoda,
Myriapoda and Onychophora as a single
monophyletic group (Wägele, 1993).
Overall, researchers in several regions of the world discovered the large genetic variation hidden in what seemed to bea relatively simple phylum (Grenier, Garber, Warren, Whitington, & Carroll, 1997;
Curach & Sunnucks, 1999; Hebert et al.,
1991; Morera-Brenes, Herrera, Mora, &Leon,1992; Ballard et al., 1992; Briscoe &Tait, 1995; Gleeson, 1996).

UNICIENCIA Vol. 35, N°. 1, pp. 210-230. January-June, 2021 •1977). These attempts had little chance of
succeeding because the resulting phylogenetic trees produced by any particular character were incompatible with the trees produced by other characters.
This is also the time of the first general study about the habitat (Lavallard, Campiglia, Parisi Alvares, & Valle, 1975). Lawrence (1977) summarized research in South
Africa, while Peck (1975) reviewed thespecies of the American continent and Delle
Cave and Simonetta (1975) added new information on the morphology and taxonomic position of the fossil Aysheaia.

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In fossils, publications included the reinterpretation of Hallucigenia, now thought
to be an onychophoran that was originallyinterpreted upside-down by Morris (1977)
and corrected by Hou and Bergström(1991); and the opposite case, a Palaeozoic“onychophoran” reinterpreted as a stalked
echinoderm (Rhebergen & Donovan, 1994).
But perhaps the most unfortunate error of
the time was G. Poinar’s creation of new“onychophoran families” with specimensthat lacked the body parts needed to definefamilies (Poinar, 1996, 2000).
This decade was also marked by the
first “modern synthesis” that proposed evolutionary explanations for the origin of all
known onychophoran characteristics andsummarized their history since the Cambrian, including anatomy, physiology, behavior, distribution, reproduction and systematics (Monge-Nájera, 1995).
The decade of 2000 had an eclectic
production. Papers dealt with how population structure and genetic constitution
are related (Laat, 2006; Santana, Almeida,
Alves, & Vasconcellos, 2008); the rediscovery, after more than a century, of Oroperipatus eisenii in Mexico (Cupul-Magaña &Navarrete-Heredia, 2008); and a revival of
the ancient debate about the origin of headparts (e.g. Eriksson & Budd, 2003; Mayer& Whittington, 2009).
In paleoecology, a quantitative studyof an exquisitely preserved Cambriancommunity from China found similarities
with an extant community in Costa Rica
(Monge-Nájera & Hou, 2000), and experimental taphonomy identified which fossil onychophoran “structures” are real andwhich can be just artifacts (Monge-Nájera
& Xianguang, 2002).
Other reports included the use thehead to insert the spermatophore (Tait &UNICIENCIA Vol. 35, N°. 1, pp. 210-230. January-June, 2021 •The second area of this decade, byproductivity, was ecology and biogeography. Findings from Singapore showed thatrecent introductions could complicate thereconstruction of onychophoran historical biogeography (van der Lande, 1991),
and computerized techniques were used
to understand how climate and paleo-vegetation define their current world distribution (Monge-Nájera, 1994a), as well as
how climate affects body characteristics(Monge-Nájera, 1994b).
This decade was also marked by the
first detailed study of the geographic variation of habitats (Monge-Nájera & Alfaro, 1995), and a model of onychophoran
biogeographic history from the Jurassic
through the Pliocene (Monge-Nájera, 1996).
Other studies were a comparative analysis
of evolutionary trends in onychophorans
and scorpions (Monge-Nájera & Lourenco, 1995), and the first in-depth studies ofthe onychophoran adhesive secretion, withelectrophoresis (Mora, Herrera, & León,
1996); chemical characterization (Benkendorff, Beardmore, Gooley, Packer, & Tait,
1999) and a comparison with arthropod silksecretions (Craig, 1997).
In the field of conservation, the finding of a single large aggregation in New
Zealand (Harris, 1991) and an unconfirmed
estimate that the population of a single species reached millions, led to the unjustified
generalization that these animals “are notrare” (Mesibov, 1998), an error that can leadto dangerous implications for conservation(Monge-Nájera, 1995).
In ethology, this period is marked by
the first experimental study of general behavior (Monge-Nájera, Barrientos, & Aguilar, 1993) and of the pheromonal function of
crural glands (Eliott, Tait, & Briscoe, 1993).

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(Janssen & Budd, 2017); the conserved andderived cell death in embryonic development (Treffkorn & Mayer, 2017); and thereport that fluorescence in situ hybridizationof telomers indicate chromosome fusions(Dutra, Cordeiro, & Araujo, 2018).
In this decade, onychophorans were
found in unexpected places, like Vietnam(Bai & Anh, 2012), lava tubes (Espinasa
et al., 2015) and urban vegetation (Barrett,2013), and the first model to explain andpredict their survival in highly disturbed
habitats, based on their size and habits, waspublished (Monge-Nájera, 2018). The only
tropical African species was collected again
after more than a century (Costa & Giribet,2016), and the period was also marked byadvances in the study of onychophoran genetics and conservation in Brazil (Lacorte,
De Sena Oliveira, and Da Fonseca, 2011;
Costa, 2016; Cunha et al., 2017; Costa etal., 2018).
Costa Rica became the first country to fully map the distribution of its onychophorans and to indicate where they
were preserved and the strength of conservation measures for each species (Morera,Monge-Nájera, & Mora, 2018). The first
field monitoring study covering “several
years” found that the relationship between
onychophoran hunting activity, humidity
and light, was not as expected (Barquero-González, Morera-Brenes, & Monge-Nájera, 2018). Food hiding, parental feeding
investment and ontogenetic diet shift werealso reported for the first time for the whole
phylum (Barquero-González, Vega-Hidalgo, & Monge-Nájera, 2019).
A new branch of Onychophorology was also born in this decade, the Ethnobiology of Onychophorans, with thefirst study of onychophoran representations in folklore and art (Monge-NájeraUNICIENCIA Vol. 35, N°. 1, pp. 210-230. January-June, 2021 •Norman, 2001) and that female-dominatedhierarchies (Reinhard & Rowell, 2005).
This decade was also marked by the
first study of the inflammatory process inonychophorans (Silva, Coelho, & Nogueira, 2000) and the identification of immune
inducible genes (Altincicek & Vilcinskas,2008), but perhaps the most innovative
work was the first study of the physics ofthe adhesive secretion (Jerez-Jaimes & Bernal-Pérez, 2009).
The most recent decade, the 2010s, hasbeen marked by the discovery of the largest species ever and by the first study of themechanism by which onychophorans produce their adhesive “hunting nets” (Morera-Brenes & Monge-Nájera, 2010). The
adhesive skin exudate of some frogs wasfound to be similar to that of onychophorans(Graham, Glattauer, Li, Tyler, & Ramshaw,2013), and the adhesive net mechanism was
finally cracked and found to be produced bypassive hydrodynamic instability (Concha
et al., 2015).
Other studies from this time dealt with
the nanostructures of the solidified adhesive
secretion (Corrales-Urena et al., 2017), theassembling of fibers by electrostatic interactions in phosphoproteins (Baer, Hänsch,
Mayer, Harrington, & Schmidt, 2018), and amimic of onychophoran skin, which is slippery to the adhesive, produced with microporous porphyrin networks (Ryu et al., 2018).
In the field of genetics, the genome
size and chromosome numbers were reviewed (Jeffery, Oliveira, Gregory, Rowell,& Mayer, 2012), and new morphologicalcharacters were added to the arsenal used intaxonomy (Oliveira, Read, & Mayer, 2012).
Other studies dealt with genes related to headand eye development (Eriksson, Samadi, &Schmid, 2013); endoderm marker-genes
during gastrulation and gut-development

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Julián Monge-NájeraAUTHOR CONTRIBUTION
STATEMENTThe total contribution percentage forthe conceptualization, preparation, and correction of this paper was J.M.N. 100 %.

DATA AVAILABILITY
STATEMENTThe data supporting the results ofthis study are fully and freely available
here: https://zenodo.org/record/3698134#.
XmEuBBP0nOQ.

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In these two centuries, Onychophorology has been built by contributions frommany men and women. A few stayed longenough in the field to write numerous contributions (e.g. Barquero-González, Bouvier,Campiglia, Daniels, Mayer, Monge-Nájera,
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paper: the future of Onychophorology will
be born in their minds.

This study was financed by the author.
I thank Carolina Seas and Bernal Morera
for their assistance with format, illustrations and information, and two anonymous
reviewers for valuable recommendations toimprove the manuscript.

www.revistas.una.ac.cr/uniciencia •CONCLUSIONACKNOWLEDGEMENTS
UNICIENCIA Vol. 35, N°. 1, pp. 210-230. January-June, 2021 •& Morera-Brenes, 2015). The period ends
with a series that proposes evolutionary
explanations for several previously unexplained anatomical, physiological, behavioral and ecological characteristics, suchas why onychophoran spermatozoa swim
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names, an idea taken from bird watchers,
to rapidly and cheaply distinguish new onychophoran species until they are formallydescribed (Sosa-Bartuano, Monge-Nájera,& Morera-Brenes, 2018).

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