European Journal of Protistology 91 (2023) 126036

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European Journal of Protistology
journal homepage: www.elsevier.com/locate/ejop

Copterus tyloloricatus (Ciliophora, Suctorea), a new suctorian genus
and species
Igor Dovgal a, *, Atsushi Yamaguchi b, Daiki Kojima b, Yoshinari Endo caA.O. Kovalevsky Institute of Biology of the Southern Seas of RAS, Sevastopol, Russia
Faculty of Fisheries, Hokkaido University, Hakodate, Japanc
3-28-1, Katsura, Izumi-ku, Sendai, Japanb

A R T I C L E I N F O

A B S T R A C T

Keywords:
Calanoid host
Copterus gen. n.
Copterus tyloloricatus sp. n.
Epibiosis
Suctorian ciliates

We present the description of the new suctorian genus Copterus gen. n. with type species Copterus tyloloricatus sp.
n. from the family Acinetidae, inhabiting the prosomes and urosomes of calanoid copepods from the northern
North Pacific Ocean. The new taxon is characterized by (i) an ellipsoidal to triangular, asymmetric, dorsoven­trally flattened cell body, which lies horizontally on the lorica surface; (ii) an unflattened lorica; and (iii) the
presence of three to five radially arranged bundles of tentacles positioned at the edge of the body or on
actinophores.

1. Introduction
The suctorians are a rather species-rich group of ciliates. For
example, Dovgal (2002a) listed 531 species and the majority of theseciliates are commensals of various aquatic invertebrates or vertebrates(Chatterjeee and Dovgal, 2020; Chatterjee et al., 2021a; Dovgal, 2002a,
2013; Jankowski, 2007; Mikac et al., 2020). The identification of suc­torians is mainly based on the morphology of trophont stages because
the swarmers are unknown in most species. Useful morphologicalcharacters include the tentacles and actinophores, adhesive organelles,
loricae and macronuclei as well as the shape of cell body (Dovgal, 2013).
A novel epibiotic suctorian ciliate, which differs from the known
species by the shape of body and arrangement of actinophores, wasfound during the investigation of epibiotic relations between calanoid
copepods and suctorians collected in the northern North Pacific Ocean(Fig. 1).
This species was observed on prosomes and urosomes of the calanoid
copepods Paraeucheta birostrata Brodsky, 1950, P. elongata (Esterly,1913) (Fig. 2), and Heterorhabdus tanneri (Giesbrecht, 1895) collectedfrom 0 to 2000 m at several stations located at 47◦ N, 159◦ E to 47◦ N,
179◦ W in the central subarctic Pacific.
The species is a loricate suctorian ciliate having three to five bundlesof capitate tentacles, positioned on the edges of the body, or at actino­phores. In addition, the endogenous budding was observed in two in­dividuals, which, along with the presence of lorica and arrangement of

the tentacles in bundles, permits to assign the species to the family
Acinetidae Ehrenberg, 1838. However, having three to five bundles oftentacles and a dorsoventrally flattened cell body, the species suffi­
ciently differs from representatives of the related genera Acineta
Ehrenberg, 1834 and Phyllacineta Jankowski, 1978. Hence the foundsuctorian can be assigned to a new genus and species.
2. Material and methods
2.1. Sampling, terminology
Zooplankton samples were collected by vertical tows from 2000 m tothe surface with three different net systems: (1) a ring net with a mouthdiameter of 80 cm and mesh width of 335 μm, (2) a Quad-NORPAC net
with mesh widths of 63 μm and 335 μm (Hama et al., 2019), and (3)VMPS (Vertical Multiple opening and closing Plankton Sampler (Ter­azaki and Tomatsu 1997)) with a mesh width of 63 μm. The new species
was collected at four stations (St. A–D) in the central subarctic Pacificlocated at 46◦ 33′N, 159◦ 13′E (St. A) on 25 July 2021; at 47◦ 00′N,
160◦ 01′E (St. B) on 26 July 2021; at 47◦ 00′N, 176◦ 06′E (St. C) on 2
August 2021; and at 46◦ 59′N, 179◦ 26′W (St. D) on 3 August 2021
(Fig. 1). Collected samples were preserved with 5% formalin seawater.
The copepod specimens infested with suctorian ciliates were sorted
under a stereomicroscope (Leica M165C). Ciliate pictures and mea­
surements were taken using a Leica MC170 mounted on Leica M165C-* Corresponding author at: A.O. Kovalevsky Institute of Biology of the Southern Seas of RAS, Nakhimov ave., 2, 299011 Sevastopol, Russia.
E-mail address: dovgal-1954@mail.ru (I. Dovgal).
https://doi.org/10.1016/j.ejop.2023.126036
Received 15 June 2023; Received in revised form 18 November 2023; Accepted 19 November 2023
Available online 20 November 2023
0932-4739/© 2023 Elsevier GmbH. All rights reserved.

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European Journal of Protistology 91 (2023) 126036

Ergo/MCI-HH/1 as well as the program Toup View 3.7 for digital
camera.
For the taxonomy of suctorian ciliates we mainly followed Dovgal(2013). For terminology, see Dovgal (2002a).

irregular wrinkles. Stalk thin, robust, transparent, distinctly demarcatedfrom the bottom of lorica, with length the same or a little longer thanlorica, adhesive disk not observed.
Etymology. The species-group name ‘tyloloricatus’ is a composite of
the Greek noun τύλος – ‘tylos’ (callous, bubble) and the Latin adjective‘loricatus’ (armored, loricate) and refers to the characteristic, unflat­
tened, bubble-shaped, lorica in the new species.
Type material. The type slide and two paratype slides have been
deposited in Protist Collection of the Natural History Museum (London,
UK). The registration number for the type slide is 2023.6.8.1. Paratypeslides numbers are 2023.6.8.2 and 2023.6.8.3.
Type locality. Central subarctic Pacific, 46˚33′N, 159˚13′E (St. A).
Other localities. Central subarctic Pacific, 47˚00′N, 160˚00′E (St. B),
47˚00′N, 176˚05′E (St. C), and 46˚59′N, 179˚26′W (St. D).
Type host. Paraeuchaeta birostrata Brodsky, 1950 (Crustacea,
Copepoda, Calanoida).
Other hosts. Female Paraeuchaeta elongata (Esterly, 1913); female
Heterorhabdus tanneri (Giesbrecht, 1895).
Localisation on the host body. Prosomes and urosomes.
Morphology. Cell body asymmetric, dorsoventrally flattened, lies
horizontally on lorica (Fig. 3A–E). Body length from a top view 40–95
μm, body width 41–103 μm, body thickness from a lateral view 22–32
μm in vivo (n = 6). Actinophore length from a top view 17–39 μm,
actinophore width at the base 16–37 μm (n = 6). Lorica globular,transparent, unflattened, thin-walled, from a lateral view 76–152 μm
long, 74–160 μm wide (n = 4). Usually, a conical invagination is present
at the base of the lorica, at the top of which the stalk is connected withthe lorica (Fig. 3A, C, E). Stalk thin, robust, transparent, distinctly
demarcated from the bottom of lorica, 55–134 μm long and 6–10 μm
across (n = 4). Macronucleus ellipsoid, centrally located, 15–20 μm long(n = 6). Fifty to 70 thin clavate tentacles arranged in each of groups at
surface of hemispherical actinophores or directly on the cell body.
Tentacles 23–39 μm long (Table 1). Three to five radially arranged
bundles of tentacles, positioned on actinophores in some individuals(Fig. 3B, C, E), while placed on edge of cell body in others (Fig. 3D). In
some individuals, tentacles located both on body and on actinophores(Fig. 3B).

2.2. ZooBank registration
Present work: urn:lsid:zoobank.org:pub 45A6326B-0541-4C65846E-F289CD9AD039.zoobank.org
Copterus gen. n.:
Copterus tyloloricatus sp. n.:urn:lsid:zoobank.org:act 53E65FF7AC76-49F5-B87A-4FD5F3520057.zoobank.org
3. Results
Suctorea Claparède & Lachmann, 1859.
Endogenia Collin, 1912.
Acinetida Raabe, 1964.
Acinetidae Ehrenberg, 1838.
3.1. Copterus gen. n.
Diagnosis. Acinetid with flattened, horizontally oriented cell body
positioned on top part of lorica, assigned with three to five radially ar­ranged bundles of tentacles positioned at the edge of the body or on
actinophores. Macronucleus ellipsoid, centrally located. Lorica unflat­
tened. Reproduction by endogenous budding by forming a single tomitein brood pouch.
Etymology. Copterus (masculine, originated from English ‘copter’)reflects the characteristic, “drone-like” shape of ciliate cell body, whichis flattened, horizontally oriented, provided with up to five radially ar­ranged actinophores.
Type species. Copterus tyloloricatus sp. n.
Species assigned. Copterus tyloloricatus sp. n.
3.2. Copterus tyloloricatus sp. n. (Fig. 3A–E; Table 1)
Diagnosis. Cell body from a lateral view dorsoventrally flattened,
lies horizontally on the lorica, from a top view triangular to ellipsoidal,
some asymmetric. Fifty to 70 thin clavate tentacles per bundle. In some,possible young individuals actinophores might not have developed but
three bundles of tentacles present (Fig. 3D). Macronucleus 15–20 μm
long. Lorica globular, transparent, thin-walled, with numerous small

4. Discussion
4.1. Classification of Copterus gen. n. and comparison with related genera
The similar polymerization of the tentacle fascicles positioned on

Fig. 1. Map of the collection sites.
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European Journal of Protistology 91 (2023) 126036

In small individuals with only three bundles of tentacles, actinophores
seem to be undeveloped (Fig. 3D). In addition, in some ciliate in­dividuals the tentacle fascicle is positioned just on the body, as well as at
the actinophores (Fig. 3B).
It is still unknown whether the polymerized tentacle bundles oractinophores form simultaneously or sequentially during suctorianmetamorphosis. However, it is our point that the simultaneous presenceof the bundles of tentacles both on cell body and on actinophores introphonts of C. tyloloricatus suggests successive formation of the latter inthe species. This leads us to conclude that such variability reflects thepresence of different developmental stages in C. tyloloricatus, as
observed in A. euchaetae (Chatterjee et al., 2021b; Santhakumari, 1985;
Sewell, 1951).
In such a case the two stages of C. tyloloricatus development might beclassified. The body width at the first stage (Fig. 3D) was 41–64 µm, withthree bundles of tentacles. The cell body in some cases was triangular,
with actinophores not developed. The reproduction at this stage was notobserved. The body width at the second stage (Fig. 3B, C, E) was 89–103µm, with three to five bundles of tentacles and some of them positioned
at actinophores (the additional bundles of tentacles directly on the body
could also be observed, Fig. 3B), the cell body became disc-shaped. The
reproduction was observed at this stage.

radially arranged actinophores is characteristic for representatives of thegenera Asterifer Jankowski, 2007 and Leboransia Dovgal, 2002 (Dovgal,
2002a; Jankowski, 2007). However, the species of the above-mentioned
genera do not have a lorica. In addition, in both genera exogenous
budding forming of unciliated swarmers (vermigemmy) was observed(Dovgal, 2002a; Jankowski, 2007), whereas we observed endogenous
budding in the new genus (Fig. 3B).
A similar shape of the lorica was observed in some suctorians withexogenous budding, for example, Paracineta sp. (Curds, 1987; Dovgal,
2002b). However, we assigned the observed species to the family Aci­
netidae because of the endogenous mode of budding.
The new genus differs from Acineta Ehrenberg, 1833 by more bun­dles of tentacles (3–5 vs. 2). It differs from Phyllacineta Jankowski, 1978by dorsoventrally instead of laterally flattened body and by moretentacle fascicles (up to five vs. 3; Curds, 1985; Dovgal, 2002a).
It should be mentioned that the presence of three or fewer bundles offascicles of tentacles was indicated in the diagnoses of the Acinetidae(Dovgal, 2002a, 2013; Lynn, 2008). Hence, the suitable amendment of
the family diagnosis is necessary.
4.2. Comparison of Copterus tyloloricatus sp. n. with similar species
The new species resembles the acinetid Acineta euchaetae Sewell,1951 (Sewell, 1951), an epibiont of calanoid copepods by the presenceof a dorsoventrally flattened cell body but it differs from the latter aswell as from A. arcachoniensis Fernandez-Leborans et Tato-Porto, 2000
(Fernandez-Leborans and Tato-Porto, 2000) by the presence of three tofive fascicles of tentacles, positioned on actinophores (Table 1). In turn,the new species differs from Phyllacineta jolyi (Maupas, 1881) collectedfrom marine algae, bryozoa and hydrozoan and P. tripharetrata (Entz,
1902) collected from freshwater planktonic crustaceans by the presenceof dorsoventrally, instead of laterally, flattened body and a lorica, which
does not cover the cell body (Table 1; Curds, 1985; Maupas, 1881).

4.4. Ecological features
Probably, a flexible lorica characteristic for the species creates ability(in addition to the flexible stalk) to deflect the body with increasinghydrodynamic loads in the direction to the conjunction between stalkand lorica, thereby reducing the load influence (Chatterjee et al., 2021b;
Dovgal, 2002b; Dovgal and Kochin, 1997).
The investigated suctorians were found to be attached only to thefemale copepods, which is quite consistent with the previous observa­
tions on other suctorian species (Endo et al., 2022; Sedlacek et al.,2013). It is pointed out that this is related to a larger size and a longer life
span of adult female calanoids compared to male copepods (Endo et al.,2022).

4.3. Developmental stages of Copterus tyloloricatus sp. n.
We observed different numbers of tentacle bundles in C. tyloloricatus.

Fig. 2. Localization of Copterus tyloloricatus sp. n. (white arrow) on the copepod Paraeuchaeta elongata.
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European Journal of Protistology 91 (2023) 126036

Fig. 3. A–F. Morphology of Copterus tyloloricatus sp. n. (in vivo). A – schematic drawing of Copterus tyloloricatus sp. n.; B – a budding individual with three acti­
nophores and two additional bundles of the tentacles; C – specimen with five actinophores; D – two young individuals with three bundles of tentacles; E – lateralview. add – additional bundles of tentacles; BPch – brood pouch; Ma – dividing macronucleus.

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European Journal of Protistology 91 (2023) 126036

Table 1Comparison of morphological characteristics of Copterus tyloloricatus sp. n. and some other suctorian ciliate species.
Charactera

SpeciesAcineta euchaetae

Acineta euchaetae

Acinetaarcachoniensis

Phyllacineta jolyi

Phyllacineta
tripharetrata

Copterus tyloloricatus
sp. n.

No. of fascicles of tentacles
Actinophore presence /absence
Tentacle number per
actinophore (or fascicle)
Body length
Body width
Macronucleus length
Lorica length
Lorica width
Stalk length
Stalk diameter
Actinophore length
Actinophore width
Tentacle length
Body shape2
Absent2
Absent2
Present3
Absent3
Absent

3–5
Present / absent at
early stages
23–57

41
75
26

71
104

45
115

153
13
25
20
30
Oval, laterally
flattened

180
2

10

Rhomboid, laterally
flattened

Triangular, laterally
flattened

Spherical
Maupas (1881)

Oval
Curds (1985)

40–95
41–103
15–20
76–152
74–160
55–134
6–10
17–39
16–37
23–39
Triangular to oval,
dorsoventrally
flattened
Ellipsoid
Present study

Macronucleus shape
Referencea

15–75
33–125

35–52
50
90

125–154
22–25

Globular,dorsoventrally
flattened
Ribbon-likeSewell (1951)

36
Elongated,dorsoventrally flattened

C-shaped
Irregular ellipsoid
Femandez-Leborans and Tato-Porto (2000)

Measurements in µm.

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Igor Dovgal: Conceptualization, Writing – original draft, Writing –review & editing, Supervision, Funding acquisition. Atsushi Yama­guchi: Data curation, Investigation, Resources. Daiki Kojima: Investi­
gation. Yoshinari Endo: Project administration, Writing – review &editing.
Declaration of Competing Interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
Data availability
Data will be made available on request.
Acknowledgments
Authors greatly appreciate Dr. Hiroshi Kajihara (Hokkaido Univer­sity) for his help with the resolution of the nomenclature issue and Dr.
Jesús S. Hernández-Orts (Natural History Museum) for his help withdepositing of the type material. Comments from the editor and two
anonymous referees greatly improved the quality of our manuscript. The
Igor Dovgal’s work was conducted in the framework of the state as­signments of the A.O. Kovalevsky Institute of Biology of the Southern
Seas of RAS (N◦121040500247–0).
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