Taurocletodes, KUNZ, 1975

Karaytuǧ, Süphan & Huys, Rony, 2004, Taxonomic position of and generic distinction between Parepactophanes Kunz, 1935 and Taurocletodes Kunz, 1975 (Copepoda, Canthocamptidae incertae sedis), with description of a new species from the Black Sea, Zoological Journal of the Linnean Society 140 (4), pp. 469-486 : 483-485

publication ID	https://doi.org/ 10.1111/j.1096-3642.2003.00101.x
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scientific name	Taurocletodes
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GENUS TAUROCLETODES KUNZ, 1975

Diagnosis: Canthocamptidae . Small-sized (<0.5 mm). Body robust, more or less cylindrical with prosome slightly wider than urosome. Anal operculum multispinose. Nauplius eye present. Rostrum long, elongate and hyaline. Antennule 6-segmented in ♀, with aesthetasc on segment 3 and as part of acrothek on segment 6; all elements setiform and bare except for posteriormost seta on segment 2; 10-segmented in ♂, with geniculation between segments 7–8. Antenna with allobasis bearing one abexopodal seta; exopod 1- segmented, bisetose. Mandible with 1-segmented palp bearing four setae. Maxillule with two elements on coxa, four on basis; endopod and exopod represented by one and three setae, respectively. Maxilla with three endites. Maxilliped subchelate, syncoxa with strong spine, basis unarmed, endopod drawn out into claw. P1 with 3-segmented rami; exp-2 with small inner seta; enp-2 with long penicillate seta near boundary with enp-1, enp-3 with short penicillate seta near inner distal corner; endopod much longer than exopod. P2–P 4 ♀ short and robust; with 3-segmented exopods and 2-segmented (P2–P3) or 1-segmented (P4) endopods. Exopods with two outer spines on exp-3; P4 exp-3 inner seta absent. Outer spines of P2–P4 exp-1 and -2 enlarged in ♂, that of P3 exp-1 very large. Endopods P2–P3 sexually dimorphic; inner seta of P2 enp-1 absent in ♂; ♂ P3 endopod 3-segmented; drawn out into short apophysis, without inner seta on enp-1. P1– P4 armature formula as follows (apo = apophysis):

Exopod Endopod

The inner seta on P1 exp-2 is minute in T. tumenae . Noodt (1958b) states explicitly that this segment is unarmed in T. dubius but his figure indicates that the inner seta is present.

Fifth pair of legs medially free in ♀, fused in ♂. Exopod and baseoendopod fused in both sexes. Exopodal lobe with four elements in ♀, five in ♂. Endopodal lobe with four setae in ♀, with two spines in ♂. Genital field of ♀ comprising separate gonopores covered by opercula bearing three pinnate spines; sixth legs asymmetrical in ♂, represented by unarmed opercula. Caudal rami about as long as wide; with six setae, setae IV- V well developed .

Type species: Taurocletodes gallicus Kunz, 1975 = Parepactophanes ? dubia Noodt, 1958b = Taurocletodes dubius ( Noodt, 1958b) comb. nov.

Other species: T. tumenae sp. nov.

SPECIES DIFFERENTIATION

It is clear that some of the differences between the type species T. dubius and T. tumenae can be attributed to Kunz’ (1975) imperfect description of the former (as T. gallicus ), which was conceivably based on a damaged specimen. For example, Kunz did not figure the penicillate setae on the P1 endopod nor did he mention them in his supplementary description based on the Azorian material ( Kunz, 1983). His illustration (Abb. 128) shows instead a long plumose seta arising from the distal inner corner of enp-1 whereas in Noodt’s (1958b) description the inner seta is markedly shorter and originating from the middle third of the segment (as in T. tumenae ). The origin of the penicillate seta on enp-2 is difficult to determine when viewed in anterior aspect ( Fig. 5A View Figure 5 ) since it is positioned posteriorly near the proximal margin ( Fig. 5B View Figure 5 ). We therefore assume that Kunz (1975) figured the penicillate seta on enp-2 but had misinterpreted its insertion site and ornamentation. The seta on enp-1 and the penicillate element on enp-3 were overlooked, presumably because they were either missing or concealed by the endopodal segments. Kunz’ (1975) illustration of the male P6 does not refer to that structure but represents the paired cuticular insertion sites of the ventral longitudinal trunk muscles, typically found on the first abdominal somite, posterior to the sixth legs ( Fig. 7B View Figure 7 ).

The available descriptions ( Noodt, 1958b; Kunz, 1975, 1983) do not provide any morphological evidence contradicting the conspecificity of P.? dubia and T. gallicus . Kunz (1983) remarked that the Azorian females lacked the dorsal spinule row found on the caudal rami of the Mediterranean specimens. However, since he drew the innermost spinule on both rami it is more likely that he has overlooked the remaining surface spinules. A second difference noted between both populations concerns the structure of the male P3 endopod but this can be attributed to observation under different angles (cf. Fig. 6B,D View Figure 6 ).

T. tumenae and T. dubius are morphologically very similar, displaying identical armature formulae on the swimming legs and ornamentation patterns on the urosome of both sexes. They can be differentiated by the following characters: (1) relative length of endopodal segments of P1, enp-2 being only half the length of enp- 3 in T. tumenae (equally long in T. dubius ); (2) P4 endopod ♂ shorter than exp-1, with rounded lateral margins, and inner seta shorter than apical elements in T. tumenae (as long as exp-1, with straight lateral margins and inner seta distinctly longer than apical elements in T. dubius ); Kunz (1975) remains vague about the segmentation of the P4 endopod, stating that it is either indistinctly 2-segmented (his Abb. 131 shows a faint suture) or 1-segmented; in the female ( Noodt, 1958b) the endopod is clearly 1-segmented as in both sexes of T. tumenae ; (3) P5 endopodal lobe ♂ with inner spine twice as long as outer one in T. tumenae (outer spine slightly longer than inner one in T. dubius ); (4) P5 exopodal lobe ♂ with second innermost element spiniform and distinctly shorter than adjacent setae in T. tumenae (innermost three elements all setiform and equally long).

PHYLOGENETIC CONSIDERATIONS

Por (1986), in his revision of the family Cletodidae (sensu Lang, 1948), removed Parepactophanes without giving any specific reasons and placed it incertae sedis in the Canthocamptidae . Recent studies have significantly refined the concept of the Cletodidae ( Gee, 1994, 1998, 1999; Gee & Huys, 1996), resulting in the recognition of 17 valid genera: Cletodes Brady , Enhydrosoma Boeck , Limnocletodes , Enhydrosomella Monard , Stylicletodes Lang , Acrenhydrosoma Lang , Monocletodes Lang , Intercletodes Fiers , Kollerua Gee , Schizacron Gee & Huys , Strongylacron Gee & Huys , Triathrix Gee & Burgess , Sphingothrix Fiers , Spinapecruris Gee , Dyacrenhydrosoma Gee , Paracrenhydrosoma Gee , and Neoacrenhydrosoma Gee & Mu.

Neither Parepactophanes nor Taurocletodes fit the revised family diagnosis since: (1) the rostrum is clearly defined at the base (always fused to the cephalothorax in Cletodidae ); (2) the ♀ antennule is 6-segmented (at most 5-segmented in Cletodidae ); (3) the body somites are not separated by constrictions and lack sensillate integumental socles around the posterior margins (always present in Cletodidae ); (4) the distal endopod segment of P 1 in Parepactophanes has an inner lateral seta (= homologue of inner seta on enp- 2 in Taurocletodes ) (inner margin of enp-2 without lateral seta in Cletodidae ).

Additional characters excluding Taurocletodes from the Cletodidae include: (1) the 3-segmented P1 endopod with [1.1.111] formula (at most 2-segmented in Cletodidae with primitively [1.111] formula); (2) presence of an inner seta on P1 exp-2 (and possibly also in Parepactophanes ; absent in Cletodidae ), and (3) the presence of an inner seta on P2–P3 enp- 1 in the female (always absent in both sexes of Cletodidae , enp-1 also being distinctly shorter than enp-2). Finally, the inner seta on P1 enp-1 of both Taurocletodes and Parepactophanes is within the Cletodidae only found in the genus Limnocletodes whose current placement in the family is provisional ( Gee, 1998).

Gómez Noguera & Fiers (1997) recently expressed an urgent need for revision of the Canthocamptidae , suggesting that this will eventually lead to the exclusion of the genera Mesochra Boeck and Amphibiperita Fiers & Rutledge from that family. Although the authors do not present specific arguments for their statement, it is conceivable that it was partly based on the detailed morphology of the male P3 endopod which they regarded as particularly distinctive because of the distad displacement of the vestigial inner setae. Such a character has potential phylogenetic significance but, as for many other sexually dimorphic character states, its utility is limited since some taxa have secondarily lost the inner setae on P3 enp- 2 in the female (and concomitant with this the sexual dimorphism in the male), thereby obscuring phylogenetic relatedness. This limitation is illustrated in both Taurocletodes and Parepactophanes where the inner margin of P3 enp-2 is unarmed in the female.

Within the primarily freshwater Canthocamptidae there is a core group of genera confined to marine and brackish water habitats, comprising Mesochra , Amphibiperita , Psammocamptus Mielke , Bathycamptus Huys & Thistle (synonymized with the former by Mielke (1997) but reinstated by George & Schminke (2003)), Mesopsyllus and Isthmiocaris George & Schminke. Members of this group share the reduced morphology of the male sixth legs, being represented by membranous flaps completely lacking in armature elements. In the females the sixth legs closing off the genital apertures bear 1–3 setae, indicating a different ontogenetic trajectory between the sexes. The same sexual dimorphism is also encountered in Taurocletodes ( Fig. 9C View Figure 9 ) and most likely (although unconfirmed at present) also in Parepactophanes . In most freshwater canthocamptids the male sixth legs typically bear two or three well developed setae (e.g. Dussart, 1967; Hamond, 1987).

The genera Hemimesochra , Poria Lang , Perucamptus Huys & Thistle and Pusillargillus Huys & Thistle are known from females only but show close similarity in mouthpart morphology with Bathycamptus , Mesopsyllus and Psammocamptus , and by inference, are also regarded as representatives of the group above (named here the Mesochra -group for practical, but not necessarily phylogenetic reasons). Other marine genera such as Pholetiscus Humes , Ophirion Por , Itunella Brady , Dahlakia Por , Heteropsyllus , Nannomesochra Gurney and Cletocamptus have well developed sixth legs in the males, show numerous additional discrepancies in the mouthparts and swimming legs, and almost certainly represent at least two different evolutionary lineages, not directly related to the Mesochra -group. Within the latter, Taurocletodes and Parepactophanes appear to be most closely related to Mesochra , but precise phylogenetic inferences cannot be drawn at present because the genus is not a natural unit ( Gómez Noguera & Fiers, 1997) and possibly polyphyletic.

One character that is potentially indicative of phylogenetic affinity between Parepactophanes / Taurocletodes and the Mesochra complex is the peculiar arrangement of the dorsal sensillae on the thoracic somites bearing legs 4–6. In both sexes of T. tumenae the two dorsal sensillar pairs are very closely set together with typically one in a slightly more anterior position ( Figs 2A View Figure 2 , 7A View Figure 7 ). A similar displacement of the dorsal sensillae was also illustrated by Gómez Noguera & Fiers (1997) in two species of Mesochra ; however, the level of detail contained in most other species descriptions does not enable us to extrapolate this to the whole genus (but confirmed in M. rapiens (Schmeil, 1894) , M. pygmaea (Claus, 1863) , M. lilljeborgi Boeck, 1865 and M. heldti Monard, 1935 ; pers. observ. by RH).

The close relationship between Parepactophanes and Taurocletodes is indicated by the following derived character states: (1) antennule ♀ 6-segmented with aesthetasc on segment 3; (2) antennary exopod 1-segmented and bisetose; (3) mandibular palp 1-segmented with four setae, all arising subapically; (4) robust and short P2–P4; (5) absence of inner exopodal setae on P2–P4 (except for P4 exp- 3 in P. minuta ); (6) P5 with fused exopod and baseoendopod in both sexes, and possibly (7) P 6 ♂ without armature elements. Some of these, such as the antennulary segmentation and the condition of the male P6, may be synapomorphies diagnosing a wider group of taxa, but the remaining characters leave little doubt about their sistergroup relationship.

Parepactophanes displays a number of autapomorphies distinguishing it from Taurocletodes : (1) P1 endopod 2-segmented (fusion of enp-2 and -3); (2) P1 exp-2 without inner seta (although this would require confirmation considering its minute size in Taurocletodes ); (3) P2–P4 exp-3 with only one outer spine; (4) endopod P2–P3 1-segmented. Unique autapomorphies defining Taurocletodes include the penicillate setae on the P1 endopod (and the extreme proximad displacement of the inner seta on enp-2) and the marked sexual dimorphism on the swimming leg exopods (in particular P3 exp-1). The enlarged spine on P3 exp- 1 in the male bears a remarkable similarity to the massive outer spine reported in the male of Amphibiperita tropica (Jakobi, 1956) ; however, in the latter it is found on P4 exp-1 ( Fiers & Rutledge, 1990) and consequently is not serially homologous.