Cristacoxidae George 2002

Monophyly of Cristacoxidae sensu George (2002)

Although George’s (2002) assessment of the position of Laophontisochra was hampered by the absence of males, the evidence supporting his assignment of the genus to the Cristacoxidae was nevertheless weak. Both Laophontisochra and Acuticoxa have a radically divergent morphology, exhibiting only four (7, 9, 10, 11) of the 12 female cristacoxid autapomorphies listed above. At least for some of these the question arises whether the apomorphic state observed is homologous to the typical cristacoxid condition: the inner basal spine/seta of P1 is displaced onto the anterior surface of the basis (character 7), P2–P4 exp-2 has lost the inner seta (character 9; however, the homologue of exp-2 is not expressed as a discrete segment, but its outer spine is), P2–P4 exp-3 has only two outer elements instead of three (character 10; however, these elements are not typically elongate and setiform as in Noodtorthopsyllus and Cubanocleta), and P3–P4 endopods 1-segmented (character 11: the validity of this character is difficult to assess since the endopods are either lost (P 3 in Laophontisochra) or represented by a small unisetose segment).

George (2002) advocated a basal split of the Cristacoxidae into two lineages, i.e. a clade uniting the “more derived” traditional cristacoxid genera (Cristacoxa, Noodtorthopsyllus, Cubanocleta) and a “more plesiomorphic” clade comprising Laophontisochra (and by inference, Acuticoxa). The sistergroup relationship (and therefore the monophyly of the family) was based on three character states, i.e. (1) the presence of cristae on the coxa of P1, (2) large maxillipeds, and (3) “atrophy of antennary exopod and abexopodal seta”. Each of these character states leave room for interpretation. Noodtorthopsyllus and Cubanocleta have paired serrate crests on the coxa and a single one on the praecoxa of leg 1, in addition to serially homologous crests on the coxae of P2 and P3 and occasionally a lobate outgrowth on the coxa of P4. In Acuticoxa and Laophontisochra a single non-serrate, lobate or spinous outgrowth (not a genuine crest!) is present on the coxa of P1 but no such structure is discernible on the praecoxa. Serially homologous spinous projections are also present on the coxae of P2–P4 of Acuticoxa but not in Laophontisochra. The single pointed projection on the P1 coxa in Acuticoxa clearly does not resemble the paired serrate cristae exhibited by Noodtorthopsyllus and Cubanocleta and is probably the result of convergent evolution. Secondly, the maxillipeds are fundamentally different between Laophontisochra - Acuticoxa (L-A) and Noodtorthopsyllus - Cubanocleta (N-C). In the former two genera the syncoxa is unarmed and the endopod is represented by a geniculate claw bearing a minute accompanying seta along its outer margin (secondarily lost in A.

biarticulata); in the latter the syncoxa has a pinnate seta and the endopodal claw is not geniculate, bearing a short accompanying seta along the outer margin and, more distally, a distinct long seta along the inner margin. Given these morphological differences, using maxillipedal size as evidence in support of a sistergroup relationship between L-A and N-C appears a weak argument. Finally, adult cristacoxids consistently lack the antennary exopod (its former position in copepodid I is indicated by a membranous insert in the adult) and the abexopodal seta on the allobasis. Such consistency is not observed in Laophontisochra or Acuticoxa where the “atrophied” condition prevails, with the antennary exopod being absent (A. ubatubaensis) or represented by a seta (L. maryamae) or a minute unisetose segment (A. biarticulata), and the abexopodal seta being lost only in L. maryamae. George (2002) pointed out that including Laophontisochra in the Cristacoxidae would draw the family to a much more basal position in the Laophontoidea because of certain primitive characters displayed by L. maryamae such as the presence of two basal setae on the mandibular palp, a character thus far only reported from some primitive Laophontidae (subfamily Esolinae; cf. Huys & Lee 2000) and effectively excluding both Acuticoxa and Laophontisochra from the clade [Adenopleurellidae + Orthopsyllidae + Laophontopsidae + Cristacoxidae]. Two of the cristacoxid autapomorphies mentioned above (characters 1 and 13) cannot be verified in either Laophontisochra or Acuticoxa since they are based on male character states. However, the recent discovery of a closely related genus from Paranaguá Bay (Brazil), represented by both sexes (named hereafter “Genus X”), showed that neither the spermatophore nor the P3 sexual dimorphism are of the cristacoxid type (P.H.C. Corgosinho & M. Büntzow, pers. commn), and that the male sixth legs bear 3 setae (except for the basal Normanellidae all other laophontoidean families have 2 setae; cf. Huys & Lee 1998 /99). Neither Acuticoxa nor Laophontisochra have setiform outer elements on the distal exopod segment of P2–P4. The absence of this character would place these genera outside the clade [Laophontopsidae + Cristacoxidae]. Although the males of both genera are unknown, the male of the closely related “Genus X” shows that the segments distal to the geniculation in the male antennule are free. The presence of a single compound segment distal to the geniculation is a synapomorphy uniting the Laophontopsidae and Cristacoxidae.

The coxal projections on legs 1–4 in Laophontisochra and Acuticoxa may be indicative of a relationship with some genera currently included in the Huntemanniidae. Por (1986a: 421) established the family Huntemanniidae for the genera Nannopus Brady, 1880, Huntemannia Poppe, 1884 [type], Pontopolites T. Scott, 1894, Metahuntemannia Smirnov, 1946, Beckeria Por, 1986b and possibly Pseudocletodes Scott & Scott, 1893. Unfortunately, it has remained unnoticed that Brady (1880: 100) had already established a new subfamily Nannopinae within the Harpacticidae for Nannopus Brady, 1880 (type genus) and Platychelipus Brady, 1880 (now placed in the Laophontidae). According to the Principle of Coordination applied to familygroup names (ICZN Art. 36.1) Brady (1880) is deemed also to have simultaneously established the coordinate family name Nannopidae. Since the family-group name Huntemanniidae was used by Por (1986a) to include the genus Nannopus, it must sink as a junior synonym of Nannopinae Brady, 1880. Huys (2009) pointed out that the second part of the generic name Nannopus is derived from the Greek stem Oυς, meaning foot, and hence the family name must be corrected to Nannopodidae. Since Por’s (1986a) proposal, Dahms and Pottek (1992) have relegated Beckeria to a junior subjective syonym of Metahuntemannia, Kihara and Huys (2009) have assigned Pseudocletodes to the Normanellidae and two genera have been added to the family, Rosacletodes Wells, 1985 and Pottekia Huys, 2009. The former was proposed by Wells (1985) as a new replacement name for the cletodid genus Echinocletodes Pallares, 1982 (type species E. kuehnemanni Pallares, 1982), a junior homonym of Echinocletodes Lang, 1936 (type species Cletodes armata T. Scott, 1903; cf. Huys et al. 1996a: 75), and is of particular interest here. Bodin (1997) did not assign the genus to any of the families defined by Por (1986a) while George (2008) considered A. kuehnemanni (Pallares, 1982) a species incertae sedis in the Argestidae. Both Huys et al. (1996a) and Wells (2007) listed it as a genus in the Huntemanniidae.

Pallares’ (1982) description of Rosacletodes kuehnemanni, based on material from Tierra del Fuego (Argentina), clearly shows spinulose projections on the coxae of P1–P4 which are virtually identical to the structure found on the coxa of P 1 in L. maryamae. Such structures were also recently described for Huntemannia jadensis Poppe, 1884 by Kornev and Chertoprud (2008). There is also a gross resemblance in the general morphology of the swimming legs (P2–P4) between Rosacletodes and Laophontisochra, including the strongly reduced endopods (represented by a single seta in Rosacletodes) and exopods (at most 2- segmented in the Ƥ), the enlarged outer spine on P2–P4 exp-1 (proximal outer spine if only one segment expressed), and the outer basal seta originating from an articulated setophore (this is shown for at least P4–P 5 in R. kuehnemanni and L. maryamae and has as yet to be confirmed for P2–P3). Additional similarity is found in the plesiomorphic condition of the mandibular palp (2-segmented, 2 basal setae, exopod represented by single seta, endopod by 3) and the apomorphic reduction of caudal ramus seta V. Rosacletodes shows several plesiomorphic character states not found in Laophontisochra or Acuticoxa such as the 5-segmented Ƥ antennule (with aesthetasc on segment IV), the trisetose antennary exopod and the biramous Ƥ P5 with six elements on the endopodal lobe and five on the exopod. Prehensility of the P1 endopod as displayed in the nannopodid genera Laophontisochra and Acuticoxa is a morphological adaptation that has evolved secondarily and convergently in response to changing environments in many other harpacticoid families such as the Ectinosomatidae (e.g. Hicks & Schriever 1983), Pseudotachidiidae (e.g. Hicks 1988), Cylindropsyllidae (e.g. Huys & Willems 1993) and Leptastacidae (Huys et al. 1996b). The non-prehensile P1 endopod in Rosacletodes has an identical segmentation and armature pattern as that of the prehensile ramus in both Laophontisochra and Acuticoxa, the only difference being the much shorter proximal endopod segment in Rosacletodes. Prehensility of the P1 endopod is here considered a synapomorphy (in conjunction with the 4- segmented Ƥ antennule, reduced antennary exopod, geniculate endopodal claw on the maxilliped, etc.) supporting the sistergroup relationship between Laophontisochra and Acuticoxa within a larger encompassing clade characterized by coxal projections on the swimming legs. This clade further includes Rosacletodes, Huntemannia and “Genus X”, all of which show varying degrees of coxal modification in leg 1, being most extreme in the latter genus (P.H.C. Corgosinho & M. Büntzow, pers. commn). Based on the arguments presented above, Laophontisochra and Acuticoxa are here formally assigned to the Nannopodidae.

The family Nannopodidae is heterogeneous at present; in particular, both Metahuntemannia and Pottekia (= Talpina) are radically divergent from the other nannopodid genera. The sexual dimorphism expressed on the P4 endopod (distal inner seta of Ƥ modified into a serrate curved spine in 3; cf. Pottekia pectinata (Dahms & Pottek, 1992)) clearly indicates an affinity with genera such as Bathycamptus Huys & Thistle, 1989; Micropsammis Mielke, 1975; and Isthmiocaris George & Schminke, 2003 (and almost certainly the closely related Perucamptus Huys & Thistle, 1989 – male unknown at present!) (George & Schminke 2003; Huys & Thistle 1989; Mielke 1975), all of which are currently assigned to the subfamily Hemimesochrinae in the Canthocamptidae (Wells 2007). Pending a revision of the latter family, Metahuntemannia and Pottekia are here tentatively assigned to the Hemimesochrinae.