Inermipes Lee & Huys, 2002

Karanovic, Tomislav & Hancock, Peter, 2009, On the diagnostic characters of the genus Stygonitocrella (Copepoda, Harpacticoida), with descriptions of seven new species from Australian subterranean waters 2324, Zootaxa 2324 (1), pp. 1-85 : 41-43

Genus Inermipes Lee & Huys, 2002

Diagnosis emended. Relatively large and not very slender Ameiridae , with cylindrical habitus and no distinct demarcation between prosome and urosome, although body constricted at first urosomite. Integument weakly chitinized and without cuticular windows; hyaline fringe of all somites smooth. First pedigerous somite incorporated into cephalothorax. Prosome weakly ornamented with very large sensilla, urosome additionally ornamented with ventral rows of spinules. Genital double-somite without visible suture but slightly constricted laterally; genital field with single large copulatory pore, wide and extremely short copulatory duct and two semicircular seminal receptacles; single small genital aperture covered by fused reduced sixth legs, without armature or ornamentation. Anal operculum wide and convex, not reaching to posterior end of anal somite, ornamented with many more spinules near posterior margin. Caudal rami conical, as long as greatest width and slightly divergent; dorsal seta inserted near posterior margin and very close to inner margin, about twice as long as ramus; proximal lateral seta arising somewhat dorsolaterally at middle; distal lateral seta arising at 5/6 and laterally; inner apical seta smaller than ramus; principal apical setae pinnate, with breaking plane. Antennula long and slender, eight-segmented in female and ten-segmented but not strongly geniculate in male; without seta on first segment. Antenna composed of coxa, basis, two-segmented endopod and onesegmented exopod; exopod minute, armed with single apical seta. Labrum with wide and nearly straight cutting edge. Mandibula with narrow cutting edge and two-segmented palp; basis unarmed, endopod with four apical setae. Maxillular endopod absent. Maxilla with single endite on syncoxa; endopod minute, armed with two setae. Maxilliped three-segmented, unarmed. All swimming legs with three-segmented exopod. Endopod of first leg three-segmented, that of other legs one-segmented. First exopodal segment of all legs much longer than any other segments and without inner seta; second exopodal segment of first leg without inner seta, that of other legs with inner seta; third exopodal segment of all legs with two outer spines and no inner setae, except in fourth leg where one inner seta present. First endopodal segment of first leg larger than other two endopodal segments but smaller than first exopodal segment, armed with spiniform inner seta; endopodal segment of other legs very small, that of second and fourth legs armed with single apical spine, that of third leg with inner apical seta and outer apical spine. Basis of first leg in male with inner spine transformed, smooth and inflated distally; no other sexual dimorphism in swimming legs. Fifth leg similar in both sexes, with baseoendopod almost completely fused to somite and represented only by outer basal seta; exopod a minute but distinct segment, armed with single apical seta in female and (normally) with additional inner seta on male right leg. Sixth legs in male fused basally together and to somite, without armature or ornamentation.

Type and only species. Inermipes humphreysi Lee & Huys, 2002 .

Remarks. This Western Australian genus is apparently very closely related to Megastygonitocrella gen. nov., with its identical armature and segmentation of the swimming legs (the endopod of the second to fourth legs are one-segmented, with the respective armature formula 1.2.1) and has probably originated from an ancestor similar to some modern day Megastygonitocrella species. Also, the nature of these armature elements is exactly the same in the two genera. Lee & Huys (2002) justified the erection of the genus Inermipes Lee & Huys, 2002 mostly by the following four characters: an antennal exopod armed with only one apical element, basis of all swimming legs lacking the outer armature element, a highly reduced fifth leg and an unusually large spermatophore in the male. The first character was also observed in Lucionitocrella yalleenensis gen. et sp. nov. (see above), although the two species have very little in common, but also in some other ameirids that are completely unrelated (see Karanovic, 2006). Swimming legs without the outer armature element on the basis can be found in both Psammonitocrella Huys, 2009 species (see below), although only on the first and second legs. As can be witnessed in the descriptions of new species in this paper, the fifth leg can be variously reduced and sometimes much more so than in Inermipes , but it was previously also known to be completely reduced in Stygonitocrella orghidani ( Petkovski, 1973) and Reidnitocrella djirgalanica ( Borutzky, 1978) comb. nov. (see Petkovski 1973; Borutzky 1978). However, the enormous spermatophore, occupying nearly half of the body of Inermipes humphreysi Lee & Huys, 2002 , is remarkable and it has not been reported so far in any other ameirid. Another autapomorphic feature of this genus is the enlarged first exopodal segment of all swimming legs. These two characters are sufficient to define Inermipes as a separate genus, but, being uninformative, were not included in the cladistic analysis of Stygonitocrella s. l. (see above).

The interestingly constricted habitus of I. humphreysi was also observed in one newly described species of the genus Megastygonitocrella gen. nov. (see below), but probably originated convergently in the two taxa. Reductions in the armature of the mouth appendages and antennula observed in Inermipes are also found in some other members of this group of freshwater ameirids and seem to be of limited phylogenetic importance, although many species have these characters only partly described or completely unknown. For example, a completely absent maxillular endopod was reported in I. humphreysi , Kimberleynitocrella billhumphreysi gen. et sp. nov., Psammonitocrella boultoni Rouch, 1992 and Stygonitocrella montana ( Noodt, 1965) , but this appendage is unknown in 11 species (see Table 2, characters 10 & 11 and also Noodt (1965), Rouch (1992) and Lee & Huys (2002)). A first antennular segment without any armature is found in, besides Inermipes , both species of the genus Psammonitocrella , as well as in Eduardonitocrella mexicana ( Suárez-Morales & Iliffe, 2005) comb. nov. It is one of the most important apomorphic characters (probably homoplastic!) that groups these dissimilar ameirids in the same clade (see the Discussion part of this paper), although they are probably not very closely related at all.

Two other problematic species on this branch are: Neonitocrella insularis ( Miura, 1962) and Stygonitocrella orghidani ( Petkovski, 1973) . The latter one is so poorly described that we include it as incertae sedis in the newly redefined genus Stygonitocrella Reid, Hunt & Stanley, 2003 (see above). Both species share with Inermipes a reduced armature on the third endopodal segment of the first leg ( Table 2, character 22), which probably is a homoplastic character as it was also found in Stygonitocrella guadalfensis Rouch, 1985 (see Miura 1962; Petkovski 1973; Rouch 1985).