Eduardonitocrella, Karanovic & Hancock, 2009

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 : 44-45

Genus Eduardonitocrella gen. nov.

Diagnosis. Medium sized Ameiridae , with robust and almost fusiform habitus but without distinct demarcation between prosome and urosome. Integument relatively strongly chitinized and without cuticular windows; hyaline fringe of all prosomites smooth, those of urosomites finely serrated. First pedigerous somite incorporated into cephalothorax. Prosome ornamented with sensilla and small pits only, urosome additionally ornamented with rows of small spinules. Genital somite free; genital field unknown. Anal operculum narrow and very short, reaching only to midlength of anal somite, ornamented with many small spinules near posterior margin. Caudal rami conical, as long as greatest width and slightly divergent; dorsal seta inserted close to inner margin, shorter than ramus; proximal lateral seta arising somewhat dorsolaterally at 2/3 and distal lateral seta arising posterolaterally, both very short; inner apical seta as long as ramus; principal apical setae with breaking plane. Antennula long and slender, eight-segmented in female (male unknown), without distal seta on first segment, but with proximal sensillum instead. Antenna composed of coxa, basis, twosegmented endopod and one-segmented exopod; exopod armed with two setae. Labrum with very narrow cutting edge. Mandibula with narrow and pointed cutting edge and two-segmented small palp; basis unarmed, endopod with two apical setae. Maxillular endopod armed with single apical seta. Maxilla with single endite on syncoxa; endopod armed with single apical seta. Maxilliped three-segmented, unarmed. All swimming legs with three-segmented exopod. Endopod of first leg three-segmented; endopod of other legs onesegmented and about as long as first exopodal segment. All exopodal segments of about same length; first exopodal segment of all legs and second exopodal segment of first leg without inner seta; second exopodal segment of other legs with inner seta; third exopodal segment of first leg with three outer spines and no inner setae, that of other legs with two outer spines and without inner setae. First endopodal segment of first leg unarmed, long and slender, almost reaching to posterior margin of second exopodal segment; endopod of second leg with two slender apical setae, that of third and fourth legs with one inner and two apical setae. Fifth leg almost completely fused to somite, represented by two lateral knobs; inner knob, representing exopod, armed with two smooth slender setae; outer knob represents outer part of basis and armed with single seta; endopodal lobe absent.

Type and only species. Eduardonitocrella mexicana ( Suárez-Morales & Iliffe, 2005) comb. nov. [= Stygonitocrella (Eustygonitocrella) mexicana Suárez-Morales & Iliffe, 2005 ].

Etymology. The genus is named in honour of Dr Eduardo Suárez-Morales (ECOSUR, Mexico), who described the type species. His first name is prefixed to the existing genus name Nitocrella . Gender feminine.

Remarks. A combination of plesiomorphic and apomorphic characters clearly define this genus. Its endopodal armature formula of second to fourth swimming legs (2.3.3) is unique in this group of freshwater ameirids, as is its very short anal operculum, which so far has been recorded only in marine and anchialine representatives of this family (the outgroup in our cladistic analysis being one of them; see above). Besides the outgroup, Eduardonitocrella mexicana ( Suárez-Morales & Iliffe, 2005) comb. nov. is unique among the species examined in this study by the presence of an inner apical seta on the ultimate endopodal segment of the second leg ( Table 2; character 27) and shares characters 37 and 46 only with Lucionitocrella yalleenensis gen. et sp. nov.

We have explained the different nature of the three armature elements on the third leg endopod in the Remarks section for the genus Gordanitocrella gen. nov., as well as some major differences in the endopodal armature of the second and fourth legs between Eduardonitocrella and Lucionitocrella in the Remarks section for the latter genus. Most of these characters are plesiomorphic, as is the armature of the third exopodal segment of the first leg (character 19), which Eduardonitocrella shares only with Gordanitocrella and Kimberleynitocrella gen. nov. However, unlike these monospecific Australian genera, Eduardonitocrella has lost the inner seta on the first endopodal and second exopodal segments of the first leg (characters 17 & 20), as well as a number of reductions in the antennula, antenna and the mouth appendages. None of the latter reductions is unique. For example, a first antennular segment without armature (character 6) has been reported also in Psammonitocrella Huys, 2009 and Inermipes Lee & Huys, 2002 , while a reduced armature on the mandibular endopod is recorded in Psammonitocrella and Neonitocrella Lee & Huys, 2002 (see Miura 1962; Rouch 1992; Lee & Huys 2002). Suárez-Morales & Iliffe (2005) erroneously reported a small proximal sensillum on the first antennular segment as a “short seta”, but the real nature of this ornamentation (not armature) element is most probably a chemoreceptor. A very similar sensillum was observed on the male antennula of the below described Megastygonitocrella ecowisei gen. et sp. nov. which is probably homologous to the tubular pore in Parapseudoleptomesochra tureei Karanovic, 2006 , the ordinary cuticular pore in Abnitocrella eberhardi Karanovic, 2006 or the “setule” in Nitocrella trajani Karanovic, 2004 (see Karanovic 2004a, 2006).

Eduardonitocrella differs also from other members of Stygonitocrella s. l. by its relatively robust habitus (with almost fusiform prosome), but the only autapomorphic features seem to be its extremely elongated and narrow labrum, as well as a very large mandibular coxa, which makes the mandibular palp look relatively very small. The fifth leg is also quite reduced in this genus, but we have discussed above the limited value of this character at the generic level.