Neonitocrella 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 : 43-44

Genus Neonitocrella Lee & Huys, 2002

Diagnosis emended. Medium sized Ameiridae , with cylindrical habitus and no distinct demarcation between prosome and urosome. Integument weakly chitinized and without cuticular windows; hyaline fringe of all somites smooth. First pedigerous somite incorporated into cephalothorax. Prosome only ornamented with sensilla, urosome additionally ornamented with short posterior ventral rows of small spinules. Genital somite free; genital field with single large copulatory pore, wide and short copulatory duct and two small semicircular seminal receptacles; single small genital aperture covered by fused reduced sixth legs. Anal operculum wide and convex, not reaching to posterior end of anal somite, ornamented with many minute 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 close to posterior lateral margin; inner apical seta as long as ramus; principal apical setae with breaking plane. Antennula long and slender, eight-segmented in female and ten-segmented in male; with seta on first segment. Antenna composed of coxa, basis, two-segmented endopod and one-segmented exopod; exopod armed with two setae. Mandibula with narrow cutting edge and two-segmented palp; basis unarmed, endopod with five apical setae. Maxilla with single endite on syncoxa. Maxilliped three-segmented, prehensile. All swimming legs with threesegmented exopod. Endopod of first leg three-segmented; endopod of second and third swimming legs onesegmented, while that of fourth swimming leg reduced to a small knob. All exopodal segments of about same length; first exopodal segment of all legs, as well as second segment of first leg, without inner seta; second exopodal segment of second, third and fourth legs with inner seta; third exopodal segment of all legs with two outer spines and that of first, second and third legs without inner setae, but that of fourth leg with one inner seta. First endopodal segment of first leg large, almost reaching to posterior margin of second exopodal segment, armed with short spiniform inner seta; endopod of second and third legs slightly shorter than first exopodal segment, armed with inner apical plumose seta and much shorter outer apical spine. Basis of first leg in male probably with transformed inner spine; 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 two apical setae in female and with additional inner seta in male.

Type and only species. Neonitocrella insularis ( Miura, 1962) [= Nitocrella insularis Miura, 1962 ].

Remarks. This genus was erected to accommodate a single Japanese species, Nitocrella insularis Miura, 1962 , so far known only from the Ryukyu archipelago ( Miura 1962). Lee & Huys (2002) pointed out its reduced endopod of the fourth leg, a bisetose antennal exopod and reduced fifth legs as the main distinguishing characters. As we have seen so far, the value of the last character is very limited and a very similar fifth leg was reported by Sterba (1973) for Reidnitocrella pseudotianschanica ( Sterba, 1973) comb. nov. Similarly, a bisetose antennal exopod has been observed in a number of freshwater ameirids, including two unrelated species described in this paper. A completely absent endopod of the fourth swimming leg or its presence just as a small knob, is seen also in Kimberleynitocrella billhumphreysi gen. et sp. nov. (see above) and in both species of the genus Psammonitocrella Huys, 2009 (see Rouch 1992). This reduction apparently originated independently in these three lineages, as they have hardly anything else in common.

Miura (1962) listed a total of five males, but makes no comment on their variability or bilateral asymmetry. He illustrated only the right fifth leg and it is interesting to note its similarity with the condition in Gordanitocrella gen. nov. and Inermipes Lee & Huys, 2002 , but in the description he only stated: “Exopodite of P5 different in shape from that of female and bears 3 setae”. We would not be surprised if a closer examination of this and some additional material shows this character to be asymmetric. Lee & Huys (2002) in their diagnosis of the genus Neonitocrella Lee & Huys, 2002 mistakenly state that there is sexual dimorphism in “P3 endopod, ..., and in genital segmentation”, but it is clear from the original drawings that the genital and first abdominal somites are separate in the female and Miura (1962) specifically states that in the male “endopodite of P3 not modified”.

As we have explained in the Remarks section for the genus Inermipes Lee & Huys, 2002 , Neonitocrella shares with Psammonitocrella a reduced armature of the third endopodal segment of the first leg, but this character is homoplastic and Psammonitocrella is a genus very well defined by a number of autapomorphic characters. Neonitocrella probably originated from some primitive Megastygonitocrella -like ancestor, as the armature of the endopodal segment of the second and third legs is the same as in M. karamani ( Petkovski, 1959) comb. nov., although the latter species has a two-segmented endopod on these legs (one-segmented in N. insularis ) and a one-segmented endopod of the fourth leg armed with a single apical spine. An endopod that is reduced to a small knob is technically still present, so we decided to use armature elements instead in the matrix presented above ( Table 2). It is interesting to note that there is no normally developed apical endopodal segment without any armature elements in ameirids, which probably means that the reduction in the segment size and the loss of its last armature element occurred concurrently in a single event.

The genus Neonitocrella can be distinguished from all other ameirids by its unique armature formula of the ultimate endopodal segment of the second to fourth swimming legs, which is 2.2.0.