Stygonitocrella Reid, Hunt & Stanley, 2003

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 : 35-37

Genus Stygonitocrella Reid, Hunt & Stanley, 2003

Diagnosis emended. Small to medium sized Ameiridae , with cylindrical habitus and no distinct demarcation between prosome and urosome. Integument weakly chitinized, with or without cuticular windows on prosomites; hyaline fringe of prosomites smooth, those of urosomites smooth or finely serrated. First pedigerous somite incorporated into cephalothorax. Prosome weakly ornamented with moderately large sensilla, urosome additionally ornamented with ventral posterior rows of small spinules. Genital somite free or fused with first abdominal in double-somite; genital field with single large copulatory pore, wide copulatory duct and two small semicircular seminal receptacles; single small genital aperture covered by fused reduced sixth legs. Anal operculum wide and convex, reaching to posterior end of anal somite, smooth or ornamented with small spinules near posterior margin. Caudal rami from one to five times as long as their greatest width and slightly divergent; armed with seven armature elements (three lateral, one dorsal and three apical), all positioned at posterior end. Antennula long and slender, eight-segmented in female and tensegmented and geniculate in male; with one seta on first segment. Antenna composed of coxa, basis, twosegmented endopod and one-segmented exopod; exopod armed with two or three setae. Mandibula with narrow cutting edge and two-segmented palp; basis armed with single seta, endopod with three to five apical setae. Maxillular endopod with one apical seta. Maxilla with two endites on syncoxa; endopod minute, armed with two slender setae. Maxilliped three-segmented, with or without seta on syncoxa and without seta on endopod. All swimming legs with three-segmented exopod. Endopod of first leg three-segmented; endopod of second and third swimming legs one- or two-segmented, while endopod of fourth swimming leg always onesegmented. All exopodal segments of about same length; first exopodal segment of all legs without inner seta, second with; third exopodal segment of all swimming legs with two outer spines, that of first leg without inner setae, second and third leg without inner setae (except for S. orghidani Petkovski, 1973 ) and fourth leg with one or two inner setae. First endopodal segment of first leg large, at least as long as first two exopodal segments combined, with or without inner seta; apical endopodal segment of second, third and fourth legs armed with long apical seta. Basis of first leg in male with transformed inner spine; no other sexual dimorphism in swimming legs. Fifth legs similar in both sexes, variously reduced but always distinct from somite, with three elements on baseoendopod and maximum of four on exopod. Sixth legs in male armed with two setae maximum.

Type species. Stygonitocrella montana ( Noodt, 1965) [= Nitocrella montana Noodt, 1965 ].

Other species. Stygonitocrella dubia ( Chappuis, 1937) [= Nitocrella dubia Chappuis, 1937 ]; Stygonitocrela guadalfensis Rouch, 1985 ; and Stygonitocrella sequoyahi Reid, Hunt & Stanley, 2003 .

Incertae sedis. Stygonitocrella orghidani ( Petkovski, 1973) [= Nitocrella orghidani Petkovski, 1973 ].

Synonymy. Fiersiella Huys, 2009 .

Remarks. As mentioned in the Introduction section, while describing this genus Petkovski (1976) did not designate a type species, which according to the ICZN (Article 13.3) means that this name was unavailable. In order to be available every new genus-group name published after 1930 must be accompanied by the fixation of a type species, in addition to satisfying the provisions of Article 13.1, i.e. providing or citing a description or definition of the genus. Reid et al. (2003) designated the South American Stygonitocrella montana ( Noodt, 1965) as the type species of the genus Stygonitocrella Reid, Hunt & Stanley, 2003 and gave a revised diagnosis, making the generic name available with their authorship. This was accepted by Lee & Huys (2002), Karanovic (2006) and Wells (2007), although Suárez-Morales & Iliffe (2005) continued to attribute authorship to Petkovski (1976). Unfortunately, Reid et al. (2003) also treated all previously described species as new combinations and cited all author names in parentheses. Although, neither Article 11.9.3 nor Article 51.3 specifically addresses this case, it remains unclear as to whether the name of the author of a species that was assigned originally to an unavailable genus is designated in parentheses, after the same genus name has become available under different authorship. This is not a case of a generic name being different from the original one, since the author attribution does not form part of a name in zoological nomenclature (Article 51.1). Therefore, we think parentheses should not be used and it is at least an overstatement to refer to such cases as new combinations.

Suárez-Morales & Iliffe (2005) also proposed the subdivision of Stygonitocrella into two subgenera, Eustygonitocrella Suárez-Morales & Iliffe, 2005 and Fiersiella Suárez-Morales & Iliffe, 2005 , based on the condition of the female fifth leg baseoendopod. As we can see in the cladisitic analysis in this paper, characters of the fifth leg have very little importance at the generic (or subgeneric level), as they can be very different in some obviously closely related species ( Megastygonitocrella pagusregalis sp. nov. and Megastygonitocrella kryptos sp. nov. for example—see below), but can also be superficially similar in different genera (see the Remarks section for Lucionitocrella yalleenensis gen. et sp. nov.). We think their subdivision of the genus is not taxonomically sound and by definition excludes those species that are known just as males, although Suárez-Morales & Iliffe (2005) included Stygonitocrella dubia ( Chappuis, 1937) , for which females are still unknown. Also, their revision suffers from some serious nomenclatural problems. As Wells (2007) pointed out, Eustygonitocrella is obviously an objective synonym of Stygonitocrella , since it contains the type species S. montana , and must, therefore, be relegated to a junior synonym of the nominotypical subgenus (ICZN Article 44.1). For the subgenus Fiersiella , the authors designated S. dubia as “... the representative species ...”, without following the rules of the ICZN (Article 67.5), making this genusgroup name unavailable. According to the provisions of the Code, type designation must be rigidly constructed by using the term “ type species” (or an equivalent term in another language) to avoid ambiguity. Huys (2009) made the subgeneric name available by fixing Stygonitocrella sequoyahi Reid, Hunt & Stanley, 2003 as the type species. Unfortunately, as our cladistic analysis shows, both S. dubia and S. sequoyahi belong to the same clade as the type species of Stygonitocrella , and consequently, Fiersiella Huys, 2009 is considered here as a subjective junior synonym of the former.

The genus Stygonitocrella , as redefined here, contains only four species: S. montana from Argentina, S. sequoyahi from the United States of America and S. dubia and S. guadalfensis Rouch, 1985 from Spain (see Chappuis 1937; Noodt 1965; Rouch 1985; Reid et al. 2003). Reid et al. (2003) pointed out that the generic placement of Stygonitocrella orghidani ( Petkovski, 1973) is questionable and Lee & Huys (2002) formally placed it as incertae sedis in the wider defined genus Stygonitocrella . As noted both by Lee & Huys (2002) and Reid et al. (2003), the description of this Cuban species by Petkovski (1973) is not sufficient for modern taxonomic standards and we also include it here in the redefined genus Stygonitocrella as incertae sedis solely on the basis of the endopodal armature of the swimming legs, although it does not cluster with this group of freshwater ameirids. Unfortunately, the type material of this species no longer exists (T. Petkovski pers. comm.) and any further taxonomic decision would have to await study of newly collected topotypes.

The main character that defines Stygonitocrella is the armature formula of the ultimate endopodal segment of the second to fourth swimming legs, which is 1.1.1 and is not found in any other group studied here. The five taxa included herein in this genus are united by the loss of the outer subapical spine of the third leg endopod ( Table 2, character 35). This feature is convergently exhibited in three other genera: Gordanitocrella gen. nov., Lucionitocrella gen. nov. and Psammonitocrella Huys, 2009 . The first two genera are discussed above and are not closely related to Stygonitocrella , as they each have a greater number of plesiomorphic characters in their swimming legs, but more reduced mouth appendages and antenna. The genus Psammonitocrella is very well defined by a number of autapomorphic features, such as its unusually reduced exopodal armature of the swimming legs and the absence of a transformed inner basal spine of the male first leg, as well as some other unusual reductions (see below). However, it is not so hard to imagine the ancestor of Psammonitocrella being morphologically quite similar to S. sequoyahi , and it is interesting to note that both species of Psammonitocrella and S. sequoyahi live in North America and have unusually elongated caudal rami.

The only armature element on the ultimate endopodal segment of the second leg in Stygonitocrella is probably the ancestral inner apical seta (just as in the third leg), but this is not so easy to confirm with less than perfect drawings of some members of the genus. The nature of the only armature element on the fourth leg endopod is also not so clear, but we believe it to be the ancestral outer subapical spine, as in the genus Megastygonitocrella gen. nov. (see below). The mouth appendages are described only for two species in this genus ( S. sequoyahi and S. guadalfensis ), but interestingly both have some unusual plesiomorphic characters, like the presence of a mandibular basal seta (only present in one other species studied here, i.e. M. karamani ( Petkovski, 1959)) and two endites on the maxillar syncoxa (also reported for S. montana ). Unfortunately, many earlier species descriptions in this group of freshwater ameirids lack some or most data on mouth appendages (see Table 2).