Heteronika, Hendrickx, 2019

Hendrickx, M. E., 2019, Redescription of the rare shrimp Heterocarpus nesisi (Burukovsky, 1986) (Crustacea: Caridea: Pandalidae) rediscovered off western Mexico, with the proposal of a new genus, Zootaxa 4565 (1), pp. 49-60 : 50

Heteronika gen. nov.

Diagnosis. Rostrum not movable, fixed to carapace. Dorsal and ventral teeth present, subtriangular, large, well separated. No movable spines on prolongation of rostrum on carapace. Carapace with one well marked lateral keel arising from above the antennal spine and extending to at least 2/3 of the carapace length. Carapace dorsally carinated anteriorly, rounded posteriorly. No supraorbital spine. Abdominal somites without dorsal keel, without posterior spine. Cornea wider than eyestalk. Maxilliped 2 terminal segment wider than long. Third maxilliped with exopod. Second pair of pereiopods strongly dissimilar, one stouter and shorter than the other, carpus subdivided in 17–18 segments (left) and (at least) 5 segments (right). No tegumental scales.

Remarks. The original description of Heterocarpus nesisi (see Appendix) was based on a single male (holotype) of 76 mm (measured from the base or rostrum to the end of telson) captured in 1975 on a seamount located off the northeast coast of America ( Burukovsky 1986). It was later transferred to Plesionika (see Chan & Crosnier 1997). Generic definition within the Pandalidae is rather unclear. It seems obvious that both Plesionika and Heterocarpu s contain several species with morphological characters that do not fit with one another, making both genera heterogeneous. Because it possesses one strong lateral keel " Heterocarpus nesisi " cannot be readily classified within the genus Heterocarpus or within the genus Plesionika . Diagnosis provided by Chace (1989: 19, 43) and by Holthuis (1993: key to genera) for Heterocarpus and Plesionika are very similar, and basic differences are restricted to ( Heterocarpus vs. Plesionika ): the postrostral dorsal carina reaching to nearly posterior margin vs. the postrostral part of the carapace rounded; the presence (1 or 2) vs. absence of lateral keels on carapace; the carpus of second pair of pereopods divided into 7–12 (left) and 18–25 (right) articles vs. divided into more than 3 articles. Plesionika third somite is also unarmed or features a fixed posteromesial spine, while in Heterocarpus several somites are armed with a posteromesial spine (see Table 1).

Chace (1989: 88) suggested that H. laevis A. Milne-Edwards, 1883 and H. alexandri A. Milne-Edwards, 1883 "might eventually constitute a separate genus". While referring to Chace (1989) suggestion, Chan & Crosnier (1997: 204) emphasized the fact that "the increasing number of species belonging to the " P. laevis " group may prompt some workers to follow Chace's (1989) suggestion and propose a separate genus for them". In the case of nesisi it seems impossible to keep this species within the genus Heterocarpus mostly because of the absence of a second, well marked lateral keel. Its affinity with Plesionika is rather obscure and is difficult to asses because of the complexity of this genus and the great variety of forms it contains, but differences seem sufficient to consider that he cannot remains in Plesionika either (see Table 1).

Ethymology and type species. The new generic name denote the intermediate position of Heteronika between Heterocarpus (Hetero-) and Plesionika (-nika), united to form the name Heteronika . Type species: Heterocarpus nesisi Burukovsky, 1986 , by original designation.

Other species included. The material reported by Chan & Crosnier (1997) as " Plesionika nesisi " probably belongs to a different species and should be included in Heteronika gen. nov. once this is confirmed. Heterocarpus alexandri A. Milne-Edwards, 1883 , fits well with the diagnosis of Heteronika gen. nov. and it is herein proposed as a new combination, Heteronika alexandri new comb. The presence of a sharply defined middorsal boss on third somite in H. alexandri ( Chace 1989: 85) and in the material identified as " Plesionika nesisi " by Chan & Crosnier (1997) matches a similar but weakly defined boss in Heteronika nesisi . Species of Heterocarpus and Plesionika need to be reviewed in details and once this is achieved it will most probably lead to splitting these heterogeneous groups of species into several genera. As a consequence, some additional species with a single lateral carina on the carapace might then be included in Heteronika gen. nov.