Paragathotanais Lang, 1971

Larsen, Kim, 2007, Family Agathotanaidae Lang, 1971 a *, Zootaxa 1599, pp. 41-60 : 48-49

Genus Paragathotanais Lang, 1971 b

Type species. Paragathotanais typicus Lang, 1971 b

Generic remarks. This genus was erected by Lang (1971b) to accommodate his new species P. t y p i c u s (by monotypy) from the Vema Expedition in the Caribbean Sea. Paragathotanais is also a cosmopolitan genus to be found in any deep-water sampling around the world ( Kudinova-Pasternak 1970; Bird & Holdich 1988; Larsen 2002). The most recent key to the genus is given by Larsen (2005) but the addition of new taxa requires a modification of that key.

Although there are no problems in separating Agathotanais and Paragathotanais there seem to be some difficulties in separating the genera Paragathotanais from Paranarthrura , although the characters given by Lang (1971a) appear to be fairly easy at first glance. The diagnostic characters for Paragathotanais separating it from Paranarthrura , are (as stated by Lang): “labium as in Agathotanais ; cheliped without pseudocoxa; uropod without exopod process”. However, as quite often within Tanaidacean systematics, things are not quite as simple as expected. The labium of Paragathotanais does indeed have a setulate medial seta or projection, but is hardly ‘as in Agathotanais’ as it is lacking the prominent process on the outer lateral corners found in the labium of Agathotanais ( Bird & Holdich 1988; Larsen 2002, 2005). Regarding the uropod exopodal process, this is much more obvious and often acute in Paranarthrura but still, such a structure is visible in certain species of Paragathotanais ( Bird & Holdich 1988; Gurreo-Kommritz 2003) albeit very reduced. As for the cheliped pseudocoxa the situation is not quite clear cut either. Larsen (2002) described P. medius as having a pseudocoxa, although later he (2005) withdrew that character, stating that this was the result of a bad dissection. It is now clear that the Paragathotanais cheliped is attached to the carapace via a large sclerite (which often comes off with the cheliped during dissection). Also Bird & Holdich (1989) noted and illustrated the differences in the degree of fusion/no fusion of ‘sclerite/pseudocoxa’ within the Paranarthrura and suggested potential taxonomic value. This sclerite has also been suggested homologous with the pseudocoxa by Larsen & Wilson (2002) and this is supported by the observations conducted in this study. Although the cheliped sclerite of Paragathotanais can be morphologically separated from the pseudocoxa of Paranarthrura , some species of Paranarthrura does not posses a pseudocoxa but rather a sclerite. Thus we are left without any clear-cut differentiating characters between Paragathotanais and Paranarthrura and these genera must be seen as gradual evolutionary line, in the direction from Paranarthrura via Paragathotanais to Agathotanais . It is here suggested that the best way to separate Paranarthrura from Paragathotanais , is by the larger and more lateral attachment of the uropods in Paranarthrura . For identification it is recommended to view the animal habitus from the dorsal view; if the uropods protrude latero-distally from the pleotelson, the species can be referred to Paranarthrura , it they are not visible then to Paragathotanais .

Kudinova-Pasternak (1970) described Paranarthrura zevinae from the Kurile-Kamchatka Trench (before the genus Paragathotanais was established), although her species does not display any uropod exopodal process. She did not illustrate the labium but did ( Kudinova-Pasternak 1970:368, plate19) illustrate a structure which could be either a sclereite or a psedodocoxa. Given the considerations raised above, Paranarthrura zevinae should be placed in Paragathotanais rather than in Paranarthrura owing to the small ventrally-attached uropods.