Formosaxius, Lin, Tomoyuki Komai Feng-Jiau & Chan, Tin-Yam, 2010

Lin, Tomoyuki Komai Feng-Jiau & Chan, Tin-Yam, 2010, Five new species of Axiidae (Crustacea: Decapoda: Axiidea) from deep-water off Taiwan, with description of a new genus, Zootaxa 2352, pp. 1-28 : 2-3

Formosaxius n. gen.

Type species: Formosaxius dorsum n. sp. Gender: masculine.

Diagnosis. Rostrum triangular, acute, laterally spinose, longer than eyestalks, not much depressed below level of carapace, continuous with distinct lateral carinae on gastric region of carapace. Carapace smooth; dorsal surface strongly convex, anterior part sloping down to rostrum; cervical groove visible laterally over almost half distance to anterolateral margin; supraocular spines barely differentiated from other spines; lateral carina smooth; submedian carina present, consisting of row of spines; median carina with few spines anteriorly; postcervical carina present at least in posterior half. First abdominal pleuron rounded ventrally; second pleuron broad, rounded; third to fifth pleura posteriorly rounded. Telson with 2 minute, marginal spiniform setae at each posterolateral angle; posterior margin rounded, unarmed medially. Eyestalk cylindrical, articulating; cornea pigmented. Antenna with scaphocerite long, acute. Third maxilliped with exopod not clearly bent at base of flagellum. Gill formula summarized in Table 1; pleurobranchs present on fifth to seventh thoracic somites (above bases of second to fourth pereopods); podobranchs and arthrobranchs well developed; epipods present on second maxilliped through fourth pereopod. First pereopod (only one side known at present) with laterally compressed palm; dorsal margin of carpus to dactylus smooth, with subdistal tooth on palm; cutting edges of fingers each with row of corneous spinules. Third to fifth pereopods with propodi lacking transverse rows of spiniform setae; dactyli of third and fourth pereopods subconical, slender, slightly twisted, only that of fourth pereopod with spiniform setae. Fourth pereopod with well-developed grooming apparatus on propodus. Third to fifth pleopods each with well-developed appendix interna. Uropodal exopod with transverse suture.

Thoracic somites

1 2 3 4 5 6 7 8

Maxillipeds Pereopods

1 2 3 1 2 3 4 5 Pleurobranchs 0 0 0 0 1 1 1 0 Arthrobranchs 0 1 2 2 2 2 2 0 Podobranchs 0 0 r r r r r 0 Epipods 1 1 1 1 1 1 1 0 Exopods 1 1 1 0 0 0 0 0 Remarks. At present 23 genera are known in Axiidae ( Poore 1994; Sakai 1994; Kensley 1996b; Sakai & Ohta 2005; Komai & Tachikawa 2007, 2008; Clark et al. 2007; De Grave et al. 2009). Only female specimens of F. dorsum are presently known, so no information on male pleopods is available. Nevertheless, the presence of pleurobranchs, the general armature of the rostrum and the arrangement of the carapace gastric carinae, the simple antennal scaphocerite, and the lack of spines on the dorsal margins of the cheliped palms link Formosaxius to Bouvieraxius Sakai & de Saint Laurent, 1989. In these two genera, the lateral margin of the rostrum is spinose, but the supraocular spine is not differentiated; the submedian gastric carina consists of a row of spines; and the lateral gastric carina is unarmed. However, the possession of appendices internae on the third to fifth pleopods immediately distinguishes the new genus from Bouvieraxius . Furthermore, the ventrally rounded first pleuron seems to differentiate the new genus from Bouvieraxius . The fingers of the cheliped (only one side is known) are armed with a row of corneous spinules on the cutting edges, a character not known at present for other axiid species. This character may be of generic significance. Planaxius Komai & Tachikawa, 2008 is also similar to Formosaxius n. gen. in having pleurobranchs and appendices internae on the third to fifth pleopods. However, Planaxius differs from the new genus in the lack of gastric submedian carinae on the carapace. The unarmed median gastric carina and the possession of spinules on the lateral faces of the dactyli of the third to fifth pereopods are also major characters separating Planaxius from Formosaxius n. gen. In the new genus, the median gastric carina is armed with two spines and one obtuse tubercle; the dactyli of the third and fifth pereopods are devoid of spinules on the lateral faces.

Etymology. The name is derived from the combination of Formosa (old name of Taiwan) and the generic name Axius , in reference to the type locality of the new species.