Acanthaxius Sakai and de Saint Laurent, 1989

Poore, Gary C. B. & Collins, David J., 2009, Australian Axiidae (Crustacea: Decapoda: Axiidea), Memoirs of Museum Victoria 66 (2), pp. 221-287 : 224

Acanthaxius Sakai and de Saint Laurent, 1989

Acanthaxius Sakai and de Saint Laurent, 1989: 66 (diagnosis, list of species).— Kensley, 1996d: 70–71 (diagnosis, list of species).

Type species. Axiopsis (Axiopsis) pilocheira Sakai, 1987 by original designation.

Diagnosis. Carapace generally smooth or spinose; cervical groove visible laterally over half distance to anterolateral margin. Rostrum spine-like, narrow, laterally obscurely denticulate, about as long as eyestalks, not depressed below level of carapace, continuous with definite lateral carinae; supraocular spines prominent (or not); lateral carina spinose; submedian carina present, spinose; median carina a spinose ridge; postcervical carina absent. Abdominal somite 1 pleuron acute; pleuron 2 broad, anteriorly rounded, posteriorly rounded; pleura 3–5 posteriorly rounded. Eyestalk cylindrical, articulating; cornea pigmented. Antenna, scaphocerite short, curved; distal spine on antenna article 2 anteromesially angled and acute. Maxilliped 3 exopod not clearly bent at base of flagellum. Pleurobranchs absent; podobranchs and arthrobranchs well developed; epipods present on maxilliped 2 to pereopod 4. Pereopods 1 asymmetrical, with propodus cylindrical; carpus-dactylus upper margins prominently spinose (or not). Pereopods 3–5 propodi with transverse rows of robust setae; dactyli tapering, with longitudinal row of robust setae. Pleopods 3–5, appendix interna present. Pleopod 1 of male absent (or present). Pleopod 2 of male with appendix masculina. Uropodal exopod with transverse suture. Telson with lateral fixed spines and posterolateral robust setae; apex truncate-rounded.

Remarks. Acanthaxius is a genus of 13 nominal species, from the Pacific Ocean and Caribbean Sea. Kensley (1996d) stated that “the definition of this genus contains some uncertainties” and was supported in this by Ngoc-Ho (2006). Most of its members are unambiguously recognised by the combination of spinose rostrum, supraocular spine, spine-bearing median, submedian and lateral gastric carinae on the gastric region of the carapace, narrow chelipeds (pereopods 1) with prominently spinose upper margin and elongate fingers, absence of pleurobranchs, absence of the male pleopod 1, and anteromesially angled acute distal spine on antenna article 2.

Some species, including the type species, are known only from females and the absence of the male pleopod 1 would appear to have been assumed by the authors of the genus from the condition in A. miyazakiensis Yokoya, 1933 that they redescribed from abundant material. The male pleopod 1 is absent also in species described subsequently, A. formosa Kensley and Chan, 1998 , A. grandis Kensley and Chan, 1998 , A. gadaletae Ngoc-Ho, 2006, A. clevai Ngoc-Ho, 2006 and one of the new species described here.

Two species, Calocaris (Calastacus) hirsutimana Boesch and Smalley, 1972 and Axiopsis (Axiopsis) caespitosa Squires, 1979 , both referred to Acanthaxius by Sakai and de Saint Laurent (1989), and A. polychaetes Sakai, 1994 do possess a male pleopod 1 and also differ from typical Acanthaxius in absence of a prominent supraocular spine, more compact propodus on the major cheliped with few lateral spines, and a prominent lateral spine on the telson. Acanthaxius spinulicauda ( Rathbun, 1902) is also less spinose than the type species. These species may well deserve another genus whose exceptions are given in parentheses in the diagnosis above.