Ambiaxius 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 : 237-238

Ambiaxius Sakai and de Saint Laurent, 1989

Ambiaxius Sakai and de Saint Laurent, 1989: 54 .— Poore, 1994: 99 (key).— Sakai and Ohta, 2005: 82.

Callistocaris Kensley, 1989: 961 (objective synonym: same type species).

Diagnosis. Carapace smooth; cervical groove visible laterally over most of distance to anterolateral margin. Rostrum triangular or spine-like, dentate or not, longer than eyestalks, depressed below level of carapace, continuous with lateral carinae; supraocular spines prominent; lateral carina weak; submedian carina absent; median carina smooth; postcervical carina absent. Abdominal somite 1 pleuron triangular; pleuron 2 posteriorly rectangular; pleura 3–5 posteriorly rounded.Eyestalk cylindrical, articulating; cornea unpigmented. Antenna, scaphocerite short. Maxilliped 3 exopod not clearly bent at base of flagellum. Pleurobranchs absent above pereopods 2–4; podobranchs and arthrobranchs present; epipods present on maxilliped 2 to pereopod 4. Pereopods 1 asymmetrical, with propodus cylindrical; propodus with spine on upper margin. Pereopods 3–5 propodi with transverse rows of robust setae; dactyli 3 and 4 elongate, with scattered robust setae; dactylus 5 elongate. Pleopods 3–5, appendix interna present. Hermaphroditic. Pleopod 1 article 1 flattened; article 2 subtriangular, one-third length of first, folded obliquely, posterior part distally lobed, anterior part smaller, narrower, with distal margin oblique, with short appendix interna. Pleopod 2 endopod article 2 elongate-triangular, as long as article 1, mesial margin concave, with basal thumb-like appendix interna, appendix masculina with a row of strong spines followed by a short apical setose appendage. Uropodal exopod with transverse suture. Telson without lateral teeth, without posterolateral robust setae; apex deeply rounded and continuous with lateral margins.

Remarks. Species of Ambiaxius are recognised by the prominent supraocular spines, unarmed and obsolete or absent gastric carina, being hermaphroditic, triangular short second article on pleopod 1, and pleopod 2 endopod elongate-triangular, with concave mesial margin and short setose end. The genus is closest to Calastacus Faxon, 1893 (see below). Sakai and Ohta (2005) distinguished their new genus Briancaris from Ambiaxius on the shape of the rostrum, the former having a broad triangular toothed rostrum while the latter has a styliform rostrum that is barely toothed if at all. These differences are slight and otherwise the two genera, each of three species, have virtually identical pleopods.

Ambiaxius franklinae , from the Coral Sea, is the only Australian species known so far. A specimen of another species, too incomplete to describe, is recorded below.