Ambiaxius Sakai

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 : 8

Genus Ambiaxius Sakai & de Saint Laurent, 1989

Remarks. Ambiaxius was originally established by Sakai & de Saint Laurent (1989) to accommodate two species, Calocaris alcocki McArdle, 1900 and Calocaris aberrans Bouvier, 1905 . Kensley (1989) also described a new genus Callistocaris for Calocaris alcocki , but his paper was published two months later than Sakai & de Saint Laurent’s work. Thus Callistocaris is a junior objective synonym of Ambiaxius . Since then, four new species have been described in this genus, A. franklinae Sakai, 1994 from Australia, A. japonicus Kensley, 1996 from Japan, A. foveolatus Kensley, Lin & Yu, 2000 from Taiwan, and A. surugaensis Sakai & Ohta, 2005 from Japan. Sakai & Ohta (2005) proposed a new genus, Briancaris , for A. aberrans , A. japonicus (type species) and A. foveolatus . Sakai & Ohta (2005) argued that Briancaris differs from Ambiaxius in the short, triangular rostrum with denticulate lateral margins and the structure of the second pleopod. In Ambiaxius , the rostrum is slender and upturned, bearing one or two tiny lateral spines. With regard to the second pleopod, they noted that “distal segment of endopod enlarged with a boot-shaped appendix masculina with a small protrusion, on which is a small appendix interna, that is slightly distant from basal segment” for Ambiaxius , while that “distal segment of the endopod enlarged with a small appendix interna, which is attached close to the proximal segment basally” for Briancaris . However, these conditions are barely distinguishable. Except for the shape of the rostrum, the diagnostic features of Ambiaxius and Briancaris are virtually identical, and thus the status of Briancaris is questionable. Sakai & Ohta (2005) gave the confusing comment that “Kensley’s Callistocaris is obviously different from Sakai & de Saint Laurent’s (1989) Ambiaxius ”, even though these two genera were based on the same type species (i.e., Calocaris alcocki ). We prefer to synonymize Briancaris with Ambiaxius .