Acanthaxius Sakai

Ngoc-Ho, Nguyen, 2006, Three species of Acanthaxius Sakai & de Saint Laurent, 1989, including two new to science, from the Solomon Islands and New Caledonia (Crustacea, Thalassinidea, Axiidae), Zootaxa 1240, pp. 57-68 : 58-59

Genus Acanthaxius Sakai & de Saint Laurent, 1989

Remarks

The genus Acanthaxius was created by Sakai & de Saint Laurent (1989) for eight species with Axiopsis (Axiopsis) pilocheira Sakai, 1987 as type species. Later, Sakai (1994) increased, with A. polycheates , the number of species to nine. Kensley (1996) considered that “ the definition of this genus contains some uncertainties ”, redefined it and limited the number of species to five: A. miyazakiensis (Yokoya, 1933) from Japan, A. amakusana (Miyake & Sakai, 1967) and A. polyacantha (Miyake & Sakai, 1967) from the East China Sea, A. pilocheira ( Sakai, 1987) from Japan, A. polychaetes Sakai, 1994 from the Great Barrier Reef, Australia, and added A. kirmilleri Kensley, 1996 from off Anguilla. Two other species were established in 1998: A. formosa Kensley & Chan and A. grandis Kensley & Chan , both from Taiwan.

Ngoc­Ho (2005), describing a specimen of Axius spinosissimus Rathbun, 1906 from French Polynesia, agreed with Kensley (1996) that although this species was placed in Acanthaxius by Sakai & de Saint Laurent (1989), it did not fit the generic definition and should logically be assigned to a new genus. Nevertheless, as it comprised only three specimens including the holotype, all damaged, it seemed undesirable to establish a monotypic taxon on a material in such poor condition. The species was provisionally retained in Acanthaxius ( Ngoc­Ho, 2005).

According to Kensley (1996), the advanced characters of the genus are the relatively slender and dentate rostrum, with its basal pair of spines in a supraorbital position; the form of the pereopod 1 chela, and especially that of the small pereopod 1, with slender dentate fingers being 1.5–2.0 times longer than the propodal palm; the presence of spines on the upper margins of the dactylus and propodus of the pereopod 1 chela; the absence of pleurobranchs; and the presence of epipods on pereopods 1–4.

The new species studied agree well with this scheme except for the fingers of the pereopod 1 in A. gadaletae n. sp. being only about 1.2–1.3 longer than the palm. It can also be noted that all known Acanthaxius species have a slender and incurved tip of the antennal article 2, as pointed out by Sakai & de Saint Laurent (1989), which could be considered as diagnostic.