Neaxius Borradaile, 1903

Poore, Gary C. B. & Dworschak, Peter C., 2018, The Indo-West Pacific species of Neaxiopsis and Neaxius (Crustacea: Axiidea: Strahlaxiidae), Memoirs of Museum Victoria (Mem. Mus. Vic.) 77, pp. 15-28 : 16-17

Neaxius Borradaile, 1903

Axius (Neaxius) Borradaile, 1903: 537 .—De Man, 1925c: 12. Neaxius . — Sakai and de Saint Laurent, 1989: 29.— Poore, 1994:

100.— Sakai, 1994: 176.— Sakai, 2011: 324–325.

Type species. Axia acantha A. Milne-Edwards, 1879 , by original designation.

Remarks. Specimens of the type species, now N. acanthus (A. Milne-Edwards, 1879) from the type locality, New Caledonia, have never been illustrated, and Milne-Edwards’ (1879) description is too general to be certain of the species’ identity: he described the antenna as having four or five lateral spines, the anterior carapace margin with four or five spines, the cervical groove with three or four spines, and the scaphocerite with one mesial and four lower spines. This description applies to many specimens throughout the Indo West-Pacific and the species has been assumed to be widespread. The standard reference for details of this species is De Man’s (1898) description and illustrations of specimens from Sulawesi, Indonesia, not those from the type locality. Sakai and de Saint Laurent (1989) were the first to include type material in their appraisal of N. acanthus .

Borradaile (1903) synonymised without comment Eiconaxius taliliensis Borradaile, 1900 , with N. acanthus . Axius acanthus var. mauritiana Bouvier, 1914 , has also long been thought to be a junior synonym. This synonymy was accepted by Ngoc-Ho (2006) who tabulated differences between the six accepted species of Neaxius , three from the Indo-West Pacific and three from the Atlantic Ocean.

Sakai (2011: 329–330, figs 61, 62) took a different view and treated all nominal Indo-West Pacific species and subspecies – Axia acantha (type locality: New Caledonia), Eiconaxius taliliensis (New Britain), Neaxius trondlei Ngoc-Ho, 2005 (Marquesas Islands) and Axius acanthus var. mauritianus ( Mauritius) – as synonyms of Axius glyptocercus von Martens, 1868 (Cape York, Qld, Australia), which he believed to be a variable species. He described and figured the antenna, carapace spination and scaphocerite of specimens from Fiji, Tahiti, Palau, Sulawesi and Ryuku, Japan, to justify that only one species, Neaxius glyptocercus , was distributed widely in the Indo-West Pacific. He argued that the variability in a population of N. acanthus from Motupore, Papua New Guinea, studied by Mukai and Sakai (1992) (5–7 spines on the cervical groove, 1 or 2 mesial and 3–6 lateral spines on the second antenna article, spinose merus on pereopod 2) supports his view, but in reality, they confirm the opposite. This population differs consistently from N. glyptocercus in having the cervical groove, antenna article and pereopod 2 unarmed as in all Australian specimens examined by Poore and Griffin (1979) and in more recently examined examples ( AM, NMV, NHMW, ZMH). To these characters can be added differences in the shape and ornamentation of the telson. The telson of N. glyptocercus is c. 1.3 times as wide as long, moderately tapering, with 1 or 2 small spines along the lateral margin, with the anterior transverse ridge reaching the lateral margins, and the posterior concave face without ornamentation. The telson of N. acanthus is 1.5 times as wide as long, strongly tapering, with 1–6 tubercles above each posterolateral margin, with the second transverse ridge one-third of the way between the first and the posterior margin, and with a third short obsolete transverse ridge and longitudinal lateral buttresses emerging from the ends of the second transverse ridge.

This separation is, however, confused by the discovery that southern and Pacific representatives of “ N. glyptocercus ” are morphologically distinct and warrant description of another species, Neaxius capricornicus sp. nov. This confusion has led to errors in the identification of species for which sequences are registered in Genbank at the National Center for Biotechnology Information (https://www.ncbi.nlm.nih.gov/nuccore/neaxius) ( Table 1 ).

Tsang et al. (2008) showed on the basis of three rRNA sequences that N. acanthus from Taiwan differs from N. capricornicus from Australia (wrongly identified as N. glyptocercus ) with 100% probability.

Anker et al. (2015) illustrated in colour specimens of what are clearly N. acanthus from Lombok, Indonesia, as N. glyptocercus , but expressed confusion over Sakai’s synonymy. Sakai (2017) repeated his incorrect diagnosis of “ N. glyptocercus ” and figured a cheliped from Japan clearly of the N. acanthus form.

The four Indo-West Pacific species of Neaxius are here diagnosed with the same character suite. Major diagnostic characters of N. acanthus , N. capricornicus sp. nov. and N. glyptocerus are compared in fig. 8. The distributions of all species in the Indo-West Pacific are shown in fig. 9.