Eiconaxius Bate, 1880

Poore, Gary C. B. & Collins, David J., 2009, Australian Axiidae (Crustacea: Decapoda: Axiidea), Memoirs of Museum Victoria 66 (2), pp. 221-287 : 255-258

Eiconaxius Bate, 1880

Eiconaxius Bate, 1888: 40 .— Sakai and de Saint Laurent, 1989:

15–16.— Sakai and Ohta, 2005: 69–70 (list of species).

Iconaxiopsis Alcock, 1901: 193–195 .— Borradaile, 1903: 537.— Balss, 1925: 210 (type species: Eiconaxius kermadeci laccadivensis Alcock and Anderson, 1894 , subsequent designation by Borradaile, 1903.

Axius (Eiconaxius) .— Borradaile, 1903: 537–538.— De Man, 1925b: 8–9 (synonymy of Iconaxiopsis ), 14.

Type species. Eiconaxius acutifrons Bate, 1888 , subsequent designation by Borradaile, 1903.

Diagnosis. Carapace smooth; cervical groove weak to inconspicuous. Rostrum triangular, broad, laterally smooth or obscurely denticulate, longer than eyestalks, depressed below level of carapace, continuous with definite lateral carinae; supraocular spines absent; lateral carina unarmed; submedian carina present, converging anteriorly and joining median carina; median carina a weak ridge on rostrum only, armed or not; postcervical carina absent.Abdominal somite 1 pleuron rounded; pleuron 2 posteriorly acute; pleura 3–5 posteriorly rounded. Eyestalk cylindrical, articulating; cornea pigmented or not. Antenna, scaphocerite blade-like. Maxilliped 3 exopod not clearly bent at base of flagellum. Pleurobranchs present above pereopods 2–4; podobranchs and arthrobranchs well developed; epipods present on maxilliped 2 to pereopod 4. Pereopods 1 asymmetrical, with propodus cylindrical; carpus-dactylus upper and lower margins smooth or toothed, propodus at least with distal tooth on upper margin. Pereopods 3–5 propodi with transverse rows of robust setae; dactyli spatulate, with row of robust setae along oblique margin. Pleopods 3–5, appendix interna present. Pleopod 1 of male absent. Pleopod 2 of male with appendix interna and appendix masculina. Uropodal exopod without transverse suture. Telson with lateral teeth, without posterolateral robust setae; apex rounded or truncate.

Remarks. Eiconaxius is a well-characterised genus of 25 similar species from deep waters in the Indo-Pacific, Caribbean and Gulf of Mexico. Sakai and Ohta (2005) erected a family, Eiconaxiidae , for the genus defining it mainly using typical generic characters. They believed the family “is conspicuously different from all other genera of the family Axiidae ” citing the chelate pereopod 2, rounded dactyli with robust marginal setae on pereopods 3–5, indistinct cervical groove and absence of the male pleopod 1. Chelate pereopods 2 are found in all axiideans. A similar “rounded” or spatulate dactylus is found on pereopod 5 of Platyaxius Sakai, 1994 (see below) but not on pereopods 3 and 4. Platyaxius also has an oval telson and uropodal rami, the exopod without a transverse suture, similar to those of species of Eiconaxius . In the telson and uropod (but not the male pleopod 1) these two genera are similar to Scytoleptus Gerstaecker, 1856 . Several axiid genera lack a male pleopod 1. Many genera lack a pleopod 1 and have an indistinct cervical groove. These similarities suggest a more complex relationship between the genera than proposed by Sakai and Ohta (2005) and we include the genus in Axiidae for now.

The median carina has been described as bifurcating posteriorly in species of Eiconaxius . We interpret the bifurcation as the two submedian gastric carinae converging anteriorly on the median carina and look to axiid genera such as Axiopsis Borradaile, 1903 for homology (see for example Ngoc-Ho, 2005).