Eiconaxius Spence Bate, 1888

Poore, Gary C. B., 2017, Synonymy and problematic species of Eiconaxius Spence Bate, 1888, with descriptions of new species (Crustacea: Decapoda: Axiidea: Axiidae), Zootaxa 4231 (3), pp. 364-376 : 365-366

Eiconaxius Spence Bate, 1888

Eiconaxius Spence Bate, 1888: 40 .— Stebbing 1893: 188 –189.—Sakai & de Saint Laurent 1989: 15 –16.— Sakai & Ohta 2005: 69 –70.— Poore & Collins 2009: 255 .— Sakai 2011: 268.

Iconaxiopsis Alcock, 1901: 193 .— Balss 1925: 210 –211 [type species: Eiconaxius kermadeci laccadivensis Alcock & Anderson, 1894 , subsequent designation by Borradaile (1903: 537)].

Axius (Iconaxiopsis) .— Borradaile 1903: 537.

Axius (Eiconaxius) .— Borradaile 1903: 537 –538.—De Man 1925b: 14.

Eiconaxiopsis Sakai, 2011: 290 [type species: Eiconaxiopsis heinrichi Sakai, 2011 , by original designation].

Type species. Eiconaxius acutifrons Spence Bate, 1888 [subsequent designation by Stebbing (1893: 188)].

Diagnosis. Gonochoristic. Carapace smooth; cervical groove inconspicuous. Rostrum triangular, concave dorsally, not especially depressed below level of carapace, about twice as long as eyestalks, lateral margins smooth or denticulate, continuous with definite lateral carinae. Supraocular spines absent; lateral gastric carinae unarmed; submedian gastric carinae absent; median carina denticulate or smooth, not extending posteriorly over broad triangular midgastric region; postcervical carina absent. Pleon smooth, tergum and pleura continuous; pleuron 1 rounded, pleuron 2 acute or subacute, pleura 3–5 triangular, with or without anteroventral tooth. Eyestalk at most twice as long as cornea diameter; eye pigmented or not pigmented or weakly pigmented. Antenna, scaphocerite simple, straight, almost as long as article 4. Pleurobranchs present above pereopods 2–4; arthrobranchs well developed; epipods and podobranchs present, epipods fully developed on pereopods 1–4, podobranchs on 1–3. Maxilliped 3, exopod not clearly bent at base of flagellum. Pereopods 1 unequal. Major cheliped massive, palm swollen, fingers shorter than palm. Minor cheliped merus with smooth or denticulate lower margin; palm without single sharp tooth on lateral face proximal to base of fingers, with broadly-based tapering fixed finger; curved dactylus longer than palm upper margin; with setae only on fingers. Pereopods 3 and 4, dactyli ovate or spatulate, each with single row of marginal spiniform setae plus few–many supplementary lateral spiniform setae. Pereopod 5 dactylus spatulate, with oblique margin having single row of spiniform setae, with or without facial spiniform setae. Pleopods 2–5 exopod lanceolate, not laterally lobed, endopod with appendix interna. Pleopod 1 of male present or absent. Pleopod 2 of male with digitiform appendix masculina and appendix interna. Telson suboval, usually longer than wide; lateral margin serrate; posterior margin rounded or truncate, with or without median spine. Uropodal endopod oval, anterior margin serrate, distal margin curved, continuous with anterior and posterior margins (rarely lobed); exopod oval, anterior margin serrate, without transverse suture.

Remarks. Stebbing (1893) was the first to designate Eiconaxius acutifrons Spence Bate, 1888 as type species of Eiconaxius , not Borradaile (1903) as stated by Sakai & de Saint Laurent (1989) and Sakai (2011). Eiconaxius acutifrons was described in detail by Komai & Tsuchida (2012) who also provided a detailed synonymy listing misuses of the species name.

Alcock (1901) differentiated Iconaxiopsis from Eiconaxius (misspelled as Iconaxius ) in the exopod of maxilliped 2 being much longer than the endopod (similar lengths in Eiconaxius ), an arthrobranch, epipod and podobranch on maxilliped 2, and pleurobranchs on thoracomeres 5–7 (above pereopods 2–4) (none present in Eiconaxius ). Borradaile (1903) repeated these characters to distinguish the two taxa as subgenera of Axius . De Man (1925b) synonymised the two on the grounds that the status of the arthrobranch on maxilliped 2 was unknown for most taxa and it could not be seen on the only species that he examined. Pleurobranchs are present above pereopods 2–4 and epipods present on maxilliped 2 on all species of Eiconaxius available for this study so the two genera can not be distinguished on these grounds.

Trybom (1904) misspelled Eiconaxius as Euconaxius and described Euconaxius coronatus and Euconaxius crassipes as new, both now Calocarides coronatus ( Trybom, 1904) , type species of that genus. Lagerberg’s (1908) use of Eiconaxius is in this sense.

Sakai (2011) separated his new species Eiconaxiopsis heinrichi from Eiconaxius consobrina (De Man, 1907) on the basis of two characters that he then used to justify a new genus: (1) dactyli of pereopods 3–4 are ‘simple, tapering distally, and pointed distally’ (versus ‘short, subspatulate in form, and spinulose on the ventral margin’); (2) the male pleopod 1 is a ‘bisegmented appendage’ (versus absent). He added two more characters to justify placing Eiconaxiopsis in its own family, Eiconaxiopsididae : (3) the carapace possesses a median carina ‘gradually broadening posteriorly’ (versus ‘with or without denticles, which is simple or bifurcate posteriorly’ in Eiconaxius ); (4) the telson lacks a median spine (versus with a spine),

None of these characters is reliable at generic or family levels:

(1) As explained below, the dactyli of pereopods 3 and 4 of Eiconaxiopsis heinrichi are not as described and figured by Sakai (2011: fig. 56D). They have a single row of marginal spiniform setae with few supplementary lateral spiniform setae ( Figs 1 i, j) as is the case in the type species ( Komai & Tsuchida 2012: fig. 2) and most species of Eiconaxius available for this study. This would seem to be how most species descriptions and illustrations could be interpreted. Eiconaxius agassizi ( Bouvier, 1905) , E. parvus Spence Bate, 1888 and E. vaubani sp. nov. are typical ( Figs 1 a, b, 3c, d, 6b, c). Eiconaxius borradailei ( Bouvier, 1905) ( Figs 4 c, d) and E. sibogae (De Man, 1925a) ( Figs 1 e, f) differ from all others for which detail is available in having multiple (maximum three) rows of spiniform setae in a tear-shaped marginal area on the dactyli of pereopods 3 and 4.

(2) The presence or absence of the male pleopod 1 is not explicitly stated for most described species of Eiconaxius . Most of those for which information is available, including the type species, lack a male pleopod 1 but my own observations confirm that males possess a pleopod 1 of one article in Eiconaxius borradailei , E. sibogae ( Fig. 1 h) E. vaubani sp. nov. ( Fig. 5 c) or of two articles in E. heinrichi ( Fig. 1 k). Alcock (1901) described Iconaxiopsis as having ‘in the male ... appendages of the 1st [abdominal] somite ... uniramous’. Pleopod 1 is shown in illustrations of syntypes of both included species, of E. andamanensis Alcock, 1901 in the original paper and of E. laccadivensis ( Alcock & Anderson, 1894) in Alcock & MacGilchrist (1905) . However, MacGilchrist (1905) commented that the male pleopod 1 was wanting in E. laccadivensis and well developed in E. andamanensis . Sakai (2011) included only E. heinrichi and E. sibogae in Eiconaxiopsis .

(3) The median carina is confined to the rostrum, meeting the gastric region posteriorly in all species; it varies only slightly. Sakai’s (2011: figs 56a, b, c) are misleading.

(4) The telson spine varies between individuals of the same species, as Sakai (2011: 295) himself acknowledged for E. sibogae .

Separation of a second genus from Eiconaxius on one or other of these characters is premature but both Iconaxiopsis Alcock, 1901 and Eiconaxiopsis Sakai, 2011 are potential available names.

Sakai (2011) included two problematic taxa in his catalogue of species of Eiconaxius . Each is discussed below.

Figures

FIGURE 4. Eiconaxius vaubani sp. nov. Holotype, MNHN IU- 2016 - 8133. a, b, habitus. c, d, mesial views of major and minor chelipeds respectively. e, f, lateral views of major and minor chelipeds respectively. Photos by N. Mollaret, MNHN.