Eiconaxius parvus 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 : 368-371

Eiconaxius parvus Spence Bate, 1888

( Figs 2, 3)

Eiconaxius parvus Spence Bate, 1888: 44 –46, pl. 5 figs 4, 5.—Sakai & de Saint Laurent 1989: 18.— Kensley 1996: 475.— Poore & Collins 2009: 260, fig. 25.

Axius (Eiconaxius) parvus .— Borradaile, 1903: 538.—De Man, 1925b: 4, 16 (part).

Iconaxius parvus . — Balss, 1925: 210.

Not Axius (Eiconaxius) parvus .—De Man, 1925b: 42–44, pl. 3 fig. 7 (record off SW Kei I., 5°53.8'S, 132°48.8'E = E. demani Sakai, 1992 ).

Type material. Holotype: Kermadec Is., 29°55'S, 178°14'W, 951 m, NHMUK 1888.22 (female with 7 brephalos larvae attached, 12 mm).

Other material examined. Fiji, Lau Archipelago, Yangasa Cluster, 18°50'S , 178°27'W, 777–787 m, (BORDAU 1 stn CP1491), MNHN IU-2016-8025 (male, 4.3 mm); MNHN IU-2016-8026 (female, 4.5 mm); MNHN IU-2016-8027 (39 females, 4.3–5.1 mm); MNHN IU-2016-8028 (21 males, 3.6–4.5 mm); 18°51'S, 178°32'W, 785–820 m (BORDAU 1 stn CP1490), MNHN IU-2016-8031 (6 males, 9 females, 4.8–5.5 mm); 18°43'S, 178°23'W, 430–450 m (BORDAU 1 stn DW1492), MNHN IU-2016-8029 (male, 5.0 mm). Off Lakeba I., 18°47'S, 178°47'W, 750–767 m (BORDAU 1 stn CP1460), MNHN IU-2016-8030 (10 males, 13 females, 3.2–4.9 mm).

Wallis and Futuna Islands, 13°39'S, 179°56'E, 650–700 m (MUSORSTOM 7 stn DW636), MNHN IU- 2016- 8032 (female, 6.0 mm).

Description. Carapace smooth. Rostrum 0.2 carapace length, concave dorsally, parallel-sided over eyes, tapering to acute tip, with obscure tubercles on oblique margins, depressed below level of median carina, continuous with lateral carinae. Lateral gastric carina unarmed, with short hiatus between anterior ridge and short posterior section. Submedian gasric carina smooth, together semicircular and converging on median carina.

Median gastric carina obsolete, on base of rostrum only. Pleuron 1 ventrally rounded; pleuron 2 oblique angled, posteroventrally acutely produced; pleura 3, 4 posteroventrally acutely produced, pleuron 5 rounded, all without anteroventral tooth; pleuron 6 with acute posteroventral angle; pleonite 6 dorsal posterior margin microscopically denticulate.

Eyestalk 0.5 length of rostrum; cornea weakly pigmented. Antennular peduncle reaching almost end of antennal article 4; article 1 unarmed. Antennal peduncle article 1 unarmed; article 2 stylocerite a vertical blade, reaching just beyond end of article 4; scaphocerite a vertical blade, reaching to end of article 5; article 3 lower margin with mesial tooth; article 5 about half length of article 4. Maxilliped 3 coxa with mesial spine; ischium unarmed; crista dentata of about 14 similar teeth; merus and carpus unarmed; exopod a single article half as long as ischium.

Major cheliped merus lower margin with few irregular teeth, 2 spines distally, upper margin with minute tooth; carpus lower margin with distal tooth; propodus upper margin carinate, with small distal tooth, length 1.1 greatest height, lower margin smooth, lateral face smooth, mesial face with few tubercles distally; fixed finger 0.6 times as long as upper palm, cutting edge almost smooth, with longitudinal mesial ridge; distolateral margin of palm with upturned blade-like tooth and smaller more mesial tubercle in gape; dactylus distally curved, upper margin carinate, cutting edge smooth.

Minor cheliped shorter and more slender than major, palm 0.7 times height of major palm; merus lower margin with few irregular teeth, 2 spines subdistally; carpus lower margin with distal tooth; propodus dilating, upper margin carinate, 0.9 times greatest height, lower margin smooth, lateral and mesial faces smooth; fixed finger 1.3 times length of upper palm, cutting edge almost smooth, with longitudinal mesial ridge; distolateral margin of palm oblique, with prominent triangular tooth in gape; distomesial margin of palm oblique, with obsolete tubercle in gape; dactylus distally curved, upper margin carinate, cutting edge smooth.

Pereopod 2 ischium lower margin unarmed; merus lower margin unarmed; carpus 0.8 length of propodus upper margin; propodus upper margin twice as long as dactylus. Pereopod 3 merus unarmed; propodus 2.5 times as long as dactylus, with 5 rows of 1 or 2 spiniform setae; dactylus spatulate, with 11 spiniform setae along oblique margin, plus unguis, and 4 facial spiniform setae. Pereopod 4 virtually identical to pereopod 3; propodus 2.3 times as long as dactylus, with 6 rows of 1–3 spiniform setae; dactylus spatulate, with 10 spiniform setae along oblique margin, plus unguis, and 3 facial spiniform setae. Pereopod 5 propodus 2.4 times as long as dactylus, simple, distally densely setose, without spiniform setae; dactylus spatulate, with 8 spiniform setae along oblique margin, plus unguis.

Telson of male 1.4 times as long as wide, of female 1.55 times as long as wide, widest at midpoint, tapering to indeterminate posterolateral angles, lateral margin obscurely denticulate, distal margin evenly curved, with posteromedian spine; dorsal face with obsolete longitudinal ridges. Uropodal endopod 2.35 times as long as wide, oval, anterior margin with 7 teeth over distal half, last tooth distal, without longitudinal ridge. Uropodal exopod 1.8 times as long as wide, oval, anterior margin with 15 small irregular teeth over distal two-thirds, last tooth distal, without longitudinal rib.

Variation. In some females the maxilliped 3 exopod is as long as the ischium but others have intermediate lengths. The two teeth on the distolateral margin of the major cheliped palm may be variously fused but the larger one is always more lateral than the lower smaller one, with a concave or square upper margin and with convex distal-lower margin ( Figs 2 g, h). The prominent triangular tooth on the distolateral margin of the minor cheliped palm may have a bifid apex ( Fig. 2 i) and the tubercle on the distomesial margin may be duplicated ( Fig. 2 j).

Distribution. New Zealand, Kermadec Is; Fiji, Lau Archipelago; Wallis and Futuna; 430–952 m depth.

Remarks. Spence Bate (1888) stated that he had ‘but one specimen of this species’ and superficially illustrated it, an ovigerous female. He also figured a brephalos larva in one of seven attached ‘ova’. Sakai & de Saint Laurent (1989) erroneously listed ‘seven ovigerous females’, one of which they selected as a lectotype ( Sakai, 2011). Poore & Collins (2009: fig. 25) illustrated the female as the holotype which seems the more sensible status. The highly characteristic tooth and lobe in the gape of the major cheliped are identical to those of the new material from Fiji and Wallis and Futuna .

Eiconaxius parvus can be distinguished from other species by the characteristic upturned blade in the gape of the major cheliped. The species is similar, in as far as can be determined from illustrations, to E. asper Rathbun, 1906 from Hawaii in having a tooth in the gape of the major cheliped but lacks the denticulate crested median rostral carina. The tooth is rounded in E. asper whereas there is a larger upper-lateral upturned tooth and smaller mesial-lower tooth in the new species; the dactylar cutting edge of E. asper has a prominent basal tooth but is simple in E. parvus . Of other species in the western Pacific, E. hakuhou Sakai & Ohta, 2005 from the Sulu Sea, E. weberi (De Man, 1907) from Indonesia and E. kimbla Kensley, 1996 from off Queensland, Australia, all lack teeth in the cheliped gape, and E. kermadeci Spence Bate, 1888 also off the Kermadec Islands has complex dentition in the gape of the major cheliped and along the fixed finger of the minor cheliped.