Eiconaxius vaubani, Poore, Gary C. B., 2017

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 : 372-375

Eiconaxius vaubani sp. nov.

( Figs 4–6 )

Type material. Holotype: Madagascar. Off SE coast, 25°80.9'S, 47°21'E, 255 m, RV Vauban stn 65, Tabachnik colln, 1994, in external canal of hexactinellid sponge, MNHN IU- 2016-8133 (male, 3.8 mm).

Description of male holotype. Carapace smooth. Rostrum 0.2 times length of carapace length, concave dorsally, apex depressed below level of median carina, tapering to acute tip from lateral base of eyes, median distal ridge vertical-oblique, with small tooth, lateral margins converging, meeting median anterior rostral ridge at their most elevated level, unarmed, continuous with lateral gastric carinae. Lateral gastric carina unarmed, reaching about halfway to cervical groove. Submedian gastric carina smooth, obsolete, together converging on sharp median corner. Median gastric carina an obsolete broad triangular plate. Pleuron 1 triangular; pleuron 2 oblique-truncate, posteroventrally with sharp angle; pleura 3–4 truncate, posteroventrally acutely produced, each with minute anteroventral tooth; pleuron 6 subacute; pleonite 6 dorsal posterior margin smooth.

Eyestalk, little more than half length of rostrum; cornea unpigmented. Antennular peduncle reaching to end of antennal article 4; article 1 unarmed. Antennal article 1 unarmed; article 2 stylocerite a vertical blade, reaching to midpoint of article 4; scaphocerite a vertical blade, reaching just beyond end of article 4; articles 3 and 4 unarmed. Maxilliped 3 endopod missing on both sides, with elongate exopod.

Major cheliped ischium lower margin irregularly toothed; merus lower margin with 1 small distal tooth, upper margin convex; carpus lower margin with 1 distal tooth; propodus upper margin length 1.25 times greatest height; upper margin smooth, ending in 2 short carinae, lower margin smooth; fixed finger 0.4 times as long as upper palm, cutting edge with irregular rounded teeth, most prominent over proximal third; dactylus upper margin strongly convex, with double carinae, cutting edge irregular, most prominent tooth truncate near apex.

Minor cheliped more slender than major; ischium lower margin with small distal tooth; merus upper margin convex, lower margin with 3 small teeth; carpus lower margin with 1 distal tooth; propodus upper margin length 1.2 times greatest height; upper margin smooth, lower margin smooth, lateral face with oblique ridge running on to fixed finger and ending in 2 blunt teeth; mesial face with oblique curved ridge running on to fixed finger and ending in blunt tooth, distal margin (dactylus articulation) oblique, with 2 minute teeth laterally, with 2 small teeth mesially; fixed finger third length of upper palm, cutting edge with irregular teeth; dactylus tapering, cutting edge with basal tubercle, otherwise smooth.

Pereopod 2 ischium lower margin unarmed; merus lower margin unarmed; carpus 1.2 times length of propodus upper margin; propodus upper margin 1.3 times as long as dactylus. Pereopod 3 merus unarmed, widest at midpoint, 3.3 times as long as wide; propodus 2.0 times as long as dactylus, with 6 transverse rows of 2 or 3 spiniform setae; dactylus ovate, with 7 marginal spiniform setae along oblique margin, plus unguis, 13 facial spiniform setae in rows of 8 and 4. Pereopod 4 merus unarmed, parallel-sided, 5.2 times as long as wide; dactylus ovate, with 7 spiniform setae along oblique margin, plus unguis, 16 facial setae in irregular rows of 9 and 7. Pereopod 5 propodus 2.3 times as long as dactylus, simple, distally densely setose, with 1 distal spiniform seta; dactylus spatulate, with 7 spiniform setae along oblique margin, plus unguis, 4 facial spiniform setae in 1 row.

Pleopod 1 a simple elongate article. Pleopods 2–5 each with appendix interna 0.3 length of endopod. Pleopod 2 of male appendix masculina 0.9 times as long as appendix interna, broader, with terminal setae.

Telson 1.1 times as long as wide, widest proximally, then tapering evenly to 0.7 of maximum width, lateral margin with irregular small teeth, distal margin a shallow obtuse angle between weak distolateral teeth, with pair of distolateral spiniform setae, with posteromedian spine; dorsal face with 3 pairs of small spines. Uropodal endopod 2.0 times as long as wide, elongate-oval, with 11 teeth along anterior margin, most distal ones larger and produced beyond curved posterior margin. Uropodal exopod 1.45 times as long as wide, oval with c. 15 small irregular teeth on anterior margin, last tooth distal, with apical spiniform setae, posterior margin convex, smooth.

Etymology. The species is named for the French oceanographic research vessel, RV Vauban.

Distribution. Off Madagascar, SE coast, 255 m; in canal of hexactinellid sponge (known only from the type locality).

Remarks. Eiconaxius vaubani is an atypical species of Eiconaxius but shares with all others no suture on the uropodal exopodal, no supraocular spines and submedian gastric carinae, an unarmed lateral gastric carina, swollen chelipeds and spatulate dactylus on pereopod 5, pleopods 3–5 with appendices internae and an appendix masculina on the male pleopod 2. It differs from all other species most obviously in the shape of the rostrum, chelipeds and pereopod 4. The apex of the rostrum of typical species of Eiconaxius is formed of the confluence of its lateral margins (e.g., Figs 2 a, b). The rostrum of E. vaubani is produced anteroventrally beyond the confluence of its lateral margins ( Figs 4 a, b, 5a, b). The fixed finger of the minor cheliped of E. vaubani is triangular with a broad base as in typical Eiconaxius but is one third of the length of the upper palm ( Figs 4 , 3 e–h) whereas in most Eiconaxius the fixed finger is as long or longer than the palm. Two species of Eiconaxius are exceptional in this regard: the fixed finger of E. kimbla Kensley, 1996 (male pleopod 1 absent), and of E. heinrichi ( Sakai, 2011) (male pleopod 1 present) are significantly shorter than the upper palm. The merus of pereopod 4 of E. vaubani is narrower and 1.4 times as long as the meri of pereopods 2 and 3 ( Fig. 6) whereas in other species of Eiconaxius the meri of pereopods 2–4 are of similar proportions and lengths. The male pleopod 1 is a simple article ( Fig. 5 c) whereas, except for at least the five species listed above, it is absent in most species of Eiconaxius .

While it is tempting to erect a new genus for this species doing so would lead to probable paraphyly of those species remaining in Eiconaxius .

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.