Eiconaxius mallacoota, Poore & Collins, 2009

Poore, Gary C. B. & Collins, David J., 2009, Australian Axiidae (Crustacea: Decapoda: Axiidea), Memoirs of Museum Victoria 66 (2), pp. 221-287 : 258-260

Eiconaxius mallacoota sp. nov.

Figure 24

Material examined. Holotype. Australia, Victoria, S of Point Hicks (38°19.36’S, 149°24.18’E – 38°19.00’S, 149°27.18’E, 930–951 m (stn SLOPE 33 ), M.F. Gomon et al. on RV Franklin, WHOI epibenthic sled, 23 Jul 1986, NMV J15061 (male, cl. 5.7 mm, tl. 15.0 mm).

Paratypes. Collected with holotype, NMV J53161 (male, cl. 4.1 mm, tl. 11.0 mm); NMV J53162 (male, cl. 6.2 mm, tl. 16.8 mm). S of Point Hicks (38°21.90’S, 149°20.00’E, 1000 m (stn SLOPE 32 ), G.C.B. Poore et al. on RV Franklin, WHOI epibenthic sled, 23 Jul 1986, NMV J15060 (juvenile, cl. 2.0 mm, abdomen damaged).

Description of male holotype. Carapace smooth. Rostrum 0.25 times length of front-to-posterior margin of carapace, concave dorsally, parallel-sided over eyes, then tapering to acute tip, with 10 marginal lateral tubercles on oblique margins, depressed below level of median carina, anteriorly directed, continuous with lateral carinae. Supraocular spines absent. Lateral carina unarmed. Submedian carina smooth, together semicircular and converging on median carina. Median carina obsolete, on base of rostrum only. Abdominal somite 1 pleuron ventrally rounded-truncate; pleuron 2 oblique angled, posteroventrally acutely produced; pleura 3–4 posteroventrally acutely produced, pleuron 5 less so, all with anteroventral tooth; pleura 6 subacute; abdominal somite 6 dorsal posterior margin with pair of lateral teeth at base of telson, with (3 uneven) denticles along dorsal posterior margin.

Eyestalk 0.5 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 5; scaphocerite a vertical blade, reaching beyond end of article 5; article 3 lower margin with mesial tooth; article 4 as long as article 2; article 5 about half length of article 4. Maxilliped 3 coxa–ischium unarmed; crista dentata of about 15 similar teeth; merus and carpus unarmed.

Pereopods 1 asymmetrical, robust. Major cheliped coxa with 1 spinule; basis unarmed; ischium lower margin with few irregular teeth; merus upper margin strongly convex, with 2 small teeth, lower margin with 6 small teeth; carpus lower margin with 1 distal tooth; propodus greatest depth equal to upper margin length; upper margin with distal tooth, lower margin with 5 small teeth on lateral submarginal ridge; fixed finger 0.7 times as long as upper palm, cutting edge with irregular teeth in shallow proximal concavity, irregular tooth distally; dactylus distally curved, cutting edge smooth.

Minor cheliped more slender than major; coxa with 1 spinule; basis unarmed; ischium lower margin with few irregular teeth; merus upper margin strongly convex, with 2 small teeth, lower margin with 5 small teeth; carpus lower margin with 1 distal tooth; propodus greatest depth 1.1 times upper margin length; upper margin with distal tooth, lower margin with 4 small teeth on lateral submarginal ridge; fixed finger 1.2 times as long as upper palm, with lateral ridge parallel to cutting edge, cutting edge straight,with irregular teeth; dactylus tapering, cutting edge smooth.

Pereopod 2 ischium lower margin unarmed; merus lower margin unarmed; carpus slightly shorter than chela; propodus upper margin 3 times as long as dactylus. Pereopod 3 merus unarmed; propodus 2.5 times as long as dactylus, with 6 rows of robust setae, of 1 or 2 setae; dactylus spatulate, with 13 robust setae along oblique margin, plus unguis. Pereopod 4 virtually identical to pereopod 3; propodus 2.5 times as long as dactylus, with 6 rows of robust setae, of 1–3 setae; dactylus spatulate, with 11 robust setae along oblique margin, plus unguis. Pereopod 5 propodus 2.8 times as long as dactylus, simple, distally densely setose, without robust setae; dactylus spatulate, with 8 robust setae along oblique margin, plus unguis.

Pleopods 2–5 each with appendix interna 0.25 length of endopod. Pleopod 2 of male appendix masculina 0.7 times as long as appendix interna.

Telson 1.5 times as long as wide, widest proximally, then tapering more steeply distally, lateral margin with 8–10 small teeth, distal margin a shallow obtuse angle between weak distolateral teeth, without posteromedian spine; dorsal face with obsolete longitudinal ridges. Uropodal endopod 2.35 times as long as wide, oval, with 12 small irregular lateral teeth, last tooth distal, without longitudinal ridge. Uropodal exopod 1.6 times as long as wide, oval with 14–20 small irregular lateral teeth over distal two-thirds, last tooth distal, without longitudinal rib.

Variation. Paratype male, cl. 6.2 mm, NMV J53162 . Abdominal somite 6 posterodorsal margin with pair of lateral teeth and 2 pairs of submedian denticles. Telson with 7 small lateral teeth .

Paratype male, cl. 4.1 mm, NMV J53161. Rostrum with 5 sharp lateral teeth. Abdominal somite 6 posterodorsal margin with pair of lateral teeth, 1 pair of submedian denticles, 1 median tooth. Minor cheliped merus upper margin with 3 teeth, lower margin with 2 teeth; propodus upper margin with 2 teeth; dactylus upper margin with 1 tooth. Telson with 7 small lateral teeth.

Paratype juvenile, cl. 2.0 mm, NMV J15060. Major cheliped merus upper margin with 2 teeth, lower margin with 2 teeth; propodus upper margin with 2 teeth, lower margin with 4 teeth (all more prominent than in larger specimens). Minor cheliped merus upper margin with 1 tooth, lower margin with 1 tooth; propodus upper margin with 4 teeth, lower margin with 3 teeth; dactylus upper margin unarmed.

Etymology. Mallacoota, a township and estuary not far from the type locality (noun in apposition).

Distribution. Australia, off eastern Vic., 930–1000 m depth.

Remarks. The new species is represented by three males and one juvenile. The males vary only slightly but the juvenile has more prominent spination on the chelipeds than the others. Eiconaxius mallacoota is similar to E. kermadeci ( Bate, 1888) from a depth of 1100 m at the Kermadec Islands, north of New Zealand. The latter was redescribed by Sakai and de Saint Laurent (1989: 16–18, fig. 5) and a lectotype designated. The acute rostrum and gastric region of E. kermadeci are similarly weakly ornamented but the rostrum is shorter, not reaching to article 3 of the antennule, and less acutely tapering. The telson and uropodal rami of E. kermadeci are relatively broader than in the new species and the fixed finger of the larger cheliped is basally strongly toothed and gaping. At 37 mm long (according to Bate, or 23 mm according to Sakai and de Saint Laurent) E. kermadeci is larger than the new species but few specimens are available for either species.

Another similar species is E. parvus ( Bate, 1888) , known from a single 12 mm long ovigerous female (holotype, not lectotype as stated by Sakai and de Saint Laurent) taken at 950 m also near the Kermadec Islands. Bate’s short description and simple drawing do not allow a comparison but Paul Clark (Natural History Museum, London) kindly figured the holotype for us (fig. 25). The rostrum of E. parvus is not so clearly tapered as in E. mallacoota , the telson is relatively broader and the chelipeds slightly more elongate.

A third similar species is E. demani Sakai, 1992 from Indonesia and the Arafura Sea (just outside Australia’s EEZ) but its rostrum is apically rounded rather than acute. The only other Australian species is E. kimbla Kensley, 1996b , which differs from the new species in having an irregularly ornamented tapering rostrum, shorter telson, asymmetrical uropodal rami, and more massive elongate chelae with short fingers.

Figures

Figure 24. Eiconaxius mallacoota sp. nov. a, lateral view. b, dorsal view of carapace, peduncles of antennule and antenna. c, telson and right uropod. d, epistome, right antennule and antenna (ventral). e, maxilliped 3. f, major pereopod 1 (left, lateral). g, minor pereopod 1 (right). h–k, pereopods 2–5 (with details of dactyli of pereopods 3 and 4). l, male pleopod 2. All figures from holotype.