Acanthaxius ningaloo, 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 : 234-237

Acanthaxius ningaloo sp. nov.

Figures 9 , 10 , 38

Material examined. Holotype. WA, off Ningaloo North, 21°59.10'S, 113°49.12'E – 21°59.47'S, 113°49.08'E (stn SS10-2005 153), 165 m, 11 Dec 2005, NMV J53446 (female, cl. 22.2 mm, tl. 56.7 mm).

Paratype. Collected with holotype, NMV J53447 (male, cl. 16 mm, complete but fragmented) .

Description of female holotype. Carapace heavily spinulose. Rostrum 0.4 times length of front-to-cervical groove, acute, with 3–4 lateral spines anterior to supraocular spine, continuous with definite lateral gastric carinae. Supraocular spines prominent. Lateral gastric carina with 9 spines. Submedian gastric carina duplicated, external row with 7–10 spines, internal with 12–13 spines. Median gastric carina with 21 spines. Sternite 7 (pereopod 4) deeply divided in midline over posterior two-thirds and with sharp oblique lateral ridge. Sternite 8 (pereopod 5) with setose semicircular flap on anterior face at base of leg. Abdominal pleuron 1 twice as deep as middorsal length, ventrally acute; pleuron 2 broad, lateral length 1.2 times dorsal length, anteroventrally rounded; pleura 3–5 becoming more ventrally acute; pleuron 6 with small spine on ventral margin; pleura 1–5 with lateral crease.

Eyestalk 0.8 length of rostrum; cornea weakly pigmented. Antennular peduncle reaching to proximal part of antennal article 5. Antennal article 1 with 1 spine and 2 spinules on lower distal margin; article 2 distal spine slender, directed slightly inwards, reaching distally to middle of antennal article 4; scaphocerite slender, straight, reaching distally almost to end of article 4; article 3 with 4 spines on mesial lower margin; article 4 about half length of article 2 (excluding distal spine), with distoventral spine; article 5 about two-thirds length of article 4. Maxilliped 3 basis with 1 spine; ischium with 2 spines on lower margin; crista dentata with 16 teeth; merus with 3 spines on lower margin; carpus unarmed.

Pereopods 1 scarcely differentiated, of similar length, propodus of major more swollen. Major pereopod 1 (right) coxa lower margin with 2 spines; basis lower margin with 1 spine; ischium lower margin with 4 spines; merus upper margin convex, with 4 spines, lower margin with 9 spines, lateral face spinose distally, mesial face spinose distally; carpus upper margin with 6 spines, lower margin with 4 spines laterally, 1 spine mesially, lateral face spinose, mesial face with 1 spine; propodus upper margin with 2 rows each of 4 spines, lower margin with 21 spines in lateral row and 8 spines in mesial row, lateral face spinose, mesial face tuberculate, with 8 spines concentrated near gape; fixed finger twice length of upper palm, cutting edge straight, with c. 20 irregular rounded teeth; dactylus upper margin with 9 spines, lateral face with proximal row of 5 submarginal spines, mesial face with proximal spine and row of denticles, cutting edge as in fixed finger; both fingers bearing setae.

Minor pereopod 1 coxa, ischium and merus as in larger cheliped; carpus upper margin with 4 spines, lower margin with 1 spine, lateral face spinose, mesial face with 1 spine; propodus upper margin with 2 rows each of 4 spines, lower margin with 23 spines in lateral row and 5 spines in mesial row, lateral face spinose, mesial face tuberculate, with 6 spines concentrated near gape; fixed finger 2.5 times length of upper palm, cutting edge with c. 30 oblique sharp teeth; dactylus upper margin with 10 spines, lateral face with proximal row of 5 submarginal spines, mesial face with row of denticles, cutting edge as in fixed finger; both fingers setose as in major pereopod.

Pereopod 2 ischium lower margin with 1 distal spine; merus lower margin with 3 spines; carpus slightly shorter than chela; propodus upper margin 0.8 length of dactylus. Pereopod 3 merus lower margin with 3 spines; propodus 2.8 times as long as dactylus, with 6 marginal robust setae (some duplicated). Pereopod 4 merus lower margin with 4 spines; propodus 2.6 times as long as dactylus, with 7 marginal robust setae (some duplicated). Pereopod 5 propodus 2.9 times as long as dactylus, subchelate, with short fixed finger; dactylus with broad blade on cutting edge.

Pleopods 2–5 appendix interna one third length of endopod.

Telson about as long as broad, lateral margin with 1 spine, distal margin convex with posteromedian spine, posterolateral angle with 1 or 2 minute teeth and 2 robust setae; dorsal face with 2 spines in each oblique row. Uropodal endopod 1.6 times as long as wide, with 3 lateral spines, longitudinal ridge with 3 spines (including marginal). Uropodal exopod 1.6 times as long as wide, with 4 lateral spines, 2 longitudinal ribs (outer rib with 2 spines), posterolateral angle with 1 fixed spine and 1 robust seta; transverse suture with 7 spines.

Male. Carapace spination and abdomen indistinguishable from female. Pereopods 1 grossly differentiated, of similar length, propodus of major considerably more swollen than minor. Major pereopod 1 (right) coxa lower margin with 2 small spines; basis lower margin with 1 spine; ischium lower margin with 5 spines; merus upper margin convex, with 4 spines, lower margin with 10 spines, lateral face spinose distally, mesial face spinose distally; carpus upper margin with 6 spines, lower margin with 3 spines laterally, 1 spine mesially, lateral face spinose and densely setose in upper half, mesial face with 1 spine; propodus upper margin with 2 rows each of 4 spines (mesial row obsolete), lower margin with 19 spines in lateral row and 14 spines in mesial row, diminishing, lateral face spinose and densely setose in upper half, mesial face tuberculate, with 8 spines concentrated near gape; fixed finger as long as upper palm, cutting edge straight, with c. 20 irregular rounded teeth; dactylus upper margin with 6 spines, lateral face with proximal row of 5 small submarginal spines, densely setose, mesial face with proximal spine and row of denticles, cutting edge as in fixed finger.

Minor pereopod 1 coxa, ischium and merus as in larger cheliped; carpus upper margin with 4 spines, lower margin with 3 lateral spines, 1 mesial spine, lateral face spinose and setose, mesial face with 1 spine; propodus upper margin with 2 rows of 4 lateral and 3 small mesial spines, lower margin with 20 spines in lateral row and 5 spines in mesial row, lateral face spinose and setose, mesial face tuberculate, with 6 spines concentrated near gape; fixed finger 4 times length of upper palm, cutting edge with c. 30 oblique sharp teeth; dactylus upper margin with spinose (broken).

Pleopod 2 with appendix masculina about third length of endopod, attached one-third along; appendix interna slightly shorter than appendix masculina.

Etymology. Ningaloo, the name of a major WA fringing reef, is from the local Gnulli language.

Distribution. WA, off Ningaloo North, 22°S, 114°E, 165 m depth (known only from the type locality).

Remarks. Acanthaxius ningaloo is most similar to A. polyacantha ( Miyake and Sakai, 1967) described from the East China Sea, also recorded from the Solomon Islands by Ngoc-Ho (2006), and to A. formosa from off Taiwan ( Kensley and Chan, 1998). The type specimen is a female of similar size to the holotype of the other three species; the Solomon Islands specimen is much smaller. All species share a carapace covered with spinules and duplicated submedian gastric carinae. Acanthaxius ningaloo has a longer rostrum with four (as in A. formosa , rather than two as in A. polyacantha ) pairs of lateral spines, antenna article 3 with four spines (rather than one as in the other two species), relatively shorter telson, more pronounced spines along the margin of the cervical groove and more definite spines on the postcervical carapace. The spines along the margins of the fingers of the chelipeds are apparently longer and more erect. Further, A. formosa lacks denticles anterolateral to the cervical groove. Acanthaxius miyazakiensis , reported from Japan, Philippines and New Caledonia ( Sakai and de Saint Laurent, 1989), is similar to all three but has a more elongate minor first cheliped and fewer carapace spinules.

Acanthaxius ningaloo has strongly sexually dimorphic chelipeds, the major one of the male being more setose, more swollen than the minor, and with shorter marginal spines than the female. In no species described to date has both sexes been illustrated. Most figures are of females but the male of A. grandis , a species with a similar cheliped but smooth carapace, would appear to be of the grossly swollen form ( Kensley and Chan, 1998).

Figures

Figure 9. Acanthaxius ningaloo sp. nov. a, lateral view. b, dorsal view of carapace, peduncles of antennule and antenna. c, telson and right uropod. d, sternites 7 and 8. e, left sternite 8 (lateral). f, left antenna peduncle (lateral). g, epistome, left antennule and antenna (ventral). h, female major pereopod 1 (right, dislocated, lateral). i, same (carpus–dactylus, without setae, mesial). j, female minor pereopod 1 (left, dislocated, without setae, lateral). k, same (carpus–dactylus, without setae, mesial). All figures from holotype.

Figure 10. Acanthaxius ningaloo sp. nov. a, maxilliped 3. b–e, pereopods 2–5 (right except d). f, female pleopod 1. g, male pleopod 2 (rami without setae). h, male major pereopod 1 (right, dislocated, lateral). i, same (propodus–dactylus, without setae, mesial). j, male minor pereopod 1 (left, dislocated, without setae, lateral). k, same (propodus–dactylus [broken], without setae, mesial). Figs a–f from holotype; figs. g–k from paratype NMV J53447.

Figure 38. Acanthaxius ningaloo sp. nov. Photomicrographs of (left to right) maxilla 1, maxilla 2 (posterior epipod seta missing), maxilliped 1, maxilliped 2.