Acanthaxius clevai, Nguyen Ngoc-Ho, 2006

Poore, Gary C. B. & Collins, David J., 2009, Australian Axiidae (Crustacea: Decapoda: Axiidea), Memoirs of Museum Victoria 66 (2), pp. 221-287 : 225

Acanthaxius clevai Ngoc-Ho, 2006

Figures 1–3 , 37

Acanthaxius clevai Ngoc-Ho, 2006: 59–62 , figs. 1, 2,

3A–C).

Material examined. WA, off Mermaid Reef, 17°11.83'S, 119°34.81'E – 17°12.37'S, 119°35.00'E (stn SS05-2007 079), 435–438 m, 18 Jun 2007, NMV J55706 (female, cl. 28.8 mm, tl. 64 mm). WA, off Point Leveque, 14°58.22'S, 121°38.56'E – 14°57.76'S, 121°38.26'E (stn SS05-2007 143), 232– 228 m, 02 Jun 2007, NMV J55705 (juvenile male, cl. 8.3 mm, tl. 20 mm) .

Diagnosis. Carapace generally smooth, with scattered setae and small tubercles dorsally. Rostrum 0.4 times length of front-to-cervical groove, acute, with 2 lateral spines anterior to supraocular spine, continuous with definite lateral gastric carinae (connecting by diverging curved ridges). Supraocular spines prominent. Lateral gastric carina with 1 spine, diverging anteriorly. Submedian gastric carina with 4 spines (last small, flattened). Median gastric carina with 3 spines. Abdominal pleuron 1 ventrally acute; pleura 2–5 posteroventrally rounded; pleuron 6 of male with small spine on anteroventral margin.

Antennal article 1 with 1 spine on lower distal margin; article 2 distal spine slender, directed inwards, reaching distally to middle of antennal article 4; scaphocerite slender, straight, reaching distally almost to end of article 4; article 3 with 1 spine on mesial lower margin. Maxilliped 3 ischium with 2 spines on lower margin; merus with 3 spines on lower margin.

Pereopods 1 well differentiated, of similar length, propodus of major cheliped more swollen than minor cheliped. Major pereopod 1 merus upper margin convex, with 2 spines, lower margin with 4 spines, lateral face spinose distally, mesial face spinose distally; carpus upper margin with 4 midline spines and 1 spine on each side, lower margin with 3 spines, mesial face tuberculate, with 1 spine; propodus upper margin with 3 midline spines and 2 spines each side, lower margin with 7 spines in lateral row and 3 spines in mesial row, lateral face tuberculate, with 5 scattered spines, mesial face tuberculate, with 4 scattered spines; fixed finger 1.2 times length of upper palm, cutting edge with large rounded teeth; dactylus upper margin with 2 erect spines, 1 submarginal spines on each side, tuberculate, cutting edge with large rounded teeth.

Minor pereopod 1 merus, carpus as in larger cheliped; propodus as in larger cheliped except narrower, lower margin with 7–9 spines in lateral row and 3 spines in mesial row; fixed finger 1.7 times length of upper palm, cutting edge straight with numerous small sharp teeth; dactylus armature as in major pereopod.

Telson rectangular, approximately parallel-sided, 1.3 times as long as wide, lateral margin with 3 spines, distal margin convex with posteromedian spine, posterolateral angle with 2 robust setae; dorsal face with 2 spines in each oblique row. Uropodal endopod 1.4 times as long as wide, with 1 lateral spine, longitudinal ridge with 4 spines (including marginal). Uropodal exopod 1.6 times as long as wide, with 7 lateral spines, 2 longitudinal ribs (outer rib with 4 spines), posterolateral angle with 1 fixed spine and 1 robust seta; transverse suture with 10 spines.

Distribution. Solomon Islands; WA, North-West continental margin, 15°– 17°S, 119°– 122°E, 228–438 m depth.

Remarks. The new material, a female and juvenile male from north-western Australia, are barely distinguishable from Ngoc-Ho’s (2006) figures and description of a similarly-sized male specimen from the Solomon Islands. We illustrate them fully and present a short diagnosis. The species is recognisable by the pattern of spination on the rostrum and carapace (two lateral rostral spines, median gastric carina with four spines, submedian with five spines including the supraorbital, and a single spine on the curved lateral gastric carina). The complex patterns of spination on the major and minor chelipeds are also virtually identical to those of the holotype. N. Ngoc-Ho illustrated the minor cheliped of a female paratype ( MNHN Th1492) for us and we detect no significant differences from our male. Slight differences in proportions (the chelipeds of the Australian adult female are slightly more slender than in the male holotype) can be attributed to sexual dimorphism. We identify the small male (about one-third as long as the adult) as the same species in spite of substantial differences in the chelipeds. The chelipeds of the small juvenile male are more elongate than those of the adult female and with more prominent spination (cf. figs. 1i–l with 3c, d). The upper margin of the dactylus possesses three spines while the Australian female and male holotype have only only two. The juvenile male possesses spinules on the anteroventral corners of abdominal pleura 3–6, not present in the adult female nor in the male holotype.

Ngoc-Ho (2006) described a second similar species, Acanthaxius gadaletae , from the Solomon Islands and New Caledonia, based on type material about half the size of specimens of A. clevai . The species, apparently adult males and females, differs from A. clevai only in better defined gastric carinae, maxilliped 3 basis with a spine, more stout pereopod 1 with four propodal and dactylar spines on the upper margins, and abdominal pleura 3–5 slightly angled posteriorly. The cheliped spination alone (more spines than in adult and juveniles of A. clevai ) is sufficient to differentiate A. gadaletae . The maxilliped 3 basis of the type of A. clevai was said to lack a distal spine and to differentiate the species from A. gadaletae ; both of the Australian specimens possess a strong spine but we don’t consider this difference alone diagnostic. This small species possesses spinules on the anteroventral corners of abdominal pleura 3–6 as in the small Australian male.

Acanthaxius gadaletae differs from the type species, A. pilocheira ( Sakai, 1987) most obviously in not having a spinose carapace and in having one, not two, spines on each lateral gastric carina.

Both specimens of A. clevai from WA lack a long straight seta on the posterior lobe of the scaphognathite (maxilla 2 epipod; fig. 37) as was reported for this species and the similar A. gadaletae ( Ngoc-Ho, 2006). The seta is typical of Axiidae and is found in all other species of Acanthaxius ( Squires, 1979; Sakai, 1987; Sakai and de Saint Laurent, 1989; own observations of four species). Only A. hirsutimana is unknown.

Figures

Figure 1. Acanthaxius clevai Ngoc-Ho, 2006. a, lateral view. b, dorsal view of carapace, peduncles of antennule and antenna. c, telson and right uropod. d, sternites 7 and 8. e, right sternite 8 (lateral). f, left antenna peduncle. g, epistome, left antennule and antenna (ventral). h, maxilliped 3 (anterior and posterior views); i, major pereopod 1 (left, lateral). j, same (propodus–dactylus, without setae, mesial). k, minor pereopod 1 (right, lateral). l, same (carpus–dactylus, without setae, mesial). All figures from NMV J55706.

Figure 2. Acanthaxius clevai Ngoc-Ho, 2006. a–d, pereopods 2–5 (right except d, with detail of dactylus of pereopod 3). e, f, female pleopods 1, 2. All figures from NMV J55706.

Figure 3. Acanthaxius clevai Ngoc-Ho, 2006. a, lateral view. b, dorsal view of carapace, peduncles of antennule and antenna. c, major pereopod 1 (left, lateral). d, minor pereopod 1 (right, lateral). All figures from NMV J55705, without setae.

Figure 37. Acanthaxius clevai Ngoc-Ho, 2006. Photomicrographs of (left to right) maxilla 1, maxilla 2, maxilliped 1, maxilliped 2.