Acanthaxius gathaagudu, 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 : 230-234

Acanthaxius gathaagudu sp. nov.

Figures 6–8

Material examined. Holotype. WA, Shark Bay , 25°55.40'S, 112°14.35'E – 25°56.17'S, 112°14.46'E (stn SS10-2005 113), 404–407 m, 06 Dec 2005, NMV J53448 (female, cl. 36 mm, tl. 85 mm).

Paratype. WA, off Mermaid Reef, 17°01.09'S, 119°35.46'E – 17°01.81'S, 119°35.00'E (stn SS05-2007 080), 451– 440 m, 18 Jun 2007, NMV J55704 (male, cl. 22 mm, tl. 55 mm) .

Description of female holotype. Carapace smooth, with few setae. Rostrum (broken in holotype, 0.4 times length of front-to-cervical groove in paratype), acute, with 3–4 lateral spines anterior to supraocular spine, weakly continuous with lateral gastric carinae. Supraocular spines prominent. Lateral gastric carina with 2 spines. Submedian gastric carina with 4 spines. Median gastric carina with 3 anterior spines, 1 tubercle, 1 posterior spine. 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 quadrate; pleuron 6 rounded; pleura 1–5 without lateral crease, slightly flared laterally.

Eyestalk (broken in holotype, 0.5 length of rostrum in paratype); cornea pigmented. Antennular peduncle reaching to proximal part of antennal article 5. Antennal article 1 with 1 spine on distoventral margin; article 2 distal spine slender, directed slightly inwards, reaching distally to middle of antennal article 4; scaphocerite slightly curved, reaching distally to just beyond midpoint of article 4; article 3 with broad mesiodistal spine on lower margin; article 4 about two-thirds length of article 2 (excluding distal spine); article 5 about half length of article 4. Maxilliped 3 basis with 1 spine; ischium crista dentata with 15–20 teeth; merus with 4 spines; carpus unarmed.

Pereopods 1 scarcely differentiated, of similar length, propodus of major more swollen. Major pereopod 1 (right) coxa lower margin with 1 spine; basis lower margin without spine; ischium lower margin with 4 spines; merus upper margin convex, with 4 spines, lower margin with 7 spines, lateral face spinose distally, mesial face smooth; carpus upper margin with 5 spines, lower margin spinulose, lateral face spinose, mesial face with 1 spine; propodus upper margin with 1 row of 4 spines, lower margin with 18 spines in lateral row, 5 spines in proximal mesial row and 7 smaller intermediate spines, lateral face spinose, mesial face tuberculate, with 5 spines concentrated near gape; fixed finger 1.5 times as long as upper palm, cutting edge straight with c. 25 irregular rounded teeth; dactylus upper margin with (est. 5) spines, lateral face with 1 small spine, mesial face unarmed, 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 3 spines, lower margin with 2 spines, lateral face spinose, mesial face with 1 spine; propodus upper margin with 1 row of 4 spines, lower margin with 16 spines in lateral row and 4 spines in mesial row, lateral face spinose, mesial face tuberculate, with 2 spines near gape; fixed finger 2.8 times length of upper palm, cutting edge with c. 20 oblique sharp teeth; dactylus upper margin with 8 spines, lateral face with obsolete spine, mesial face unarmed, 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 2.2 times as long as dactylus, with 7 marginal robust setae (some duplicated). Pereopod 4 merus lower margin with 3 spines; propodus 2.7 times as long as dactylus, with 6 marginal robust setae (some duplicated). Pereopod 5 propodus 4 times as long as dactylus, subchelate, with short fixed finger; dactylus with broad blade on cutting edge.

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

Telson about as long as broad, lateral margin with 2 spines, distal margin broadly convex, with posteromedian spine, posterolateral angle with 1 minute tooth 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 1.7 times as long as wide, with 9 lateral spines, 2 longitudinal ribs (outer rib with 4 spines), posterolateral angle with 1 fixed spine and 1 robust seta; transverse suture with 7 spines.

Male paratype. Essentially indistinguishable from female except for: maxilliped 3 merus with 3 spines, carpus with 1 spine; details of spination of chelipeds; more slender minor cheliped; pleuron 1 having a small ventral spine, a slightly more rectangular pleuron 5 and a small spine on pleuron 6. Pleopod 2 with appendix masculina about half length of distal endopod; appendix interna slightly shorter.

Etymology. Gathaagudu is the name for Shark Bay in the local Malgana language.

Distribution. WA, North West Shelf to Shark Bay, 17°– 26°S, 112°– 119°E, 400–450 m depth.

Remarks. Comparison of the figures of the holotype (figs. 6, 7) and paratype (fig. 8) illustrates variability in spination of the carapace, maxillipeds and chelipeds. Acanthaxius gathaagudu is most similar to two other species of Acanthaxius with two spines on the lateral gastric carina. The most significant difference between them is in the number of spines on the upper margin of the dactylus of the major cheliped, five (in both sexes) in the new species, 11 in A. grandis and 8–10 in A. pilocheira . The number of dactylar spines on the minor cheliped are similar in the three species, 8–9 in A. gathaagudu , 10–11 in the other two species. In A. gathaagudu the minor cheliped of the male is slightly more slender than in the female so any comparisons must be made between individuals of the same sex. The holotype of A. grandis from Taiwan is a female of carapace length 33.5 mm whose chelipeds were figured by Kensley and Chan (1998: fig. 4). The figured holotype of A. pilocheira is also a female of a similar size. The female major and minor chelipeds of A. gathaagudu are narrower (depth: dorsal length of propodus 0.85) and with more prominent marginal spines than in A. grandis (depth: dorsal length of propodus 1.25) whereas A. pilocheira is intermediate between them. Acanthaxius gathaagudu has narrower uropodal rami than the other species and, like A. pilocheira , has 8–9 marginal spines on the uropodal exopod compared to only five in A. grandis . Kensley and Chan (1998) remarked on the abdominal pleura, especially pleuron 5, which is posteriorly rectangular in A. grandis , rather than rounded as in A. pilocheira . We suspect that this may be a sexual difference–their figures of a paratype may be of a male whereas those of A. pilocheira are of female. The male of A. gathaagudu has a slightly more rectangular pleuron 5 than the female and a small spine on pleuron 6, absent in the female (cf. figs. 6a, 8a).

Figures

Figure 6. Acanthaxius gathaagudu sp. nov. a, lateral view. b, dorsal view of carapace, peduncles of antennule and antenna. c, telson and left uropod. d, sternites 7 and 8. e, left sternite 8 (lateral). f, left antenna peduncle (lateral). g, epistome, left antennule and antenna (ventral). h, maxilliped 3. i, major pereopod 1 (left, without setae, lateral). j, same (propodus, dactylus, without setae), mesial. k, same (propodus, without setae, lower). All figures from holotype.

Figure 7. Acanthaxius gathaagudu sp. nov. a, minor pereopod 1 (right, without setae, lateral). b, same (propodus, dactylus, without setae, mesial). c, same (propodus, lower). d–g, pereopods 2–5 (left except f). h, pereopod 5 fingers. i, j, female pleopods 1, 2. All figures from holotype.

Figure 8. Acanthaxius gathaagudu sp. nov. a, lateral view. b, dorsal view of carapace, peduncles of antennule and antenna. c, major pereopod (right, lateral, without setae). d, minor pereopod (left, lateral, without setae). e, male pleopod 2. All figures from paratype, NMV J55704.