Planaxius brevifrons Komai and Tachikawa, 2008

Poore, Gary C. B. & Collins, David J., 2009, Australian Axiidae (Crustacea: Decapoda: Axiidea), Memoirs of Museum Victoria 66 (2), pp. 221-287 : 272

Planaxius brevifrons Komai and Tachikawa, 2008

Planaxius brevifrons Komai and Tachikawa, 2008: 24–29 , figs. 2–6.

Figures 34 , 46

Material examined. WA, off Jurien Bay , 29°48.33'S, 114°25.52'E – 29°48.33'S, 114°25.55'E (stn SS10-2005 083), 113–114 m, 02 Dec 2005, NMV J55445 (male, cl. 3.3 mm, tl. 9.5 mm, without pereopods 3–5) .

Description of male. Carapace smooth, cervical groove short. Rostrum 0.3 times length of front-to-cervical groove, triangular, with 2 or 3 short oblique lateral spines anterior to supraocular spine, continuous with definite lateral gastric carinae. Supraocular spines prominent. Lateral gastric carina unarmed. Submedian gastric carina absent. Median gastric carina low, sharp, unarmed. Branchiostegal angle produced, lobe-like, with 2 minute marginal teeth. Sternite 8 (pereopod 5) with setal ridge on anterior face at base of leg. Abdominal pleuron 1, 3 times as deep as middorsal length, ventrally acute; pleuron 2 broad, lateral length 1.8 times dorsal length, anteroventrally rounded; pleura 3–5 becoming more posteroventrally square, each with anteroventral tooth; pleuron 6 with small tooth on ventral margin.

Eyestalk 0.5 length of rostrum; cornea pigmented. Antennular peduncle reaching to proximal part of antennal article 5. Antennal article 1 with 2 spinules on lower distal margin; article 2 distal spine slender, directed slightly inwards, reaching distally one third of antennal article 4; scaphocerite slender, straight, reaching distally two-thirds of article 4; article 3 with 1 spine on mesial lower margin; article 4 about 1.3 times length of article 2 (excluding distal spine), article 5 about one-third length of article 4. Maxilliped 3 basis with 1 spine; ischium with 3 spines on lower margin; crista dentata with 13 teeth; merus with 4 spines on lower margin; carpus with 1 spine.

Pereopods 1 asymmetrical, propodus of major longer, more swollen. Major pereopod 1 (right) coxa lower margin with 1 spine; basis lower margin unarmed; ischium lower margin with 3 spines; merus upper margin convex, with 2 spines, lower margin with 6 spines, lateral face smooth, mesial face smooth; carpus unarmed, smooth; propodus upper margin carinate, with small distal spine, lower margin smooth, lateral face smooth, mesial face smooth; fixed finger half length of upper palm, cutting edge unevenly denticulate; dactylus smooth, cutting edge as in fixed finger.

Minor pereopod 1 coxa as in larger cheliped; ischium lower margin with 1 spine; merus upper margin convex, with 2 spines, lower margin with 6 spines, lateral face smooth, mesial face smooth; carpus unarmed, smooth; propodus upper margin carinate, with small distal spine, lower margin smooth, lateral face smooth, mesial face smooth; fixed finger as long as upper palm, cutting edge unevenly denticulate; dactylus smooth, cutting edge scarcely denticulate.

Pereopod 2 ischium lower margin unarmed; merus lower margin unarmed; carpus as long as chela; propodus upper margin 0.8 length of dactylus. Pereopods 3–5 missing.

Pleopod 1 of 2 fused articles; article 2 blade-like, apex unevely bilobed, appendix interna represented by few hooks. Pleopod 2 with appendix masculina as long as remaining endpod; appendix interna third length of endopod, 0.6 length of appendix masculina. Pleopods 2–5 appendix interna one third length of endopod.

Telson 1.5 times as long as wide, lateral margin with 3 spines, distal margin convex without posteromedian spine, posterolateral angle with 2 robust setae, one much larger; dorsal face with 2 small spines in each oblique row. Uropodal endopod 1.8 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 4 lateral spines, 2 longitudinal ribs (outer rib with 2 spines), posterolateral angle with 1 fixed spine and 1 robust seta; transverse suture with 4 spines.

Distribution. Japan, Kii Peninsula, Ogasawara Is, 47–100 m; WA, south-western coast, 114 m depth.

Remarks. The single male is virtually indistinguisable from slightly larger specimens reported from Japan by Komai and Tachikawa (2008). Dr Komai kindly re-examined the type material at our request and confirmed the presence of a median gastric carina, more clear and sharp in the paratypes than in the illustrated holotype, as in the WA specimen. While the ischium of maxilliped 3 of the Australian specimen has blunt teeth along the lower margin some of the Japanese specimens have one or two minute spinules obscured by stiff setae. Dr Komai confirmed that the two minute teeth on the anterior branchiostegal lobe of the Australian specimen are absent in the Japanese material. The uropodal endopod of the holotype lacks the lateral and distolateral spines seen in the Australian specimen. While we have only one specimen, none of these differences argues strongly for a separate species but the record is a considerable range extension.

Figures

Figure 34. Planaxius brevifrons Komai and Tachikawa, 2008. a, lateral view. b, dorsal view of carapace, peduncles of antennule and antenna. c, telson and right uropod. d, sternites 7 and 8, pleonite 1 with left pleopod 1 in situ. e, sternites 7 and 8, pleonite 1 with left pleopod 1 in situ (lateral). f, epistome, right antennule and antenna (ventral). g, maxilliped 3. h, major pereopod 1 (right, lateral). i, minor pereopod 1 (left). j, pereopod 2. k, l, male pleopods 1, 2. All figures from NMV J55445.

Figure 46. Planaxius brevifrons Komai and Tachikawa, 2008. Photomicrographs of (left to right) maxilla 1, maxilla 2 (posterior epipod seta truncated), maxilliped 1, maxilliped 2.