Plesionida aurelia, Ahyong, Shane T., Taylor, Joanne & Mccallum, Anna W., 2013

Ahyong, Shane T., Taylor, Joanne & Mccallum, Anna W., 2013, New species and new records of deepwater munidid squat lobsters from north-western Australia: Onconida, Bathymunida, Crosnierita, Plesionida and Torbenella, Zootaxa 3734 (1), pp. 23-37 : 32-35

Plesionida aurelia sp. nov.

( Figs. 1 D–E, 4)

Material examined. HOLOTYPE: NMV J62790 , ovigerous female (cl 9.0 mm, pcl 6.8 mm), off north-western Australia, Mermaid L24 north transect, 17°01.092–01.812'S, 119°35.460–34.998'E, 451– 440 m, beam trawl, SS05/ 2007/080 (acq. 015), 18 Jun 2007. PARATYPES: All from north-western Australia. NMV J56421 , 6 males (cl 6.6 mm, pcl 4.8 mm to cl 10.2 mm, pcl 7.8 mm), 4 ovigerous females (cl 7.7 mm, pcl 5.9 mm to cl 9.5 mm, pcl 7.4 mm), 5 females (cl 6.7 mm, pcl 5.0 mm to cl 9.2 mm, pcl 7.2 mm), same data as holotype; AM P90780, 1 male (cl 9.7 mm, pcl 7.5 mm), same data as holotype; NMV J56422 , 2 males (cl 8.5 mm, pcl 6.5 mm; cl 8.6 mm, pcl 6.8 mm), 1 ovigerous female (cl 8.9 mm, pcl 6.5 mm), 2 females (cl 8.8 mm, pcl 6.9 mm; cl 11.4 mm, pcl 9.0 mm), Broome L25 transect, 16°36.318–37.140'S, 120°34.476–34.020'E, 407–414 m, beam trawl, SS05/2007/120 (acq. 017), 30 Jun 2007; NMV J56114 , 2 females, smaller ovigerous (cl 7.8 mm, pcl 6.0 mm; cl 8.5 mm, pcl 6.6 mm), Imperieuse L23 transect, 17°27.612–27.912'S, 118°57.732–58.332'E, 412– 410 m, beam trawl, SS05/2007/055 (acq. 016), 15 Jun 2007; NMV J56115 , 1 ovigerous female (cl 8.9 mm, pcl 6.9 mm), Imperieuse L23 transect, 17°27.612–27.912'S, 118°57.732–58.332'E, 412– 410 m, beam trawl, SS05/2007/054 (acq. 017), 15 Jun 2007; NMV J56419 , 2 ovigerous females (cl 8.8 mm, pcl 6.9 mm; cl 9.9.mm, pcl 7.7 mm), 1 female (cl 10.9 mm, pcl 8.4 mm), Adele L28 transect, 14°03.750–03.702'S, 122°36.252–37.368'E, 397– 393 m, beam trawl, SS05/2007/167 (acq. 009), 4 Jul 2007; NMV J56423 , 1 male (cl 10.1 mm, pcl 7.9 mm), Mermaid L24 east transect, 17°03.438– 02.826'S, 119°40.014–39.708'E, 412–427 m, beam trawl, SS05/2007/076 (acq. 027), 15 Jun 2007; NMV J56425 , 1 female (cl 8.6 mm, pcl 6.6 mm), Kulumburu L29 transect, 13°15.900–16.350'S, 123°22.446–21.408'E, 394– 390 m, beam trawl, SS05/2007/180 (acq. 050), 6 Jul 2007.

Description. Carapace: Slightly wider than long (width 1.1 pcl). Rostrum well-developed, slender, apex blunt, not overreaching eyes; median carina straight, unarmed; with scattered granules lateral to median carina; supraocular spines short, blunt. Surface glabrous, with scattered tubercles and granules, forming oblique rows on branchial region; cervical groove distinct, deepest medially. Pair of prominent, sharp, epigastric spines behind supraorbital spines; large, sharp, laterally compressed, median gastric spine; prominent, sharp postcervical spine. Large, sharp, laterally compressed cardiac spine, similar size to median gastric spine. Dorsal orbital margins shallowly concave; lower orbital margins visible dorsally, mesially with short, subtriangular, distally rounded process. Anterolateral spine slender, straight, apex extending almost to level of apices of supraocular spines. Margins of carapace anterior to cervical groove irregularly dentate; with or without small spine at base of cervical groove; 4 sharp spines posterior to cervical groove; posterior ridge coarsely granular.

Sternum: Sternite 3 anteriorly sinuous; shallow median concavity; laterally subtruncate; posterior margin straight, medially contiguous with anterior margin of sternite 4. Sternite 4 broadly triangular, smooth, without striae. Sternites 5–7 smooth, without striae. Ridges demarcating sternites smooth.

Abdomen: Tergites 2–4 generally smooth; anterior margins granular, with pair of sharp, anteriorly directed submedian spines; distinct transverse groove behind submedian spines; pleura generally smooth. Tergites 5–6 unarmed. Telson subdivision distinct, with 12 plates.

Eye: Maximum corneal diameter 0.4 distance between apices of anterolateral spines; eyelashes absent; peduncle glabrous, smooth.

Antennule: Basal article elongated, not overreaching cornea; distomesial spine short; distolateral spine about quadruple length of distomesial spine; midlateral margin unarmed.

Antenna: Distomesial spine of basal article sharp, slender, reaching to midlength or apex of distolateral spine of basal antennular article. Article 2 almost twice length of article 3. Articles 2–4 unarmed. Flagellum shorter than pcl.

Maxilliped 3: Ischium with distinct distal flexor spine; extensor margin unarmed. Merus ovate, unarmed; length about 3 times width. Carpus unarmed. Crista dentata with row of 15 or 16 low, well spaced denticles.

Pereopod 1 (cheliped): Slender, 3.6–5.0 pcl (males), 3.2–3.7 pcl (females); appearing smooth but with scattered, short striae; sparsely setose. Dactylus mesial margin unarmed; occlusal margin finely denticulate, with gape and blunt proximal tooth in large males. Propodus palm 3.8–4.0 times as long as wide (males), 2.3–2.4 (females), longer than pollex; pollex margin unarmed. Carpus with short distal mesial spine; about 3.6–3.9 times as long as wide (males), 2.4–2.5 (females). Merus mesial margin with prominent, slightly compressed spine at distal end and at distal one-third; ventromesial surface with golden iridescent setae; small spine near carpal articulation. Ischium unarmed.

Pereopods 2–4: Compressed, similar, decreasing in length posteriorly; articles with sparsely distributed plumose and longer iridescent setae (meral extensor margins). Merus extensor margins unarmed, without distal spine; flexor margin unarmed except for triangular distal spine; length about 8 times as long as wide. Carpus unarmed, distal extensor angle with blunt tubercle or projection; with few striae and setae. Propodus slender, 9–10 times as long as wide, 0.6–0.8 times length of merus; extensor margin unarmed; flexor margin with 1–3 small movable spines (pereopod 2) or unarmed (pereopods 3–4) and 2 distal movable spines. Dactylus slender, 0.7–0.8 propodus length; flexor margin sinuous, smooth, unarmed; extensor margin crenulate proximally, with short, sinuous setae.

Pereopod 5: Dense setal brush on propodal flexor surface. Dactylus and proximal pollex setose, dactylus with small subdistal projection.

Egg diameter: 0.45–0.50 mm.

Etymology. Derived from aurelia, Latin for “golden”, alluding to the golden iridescent setae on the meri of the chelipeds and walking legs; used as a noun in apposition.

Colour in life ( Fig. 1 D–E). Overall translucent white with dark red spines, tubercles and ridges on carapace and abdominal somites 2–3; red crescent behind median gastric spine. Chelipeds translucent white with red segment articulations. Walking legs translucent white.

Remarks. Plesionida aurelia sp. nov. is the fourth known species of the genus, in addition to P. a l i e n a (Macpherson, 1996) ( New Caledonia), P. concava Cabezas, Macpherson & Machordom, 2009 ( Solomon Islands), and P. psila Baba & de Saint Laurent, 1996 ( New Caledonia). Plesionida aurelia sp. nov. is the first of the genus to be recorded from the Indian Ocean. The new species is most similar to P. psila , sharing pronounced median gastric, median cardiac and postcervical spines, features absent in P. a l i e n a and P. concava . The new species differs from P. psila in the much longer basal antennal spine, reaching anteriorly as far as the end, rather than the base, of the distolateral spine on the basal antennular article; in a more elongated maxilliped 3 merus, with length about 3 times, rather than twice the width; more slender walking legs, with meri and propodi about 8 and 9–10 times as long as wide, respectively versus about 6 and 8 in P. psila ; and in males, a small projection on the distomesial surface of the pereopod 5 dactylus. This last feature is notable as being previously found only in males of Onconida (Baba & de Saint Laurent 1996) (note that male pereopod 5 dactylus of Tasmanida Ahyong, 2007 , is not yet known).

Sexual dimorphism in P. aurelia is evident in the relative lengths of the chelipeds, being longest in males (3.6– 5.0 pcl in males versus 3.2–3.7 pcl in females). The largest males (pcl 9.7 mm or greater) also have a distinct tooth on the proximal occlusal margin. The degree of tuberculation on the carapace surface varies with size, being sparsest on the anterior half of the carapace in small specimens and reaching full development by about pcl 6.6 mm. The smallest ovigerous female measures pcl 6.0 mm.

Distribution. Presently known only from off north-western Australia; 393– 451 m.

Figures

FIGURE 1. A, Bathymunida balssi Van Dam, 1938, male, cl 5.0 mm, pcl 4.3 mm (NMV J 55274); B – C, Bathymunida dissimilis Baba & de Saint Laurent, 1996, male, cl 5.4 mm, pcl 4.7 mm; male, cl 4.7 mm, pcl 4.0 mm (NMV J 56002); D – E, Plesionida aurelia sp. nov., male paratype, cl 10.1 mm, pcl 7.9 mm (NMV J 56423), female paratype, cl. 8.9 mm, pcl 6.9 mm (NMV J 56115). Photos: K. Gowlett-Holmes.