Gastroptychus brachyterus Baba, 2005

Mccallum, Anna W. & Poore, Gary C. B., 2013, Chirostylidae of Australia’s western continental margin (Crustacea: Decapoda: Anomura), with the description of five new species, Zootaxa 3664 (2), pp. 149-175 : 150-152

Gastroptychus brachyterus Baba, 2005

( Fig. 11 B)

Gastroptychus brachyterus Baba, 2005: 20 , figs 3b, 4, 213 (key, synonymies)

Material examined. Two ovigerous females (cl 10.9, 12.1 mm), 2 males (cl 10.7, 12.5 mm) Western Australia (13°15.9'S, 123°22.45'E – 13°16.35'S, 123°21.4'E), 390–394 m, 0 7 Jul 2007 (stn SS05/2007 180), CSIRO acquisition number 0 40, NMV J56001 .

Colour. Body and appendages pale orange.

Distribution. Kei Islands, Indonesia, and north-western Australia, 345– 390 m.

Remarks. This material agrees well with the description provided by Baba (2005). This is the first record of this species for Australia. Ovigerous females carry 8– 12 eggs (ovum 1.7 mm).

Gastroptychus investigatoris (Alcock & Anderson, 1899) ( Fig. 1 , 11A )

Ptychogaster investigatoris Alcock & Anderson, 1899: 24 .

Chirostylus investigatoris .—Doflein & Balss, 1913: 132, figs 1, 2. Gastroptychus investigatoris .—Zarenkov & Khodkina, 1981: 86, fig. 3.

Material examined. Two females (cl 20.0, 16.7 mm), 3 males (cl 12.1, 14.0, 17.1 mm), Western Australia (13°15.9'S, 123°22.45'E – 13°16.35'S, 123°21.4'E), 390–394 m, 0 7 Jul 2007 (stn SS05/2007 180), CSIRO acquisition number 0 38, NMV J56000 .

Diagnosis. Carapace excluding rostrum as long as wide; with prominent spines and few interspersed ones; gastric region with prominent spines in hexagonal arrangement with central spine; midcervical groove at about midlength of carapace. Rostrum spinose, 0.4 times remaining carapace length. Anterior margin of sternite 3 elevated, with median ridge anteriorly produced. Abdomen thickly covered with fine setae and partly covered in spines, spines absent from somite 3. Antennal scale rudimentary. Maxillipeds 3 close together.

Description. Carapace: Carapace excluding rostrum as long as wide; width between anterolateral margins 0.5 times that of broadest carapace width; lateral margins of branchial region convex with posterolateral margin somewhat excavated; dorsal surface covered with many large thorn-shaped forward pointing spines and smaller intermediate spines; 2 large submarginal hepatic spines; gastric region with prominent spine in centre of hexagonally arranged large spines; 3 pairs of large spines in midline posterior to cervical groove; branchial region with approximately 7 moderate spines amongst many smaller spines and a row of 10 small submarginal spines; surface without setae. Pterygostomian region with 4 anteriorly submarginal spines and approximately 3 rows of spines. Rostrum spinose, straight and sharply upturned; 0.4 times remaining carapace length.

Sternum: Sternite 3 with median ridge anteriorly produced and elevated. Sternite 4 with 2 pairs of large spines along anterior border, 3 pairs of large spines along the midline, and a scattering of small spines. Sternite 5 with 2– 3 small spines on lateral margins and a row of tubercle-like spines on anterior margin.

Abdomen: Abdominal Somite 1 with transverse row of 14 large stout spines. Somite 2 with median process composed of large paired conical spines separated by 2 pairs of smaller spines, laterally with a pair of large low conical spines, which sometimes possess an accessory spine. Somite 3 with low transverse ridge anteriorly and pair of low processes laterally. Somite 4 with lateral pair of large conical spines directed posteriorly and sometimes with a smaller spine anterolaterally. Somites 5 and 6 with many large spines.

Eyes: Cornea subglobular, distinctly wider than peduncle, reaching anteriorly to midlength of rostrum.

Antennule: Article 1 unarmed, bearing short fine setae on margin.

Antenna: Article 4 without distal spine; article 5 with acute distolateral spine, twice as long as article 4. Antennal scale rudimentary.

Maxilliped 3: Close together; basis with large spine; ischium with 17 spines on mesial ridge; merus with small distolateral spine; carpus with well developed distolateral spine; propodus unarmed; dactylus with 2 rows of approximately 13 corneous spines.

Pereopod 1 (cheliped): Subcylindrical, 6 times carapace length, sparingly setose, with longitudinal rows of close-set spines; propodus 3.4 times dactylus length; occlusal margins dentate and setose.

Pereopods 2–4: Similar, about 4 times carapace length; sparsely setose. Basis spinose; ischium, carpus, merus and propodus with longitudinal rows of close-set spines; propodus with flexor margins lined with 14–17 movable slender spines; dactylus about 0.3 propodus length, with 10 movable slender spines on flexor margin, extensor margin with clusters of setae and proximal row of short plumose setae.

Colour. Body and appendages orange.

Distribution. Marcus-Necker Rise, the Philippines, Andaman Sea, south-west India, Sumatra, the Maldives and north-western Australia, 390–1463 m.

Remarks. Despite being relatively widespread, few specimens of this species have been collected. Until now the most complete illustrations were those from very early publications (Alcock & Anderson 1899b; Alcock & McArdle 1902), with some additional illustrations of the antenna, and sternite 4 by Baba (1988). The north-western Australian specimens appear to have more spines on the gastric region and the surface of sternite 4 than shown in the original description and illustrations of the sternite in Baba (1988). This is the first record of the species in Australia.

Figures

FIGURE 1. Gastroptychus investigatoris (Alcock & Anderson, 1899), female (20.0 mm), NMV J 56000. A, carapace and abdomen, dorsal. B, carapace and abdomen, lateral. C, sternum. D. telson and abdominal segments 5 and 6. E, right antenna and antennule, ventral. F, maxilliped 3, right, lateral. G, pereopod 1, left, distal part. H, pereopod 2, left, distal part. Scales: A – D, H & G = 5 mm, E & F = 1 mm.

FIGURE 11. A, Gastroptychus investigatoris (Alcock & Anderson, 1899), NMV J 56000. B, Gastroptychus brachyterus Baba, 2005, NMV J 56001. C, Uroptychodes grandirostris (Yokoya, 1933), NMV J 56125.