Mursia microspina Davie & Short, 1989

Published, First, 2009, New records of crabs (Decapoda: Brachyura) from the New Zealand region, including a new species of Rochinia A. Milne-Edwards, 1875 (Majidae), and a revision of the genus Dromia Weber, 1795 (Dromiidae), Zootaxa 2111, pp. 1-66 : 36-40

Mursia microspina Davie & Short, 1989

( Figs 16a, b, 17a, b, 18a, b)

Mursia microspina Davie & Short, 1989: 172 , figs 9a–g, 10 [type locality: SE Queensland, Australia]. — Galil 1993: 365, figs 4e, 6h, i, 8e, f, 12 (colour). — Davie 2002: 128. — Takeda & Komatsu 2005: 277.

Mursia aspersa — Baba, Hayashi & Toriyama 1986: 221, pl. 165 [not Mursia aspersa Alcock, 1899 ].

Material Examined. Bay of Plenty: 1 female, 19.0 mm (with spines 20.8 mm) x 15.9 mm , 1 male, 30.8 mm (with spines 33.2 mm) x 26.8 mm, 37°28.14’S, 177°6.97’E – 37°28.11’S, 177°6.51’E, 230–318 m, Kaharoa, stn KAH9907/50, 5 June 1999 ( NIWA 48578 ) ; 1 female, 27.7 mm (with spines 32.6 mm) x 24.0 mm, 37°32.98’S, 176°58.44’E – 37°32.97’S, 176°58.63’E, 280– 155 m, Kaharoa, stn KAH0011/40, 5 Nov. 2000 ( NIWA 48581 ) .

Description. (only male characters unavailable for the type specimen and some additional female characters are given here): male abdominal somites 3–5 fused, but sutures still evident; somite 1 hidden beneath posterior margin of carapace; somite 2 with 3 large flattened, blunt transverse tubercles (“tri-lobate carina” of Galil, 1993); somite 3 with 2 low swellings on posterolateral corners; abdominal locking mechanism on somite 6 uses excavated posterolateral corners of to lock on to blunt tubercles on P2 sternite; telson triangular, longer than wide tip rounded. All somites of female abdomen free, margins setose; telson as in male; abdominal locking mechanism tubercles still present on P2 sternite of mature female. Gonopore simple, not operculate.

Cheliped superior margin in both sexes setose; outer face of propodus has 8 larger blunt tubercles adorning finely granulate surface, inferior margin of propodus with 12–14 small acute spines increasing in size distally; fingers down-curved, stout, tips crossed when closed; left cheliped fingers with 4, 5 interlocking teeth; right crusher cheliped fingers differ markedly, dactylus with large proximal molariform tooth fitting into proximal slot behind ridge on fixed finger and with 3, 4 distal teeth; margin of fixed finger divided into 2 parts, proximally there are 2 stout blunt teeth corresponding to molariform tooth on dactylus, while distal part has 3, 4 teeth increasing in size distally. Inner face of both male and female dactylus bears stridulatory ridge of about 25 fine transverse striae as is typical for Mursia . Row of about 20 small blunt tubercles lie along distal margin of third maxilliped ischium.

Walking legs (P2–P5) articles flattened, smooth, dactyli long, styliform, dorsal margin of meri setose. P2 longest, other pereopods decreasing in size posteriorly in both sexes.

Remarks. Davie & Short (1989) only had a male specimen that was missing its abdomen all the walking legs. The present collection includes intact specimens as well as females so it is now possible to complete the description of M. microspina . The male abdomen conforms to the generic pattern. Galil (1993) has already recorded several females from New Caledonia and the Loyalty Is, but she did not comment on the female characters. The female of M. microspina is typical of others in this genus.

Compared to the type specimen described by Davie & Short (1989) the present specimens show a few small differences: the seven rows of tubercles radiating out from the front in the type are less distinct, being more scattered than aligned; the rostrum is evenly rounded, rather than sculptured as in the type; the outer distal margin of cheliped merus has only two (rather than three) spines increasing in size, but there is a low proximal tubercle that may represent the first spine; the projections on the posterior carapace margin are more pronounced than as shown in Davie & Short (1989: fig. 9g). In other respects the New Zealand specimens agree closely with those from Australia. One feature that may be diagnostic of this species is the presence of a group of four blunt tubercles, forming the corners of an oblong, behind the orbits: the mesial pair is larger and further apart than the lateral pair. The supraorbital margins are eroded, allowing the eyes to view upwards, an appropriate adaptation for a sit-and-wait ambush predator that buries itself in the sand.

Galil (1993: fig. 12) provided a colour photo of a male from New Caledonia and described it as having “Branchial regions tinged red. Distal margin of buccal cavity [i.e. anterior face of epistome, just below antennules] with two red spots. Chelipeds pale coral, fingers white. Inner palmar face with a large oculusshaped coral-coloured patch.” The specimens from New Zealand show the same patterns except that the patch on the inner face of the palm is smaller and dark orange, rather than the dark red shown in her photo. The colour in the females is paler than that of the male.

Sound production in M. microspina involves a stridulatory ridge of around 25 fine transverse striae on the inner surface of the cheliped dactyli that a row of around 20 small rounded tubercles on the distal margin of the third maxilliped ischium rub against. These crabs normally hold their chelipeds close to their “face” as they lie semi-buried in sand, so sound production involves minimal movement of these appendages, thereby maintaining the cryptic position of the crab. This species can be compared with another sound producing crab that is part of the NZ fauna (see below). Ocypode pallidula has a similar row of striae on the inner face of the cheliped palm and to produce sound these are rubbed against a plectrum on a pair of closely spaced ridges on the ventral margin of the cheliped ischium. O. pallidula normally produces sound by vertical movements of the chelipeds while hiding in its burrow. In this species only one appendage is used to make the sound whereas in M. microspina both the chelipeds and third maxillipeds are employed. Sound is also produced by Ovalipes elongatus and O. catharus , but they employ different appendages (see O. elongatus below).

M. microspina is easily distinguished from M. australiensis by the short lateral carapace spines and the short meral spines on the chelipeds.

Distribution. Southeast Queensland, New Caledonia, Loyalty Is, and New Zealand. M. microspina lives on the continental shelf and continental slope. The New Zealand specimens came from samples taken between 155–318 m, but the exact upper limit of M. microspina in the shallowest sample is uncertain and could be anywhere from 155– 280 m. Depth range is 200– 420 m.