Ocypode pallidula Jacquinot

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 : 53-57

Ocypode pallidula Jacquinot , in Hombron & Jacquinot, 1846

Figs 27a, b, 28a, b, 29a, b.

Ocypode pallidula Jacquinot , in Hombron & Jacquinot, 1846: pl. 6, fig. 1 — Sakai & Turkay 1976: 87, figs 14, 15. — Jones 1988: 36 ( Table 1). — Takeda & Webber 2006: 223, fig. 17A–C. — Davie 2002: 358.

Ocypode laevis Dana, 1852: 325 : 1855: 325, pl. 20, fig. 2.

Ocypode cordimana — Jacquinot & Lucas 1853: 65. [Not Ocypode cordimanus Latreille, 1818 .]

Ocypoda kuhlii — Chilton 1911: 561. [Not Ocypode kuhlii De Haan, 1835 .]

Material Examined. Kermadec Is: AQ2422, 1 female, 22.3 mm x 20.6 mm, coll. W. R. B. Oliver, 1908, Canterbury Museum (reported by Chilton, 1911); AQ2376, 1 juv., 6.5 mm x 5.3 mm, 1 female, 7.3 mm x 6.2 mm, 1 male, 9.6 mm x 8.4 mm, coll. J.H. Sorensen, sandy beach, Raoul I., 2 May 1944 . Oneraki Beach , Raoul I.: 2 males, 19.0 mm x 16.4 mm, 19.4 mm x 16.7 mm, coll. by Marion Rhodes, 18 Apr. 2003 ; 1 female, 18.4 mm x 15.8 mm, coll. by Erica Cammack, 20 June 2003; 1 male, 20.5 mm x 18.6 mm, 1 female, 22.5 mm x 20.3 mm, coll. Kala Sivaguru, DOC, 7 Aug. 2007.

Norfolk I.: AQ2420, 2 males, 23.1 mm x 20.3 mm, 24.1 mm x 20.8 mm, 29° 00ʹS, 168° 00ʹE, coll. by W. R. B. Oliver, 1913 .

New Zealand: 1 male, 19.4 mm x 17.4 mm, Pakiri Beach, Leigh Marine Reserve , Auckland, 36° 17ʹS, 174° 48ʹE, 11 May 2001 .

Remarks. Ghost crabs are usually found in intertidal burrows on sandy beaches. The main features used to identify the species of Ocypode are the presence/absence of ocular stylets, presence/absence of “brushes of hairs” on the walking legs and the number, shape and arrangement of striae on the stridulatory crest found on the inside of the major cheliped palm. Chilton (1911) reported Ocypoda kuhlii De Haan from “Sunday I.” and “Thursday I.” (old names for islands in the Kermadec Group). These specimens, deposited in the Canterbury Museum, have been re-examined and found to be Ocypode pallidula and they agree very well with ghost crabs of the same species reported by Takeda & Webber (2006). The stridulatory ridge of O. kuhlii is made up of 7–17 round or ovoid tubercles whereas in O. pallidula there are 25–40 evenly spaced fine striae ( Jones, 1988). The number of striae on the chelipeds of the material examined here was 20–25 for males (mean = 23) and 15–19 for females (mean = 17). Sexual dimorphism of the stridulatory ridge has not been reported before, but it is probably the result of positive allometry of the male cheliped. Takeda & Webber (2006) figure the stridulatory ridge of O. pallidula (their Fig. 17A) which has around 22 evenly spaced striae on the inside of the propodus. The range in number of striae given by Jones (1988) for O. pallidula , needs to be revised from, 25–40 to 15–40, so as to accommodate females. The number of striae is still one of the best characters to use, along with a few others, to identify ghost crabs.

The majority (7/11) of crabs reported here have the major cheliped on the left instead of the right hand side. Sound is produced underground in the burrow (Hicks etal, 1984) by vertical movements of the palm rubbing the stridulatory ridge against the plectrum, which is a pair of closely spaced ridges on the ventral margin of the cheliped ischium. Whether on the left or on the right, the minor cheliped never had any striae on the inner surface of the propodus. Immature crabs lack a stridulatory ridge.

There is only one species of ghost crab on the Kermadec Is and O. kuhlii should be omitted from the checklist compiled by Takeda & Webber (2006). Besides O. pallidula , five other species of Ocypode are known from mainland Australia ( Davie, 2002).

The discovery of one adult male specimen of O. pallidula on the beach at Leigh Marine Reserve is the first reliable record of a ghost crab from the New Zealand mainland. Two explanations seem possible: either it is a natural occurrence resulting from recruitment of larvae produced at perhaps Norfolk I. or the Kermadec Is or it is an escapee from a diver’s bag left on the beach. The single record of a mature-sized crab found in a burrow on the beach suggests that it may well be an escapee, which implies that the animal survived transport to New Zealand in amongst diving gear. Since ghost crabs are semi-terrestrial it is not impossible that it could have survived several days inside a damp bag. If the occurrence was natural we would have expected to find several crabs in burrows on the beach. Given that level of foot traffic along the beach and the nearby marine laboratory, it seems likely that someone would have noticed more burrows if they were there, so the one-off event suggests that there has been a breach of biosecurity and the crab has escaped while the owner was off diving in the marine reserve. A natural recruit to the beach would have had to have been there for perhaps a year before reaching adulthood and would have created many burrows during that time. Subsequent searches after the initial discovery have not revealed the presence of any more crabs. Perhaps Biosecurity staff should pay more attention to dive bags and their contents brought into New Zealand by passengers. Given the very wide distribution of O. pallidula (see below) it is difficult to say exactly where the interloper may have come from. The nearest sources frequented by divers would be Norfolk I., Cook Is and Queensland, Australia.

Distribution. Madagascar, Mauritius, Moluccas, Timor, Celebes, New Guinea, Australia (Queensland, Coral Sea), Norfolk I., Kermadec Is, Cook Is, French Polynesia (type locality: Gambier Is, Tuamotu Archipelago), Johnston I, Laysan I and Midway. It is clearly a widespread Indo-West Pacific species. Ocypode pallidula inhabits the intertidal zone on sandy shores.

Brachyuran Fauna of the Kermadec Is The first compilation of the crab fauna of the Kermadec Is, north of mainland New Zealand, was done by Chilton (1911) who listed 25 species. Almost 100 years was to pass before this number was revised: Takeda & Webber (2006) were able to list 57 species, including 5 that were new. Seven additional species, 4 Leucosiidae , 2 Parthenopidae and 1 Xanthidae , await future publication, so that altogether the fauna could include 64 species.

However Takeda & Webber did not view all the species in their list and relied upon identifications made by Chilton (1911) for some records. I have examined Chilton’s specimens, held by the Canterbury Museum, and I am able to correct the list that he produced and thus the list provided by Takeda & Webber (2006). Three species should be omitted: “ Ovalipes bipustulatus ” as used by Chilton in that context refers to O. elongatus , and similarly, Percnon affine refers to P. planissimum , and Ocypode kuhlii refers to O. pallidula .

McLay (2007) recorded 2 new families associated with hydro-thermal vents near the Kermadecs, represented by Gandalfus puia McLay, 2007 ( Bythograeidae Williams, 1980 ) and Xenograpsus ngatama McLay, 2007 ( Xenograpsidae Ng, Davie, Schubart & Ng, 2007 ). From the same collections Ng & McLay (2007) discovered 2 new species, Euryxanthops chiltoni Ng & McLay, 2007 ( Xanthidae Macleay, 1838 ) and Medaeops serenei Ng & McLay, 2007 ( Xanthidae Macleay, 1838 ) from the Macauley Caldera north of the Kermadec Is.

In the present paper one new species, Rochina ahyongi sp. nov. is described from the Rumble Seamount near the Kermadec Is and Thalamita danae is added to the Kermadec fauna. Not all of Chilton’s collection in the Canterbury Museum has been identified to species and so several new records and/or species will be added. Thus at the moment the number of species known from the Kermadec Is area sits at 67.