Bioacoustics of Ocypode ceratophthalmus

Remarks . The morphology of the present specimens agrees well with the description and figures by Sakai & Türkay (2013) . The inner surface of the major palm has a stridulating ridge which consists of 30–49 elements (tubercles and striae) ( Fig. 2B ), and the G1 is three sided proximally and has a small thumb-shaped projection subdistally ( Fig. 2M–N ). There are variations in the number of stridulatory elements on the inner surface of the palm of the major cheliped (35–51) and minor chelipeds (0–10). These variations are related to size of the carapaces. Larger crabs have a larger number of stridulatory elements. On the inner surface of the palm of the minor cheliped, only specimens with more than 40.0 mm cw have this element ( Fadhillah et al., 2018 ). This species inhabits high intertidal areas with sandy substrate and is typically nocturnal. They are widely distributed in the Indonesian Archipelago; i.e., Sumatra Island, Java Island, Sulawesi Island, the Lesser Sunda Islands , the Moluccas , the Aru Islands , and Papua ( Rathbun, 1910 ; Tesch, 1918 ; Sakai & Türkay, 2013 ; Wada, 2019 ). The present study gives a new distribution record of the species in Indonesia .

Remarks. Ocypode ceratophthalmus (Pallas, 1772) as currently understood is a species complex, currently under study by P.J.F. Davie, H.-T. Shih and P.K.L. Ng, with three genetically distinct forms present in the Indian Ocean. Two are the commonly recognised white-and-maroon morphs and are morphologically close, but can be separated by details of the stridulatory apparatus on its chela. One white-maroon morph represents Ocypode ceratophthalmus sensu stricto , which occurs on islands as well as continental landmasses as well as in most of Southeast Asia and East Asia . The second white-maroon morph is known mostly from isolated islands and appears allied to O. pallidula Hombron & Jacquinot, 1846 . Whether it is a new species or there is older name now listed under its extensive synonymy will need to be established. The third morph is the most distinct, with a prominent green to greenishyellow coloration in life and a diagnostic stridulatory structure on its chela. This green morph is almost certainly a new species and is known only from islands in the Indian Ocean (see also Orchard 2012 ; Ma et al. 2018 ). All the material observed in the islands were of the green morph. The species was also observed on eight islands: viz; Agatti, Kavaratti, Amini, Chetlat, Androth, Bitra, Kilton and Kalpeni but specimens were not collected.

Remarks. Ocypode ceratophthalmus (Pallas, 1772) is a widespread Indo-West Pacific species of ghost crab, ranging from the eastern coast of Africa to the Hawaiian Islands and French Polynesia (Sakai & Türkay 2013). It is one of several species of Ocypode wherein the eyes have a distal corneous extension (stylus), although it can be distinguished from such congeners by the pattern of stridulatory ridges & tubercles on the inner surface of the palm of the major chela (viz. 10–11 interspaced tubercles in dorsal third, 8 thick striae in middle third, and 20–30 closely spaced striae in ventral third), the pointed fingertips of the minor chela, and the unique morphology of the G1 (Sakai & Türkay 2013: 679 (key), figs. 1D–I, 10, 32). In the Philippines , this species has been reported from several localities (see Table 1 ). The present material ( Fig. 5H ) from Manukan agrees well with the published descriptions of this species.