Cycloachelous granulatus (H. Milne Edwards, 1834 )

Shaga, I Bevin, Priya, K, Ramar, Selvakumar, Srinidhi, S, Mohan, G Chandra, Ranganathan, Sukanya, Moulvi, S M M & Mani, Bhuvaneswari, 2023, A Small Collection of Subtidal Crabs (Crustacea: Decapoda: Brachyura) from the Palau Islands Collected by Dredging, Bulletin of the National Museum of Nature and Science. Series A, Zoology 49 (1), pp. 7-42 : 18-19

Cycloachelous granulatus (H. Milne Edwards, 1834)

Material examined. Kayangel Atoll., north of Babelthuap I., Palau Is., lagoon, dredged, 4 m in depth; 1 ♂ (cb 4.8×cl 3.9 mm), NSMT-Cr 30967; July 6, 1980; K. Baba leg. ─ Entrance of Toagel Mid in Arangel Channel, Babelthuap I., Palau Is., dredged, 40 m in depth, mud; 1 ♀ (10.1× 7.9 mm), NSMT-Cr 30968; June 22, 1980; K. Baba leg.

Remarks. There are many records of this species from the whole Indo-West Pacific, with some generic and subgeneric names such as Lupea by H. Milne Edwards (1834), Achelous by A. Milne-Edwards (1861), Portunus (Achelous) by Rathbun (1911), Neptunus (Achelous) by

Alcock (1899), Gordon (1938), and Sakai (1939), Cycloachelous by Ward (1942), Portunus by Stephenson and Campbell (1959), Crosnier (1962), Sakai (1965), Dai and Yang (1991), and Apel and Spiridonov (1998), and Portunus (Cycloachelous) by Sakai (1976). These records are, however, not always reliable, with certain anxiety about the confusion with two closely related species, Cycloachlous orbitosinus ( Rathbun, 1911) and C. levigatus Koch, 2021 , and also with another species, C. octodentatus (Gordon, 1918) .

Koch (2021) made the detailed comparison of the new species, C. levigatus , with C. orbitosinus and C. octodentatus . Then, Koch et al. (2022) further discussed the systematic status of the genus based on the morphological and molecular analyses and showed the presence of nine congeneric species. These three species are also similar to C. granulatus (H. Milne Edwards, 1834) in the shape, dorsal areolation and anterolateral armature of the carapace.

Apel and Spiridonov (1998) used the characters to distinguish C. granulatus from C. orbitosinus in the key that ʺLast anterolateral tooth not larger than other teeth; carapace granules are not grouped in patches but almost cover entire surface; under side of manus without longitudinal furrow along most of its length; lateral borders of second abdominal segment in both sexes without dorsally directed spiniform process; Go/1 short and stout with flared tip.ʺ

The pleons of both sexes of C. orbitosinus and C. levigatus , and the male pleon of C. octodentatus were clearly shown by Koch (2021), and the male pleon of C. granulatus by Koch et al. (2022). The lateral margins of the sixth pleonite are straight or weakly curved in C. granulatus , whereas strongly convex in C. orbitosinus and C. levigatus , and rather angulated in C. octodentatus . Furthermore, the additional definitive difference is that the pleonal surfaces of both sexes are characteristically sculptured in C. oribitosinus and smooth in the other three species. Considering these distinguishing characters, the male and female specimens examined, though young, are safely referred to C. granulatus .

Distribution. The type locality of C. levigatus is Nhatrang Bay, Vietnam, and the other localities in the literature confirmed by the original author are the Philippines ( Stephenson and Rees, 1967, as Portunus orbitosinus ) and Japan ( Sakai, 1939, as Neptunus (Achelous) orbitospinis; 1965, as P. orbitospinus ; 1976, as P. (Cycloachelous) orbitosinus ). The following conclusive comments on the distribution were recorded by the original author; C. levigatus localities are in East or Southeast Asian waters, in comparison with C. orbitosinus from the western Indian Ocean.

The type locality of C. octodentatus is Singapore, while the present species is widely distributed in the whole Indo-West Pacific at the depth of 30 to 120 m.