Charybdis (Charybdis) rosaea (Hombron and Jacquinot, 1846)

Manikandan, K, Megalaa, N, Valliappan, Subramanian, Nandini, K, Rani, Lourdu V, Dakshinamurthi, Senthil & Nagappan, Nagappan, 2022, Crabs (Crustacea, Decapoda) from the Seas of East and Southeast Asia Collected by the RV Hakuhō Maru (KH- 72 - 1 Cruise) 3. Sahul Shelf, Bulletin of the National Museum of Nature and Science. Series A, Zoology 48 (2), pp. 35-83 : 62-63

Charybdis (Charybdis) rosaea (Hombron and Jacquinot, 1846)

( Fig. 12)

Material examined. RV Hakuhō Maru KH-72-1 cruise, sta. 32, 1 Ə( CB 32.4 mm including lateral spines×CL 26.6 mm in median line), NSMT-Cr 30774, 1 Ə(34.8× 27.9 mm), NSMT-Cr 30775; 1 Ə(34.8× 27.7 mm), NSMT- Cr 30776; 13ƏƏ (29.6×23.0 mm – 35.0× 26.6 mm), 8 $$ (29.3× 22.2 mm – 34.6× 26.2 mm), 2 young $$ (27.3× 21.1 mm, 28.7× 21.8 mm), NSMT-Cr 30730.

Remarks. The present specimens identified as Charybdis (Charybdis) rosaea (Hombron and Jacquinot, 1846) agree with the elaborate figures given by Leene (1938: fig. 14; 1940: pl. 5), and with a fine photograph presented by Moosa (1995: fig. 10c). In all the specimens examined, the carapace ( Fig. 12A, C) is much narrower than the typical species of Charybdis , with the short sixth (last) anterolateral tooth of the carapace; the carapace dorsal surface is wholly covered with fine tomentum; the carapace regions are indicated by nude, narrow banded and depressed swellings, with the mesogastric swellings of both sides united medially and laterally with each protogastric swelling; the meso- and metagastric swellings are united by a longitudinal swelling along the median line; six frontal teeth are in three pairs, the median two teeth being the most strongly developed and triangular in dorsal view, each with sharp or somewhat obtuse apex, each submedian tooth is subtruncated and oblique along the inner margin and longitudinal along the outer margin, each lateral tooth is about half as wide as the submedian tooth and separated from the submedian tooth by a deep incision.

Leene`s (1940) figure and Moosa`s (1995) photograph are quite effective in showing all the characters mentioned above as for this very rare species. The carapace dorsal areolation is, however, somewhat similar to some specimens of C. (C.) callianassa (Herbst, 1789) mentioned by Stephenson et al. (1957). According to them, in C. (C.) callianassa , the length/breadth ratio of the carapace varies, owing to increasing length of the last anterolateral tooth with increasing size of specimen; extremes are given by Stephenson et al. (1957: fig. 1C–D). Of the two figures, fig. 1D is just that mentioned above, its contour being quite similar to that of Leene`s figure in question. In some published figures of C. callianassa , the epibranchial teeth of both sides are protruded sharply, making the carapace appearance wider, but in the illustration given by Wee and Ng (1995: fig. 8A), in which the carapace is moder- ately wide, the meso- and metagastric lines are connected by a median longitudinal line. The large specimens having the narrow carapace identified as C. callianassa should be re-exam- ined for the definite identification.

The present specimens were collected by a long-handled scoop net from swarms in the surface layer at night during a full moon. The details of the swarming were not recorded, but similar swarming behavior is rather well known in the Indian Ocean species Charybdis (Archias) smithii MacLeay, 1838 , taxonomically studied by Ng and Takeda (1999). Charybdis (A.) smithii has been ecologically studied by Zamarov et al. (1991), Van Couwelaar et al. (1997), and Apel and Spiridonov (1998), and also by earlier workers under the name of C. (Goniohellenus) edwardsi Leene and Buitendijk, 1949 , by Della Croce and Holthuis (1965), and Daniel and Chakrapany (1984). According to Moosa (1995), the specimens identified as C. (C.) rosaea from Indonesia have been caught during hauls in 350 to 676– 699 m depth, but they were probably caught while the trawl was being brought up to the surface.

Distribution. Known from off New Guinea (type locality), and the Kai Islands and Tanimbar Islands, Indonesia, and now from the Sahul Shelf, Australia.