Charybdis (Goniohellenus) smithii MacLeay, 1838

Muñoz, Isabel, García-Isarch, Eva & Cuesta, Jose A., 2021, Annotated and updated checklist of marine crabs (Decapoda: Brachyura) of Mozambique supported by morphological and molecular data from shelf and slope species of the “ MOZAMBIQUE ” surveys, Zootaxa 5056 (1), pp. 1-67 : 45-46

Charybdis (Goniohellenus) smithii MacLeay, 1838

( Figures 14F , 16 )

Material examined. M08, Stn. 76, 222m, ♂ 64× 44.6mm (IEO-CD-MZ08/1794-1), 16S ( MZ 424974 ) , COI ( MZ 434822 ) ; ♂ 58× 40.7mm (IEO-CD-MZ08/1794-2), 16S ( MZ 424975 ) , COI ( MZ 434822 ) .

Habitat and distribution. Charybdis smithii is a semi-pelagic species that spends a considerable part of its life in the water column (Turkay & Spiridonov 2006), extending its pelagic habitat from the mixed layer to upper mesopelagic waters ( Romanov et al. 2009) at depths between 60 and 450m. It is distributed along the western and northern Indian Ocean, from off South Africa, Madagascar, Somalia, Seychelles, Maldives, Saya de Malha, Gulf of Aden, Red Sea, Bay of Bengal ( Apel & Spiridonov 1998; Turkey & Spiridonov 2006), although most of the crabs are found in the western basin of the Indian Ocean (Romanov et al. 2008). C. smithii is common in the pelagic provinces of the western Indian Ocean, where they are driven to, by the wind monsoon regime. Based on the nutritive value determined for this species, Kumar et al. (2019) raised the possibility of its potential exploitation as a commercial resource.

Results and remarks. These two male specimens agree well with the descriptions and figures in Apel & Spiridonov (1998) and Turkey & Spiridonov (2006). They were collected during the 2008 survey at 222m depth. This is the first record of C. smithii off Mozambique. Ng & Takeda (1999) reported that two closely allied species, C. smithii and Charybdis omanensis , differ in many morphometric and gonopodal characters. Türkay & Spiridonov (2006) reviewed the deep-water species belonging to Charybdis subgenus Goniohellenus , and described a new subspecies, C. (G.) omanensis septentrionalis Türkay & Spiridonov, 2006 restricted to the central and southern Red Sea and further extended to the Arabian Sea and India (Josileen et al. 2018). The diagnostic characters used for the identification of our specimens as C. smithii instead the subspecies C. omanensis septentrionalis , based on Türkay & Spiridonov (2006) are: posterolateral angles of the carapace nearly rounded instead almost forming a right-angle, as described for C. omanensis septentrionalis (see Figure 16A ); the carapace not densely pilose and without the frontal patches of granules neither protogastrics areas with short bands of three–four lines of granules described for C. omanensis septentrionalis ; tips of G1 of the two males are not twisted downwards as they are for C. omanensis septentrionalis ( Apel & Spiridonov 1998) (see Figures 16B,C ).

Colouration observed. Both male specimens were reddish, with smooth carapace without granular patches, as described by Turkay & Spiridonov (2006). The tubercles on the chelipeds were dark red. Some irregular white spots were bordering the upper zone of the epibranchial region, with the shape of a semicircle. This colour pattern was not described by Apel & Spiridonov (1998) or Turkey & Spiridonov (2006). The finger tips were deep brown. After preservation in ethanol, the specimens turned to beige with some pinkish patches, the finger tips remaining brown.

DNA barcodes. The 16S and the COI sequences of the two specimens present the same haplotypes that fits 100% with the 16S and COI sequences of C. smithii ( KX 060404 , KX060191 ) from the same specimen (MNHB27685) from Oman ( Negri et al. 2018). However, also de COI sequences fit 100% with the three sequences of C. omanensis septentrionalis ( KY 651228 - KY651230 ) uploaded to Genbank by Josileen et al. (unpublished).

Figures

FIGURE 14. A, Chaceon macphersoni, ♀ IEO-CD-MZ09/1812; B, Ovalipes iridescens, ♀ IEO-CD-MZ07/1921. C, Scylla serrata, ♀ IEO-CD-MZ08/2238 (preserved); D, Charybdis africana, ♂ IEO-CD-MZ08/1813; E, Charybdis feriata, ♂ IEO-CD- MZ07/1902 (preserved); F, Charybdis smithii, ♂ IEO-CD-MZ08/1813; G, Monodaeus tuberculidens, ♂ IEO-CD-MZ07/1803. Scale bars: 1cm.

FIGURE 16. Charybdis smithii ♂, IEO-CD-MZ08/1794-1. A, Carapace (Scale bar: 1cm); B,C, G1 (Scale bars: 1mm).