Sesarma rectum Randall, 1840

Ng, Peter K. L. & Schubart, Christoph D., 2003, On the identities of Sesarma obesum Dana, 1851, and Sesarma eydouxi H. Milne Edwards, 1853 (Crustacea, Decapoda, Brachyura, Sesarmidae), Zoosystema 25 (3), pp. 425-437 : 430-435

Sesarma rectum Randall, 1840

( Figs 4-7)

Sesarma recta Randall, 1840: 123 .

Sesarma eydouxi H. Milne Edwards, 1853: 184 . — Heller 1865: 64. — de Man 1880: 23; 1887: 643; 1892: 248.

Sesarma müllerii A. Milne Edwards, 1869: 29 .

Sesarma (Holometopus) recta – Tesch 1917: 190.

Sesarma (Holometopus) eydouxi – Tesch 1917: 150, figs 3, 4. — Serène 1968: 107.

Sesarma (Holometopus) rectum – Rathbun 1918: 298, pl. 82. — Holthuis 1959: 243, fig. 61, pl. 11, fig. 4. — Chace & Hobbs 1969: 182, fig. 62j.

Sesarma (Sesarma) rectum – von Hagen 1978: 45, figs 1a, 2a, 3a, 4a, 5a.

Sesarma rectum – von Hagen 1975: 301, fig. 7. — Abele 1992: 15, figs 3b, 4b, 5d, 9. — Schubart et al. 1999: 537.

Chiromantes eydouxi – Ng & Liu 1999: 229.

MATERIAL EXAMINED. — Surinam. Coll. Hering, 1 32.8 × 26.7 mm, holotype of Sesarma recta Randall, 1840 ( ANSP 3976). — Coquette collections, 12.V.1957, coll. L. B. Holthuis, 1 ( USNM 103276).

“Cochin-China”. 1 31.2 × 27.2 mm, lectotype of Sesarma eydouxi H. Milne Edwards, 1853 ( MNHN B10930).

Grenada. Fort Jeudy, 15.VIII.1994, coll. R. Diesel, D. Horst, C. Schubart, 1 21.1 × 18.4 mm, 2 18.0 × 15.5, 16.8 × 14.5 mm ( SMF 23248), 1 16.5 × 14.3 mm ( SMF 23249).

Brazil. Rio Grande do Norte, 1 29.9 × 26.8 mm ( MCZ 6230). — Rio Paraiba do Norte, 3 26.4 × 22.9 mm, 17.7 × 15.1 mm, 11.7 × 9.8 mm, 1 21.1 × 17.9 mm ( MCZ 6231). — Pernambuco, 3 juvenile 14.4 × 12.5 mm, 8.0 × 7.0 mm, 7.4 × 6.4 mm, 1 22.8 × 19.1 mm ( MCZ 6232). — Sta Clara, 2 30.8 × 27.5 mm, 23.2 × 20.2 mm, 2 29.4 × 26.1 mm, 27.8 × 24.4 mm ( MCZ 6233). — Rio de Janeiro, 4 26.0 × 22.0 mm, 29.7 × 25.5 mm, 31.5 × 27.3 mm, 35.4 × 30.4 mm ( MCZ 6234). — Florianopolis, 1 22.6 × 19.7 mm ( MCZ 6235). — Branner-Agassiz Expedition, 1.VIII.1899, 1, 1 ( USNM 25711). — Santos, Pissaquera, VI.1913, coll. H. Luederwaldt, 2 ( USNM 47859). — Rio de Janeiro, Terra de Masahe, I.1912, coll. E. Garbe, 2 ( USNM 47862). — Santos, Ilha Casquerinita, VI.1913, coll. H. Luederwaldt, 2 juvenile ( USNM 47867). — São Sebastião, 5, 7 ( USNM 70986). — São Francisco, 31.X.1925, coll. W. L. Schmitt, 4, 1 ( USNM 71168). — São Paulo, Ubatuba, mangrove at Praia Dura, 30.VIII.1992, coll. F. L. M. Mantelatto, 2 31.2 × 27.5 mm, 26.0 × 22.8 mm ( ZRC 2000.1780). — São Paulo, Ubatuba, mangrove at Praia Dura, III.1997, coll. F. L. M. Mantelatto, 1 22.6 × 19.9 mm ( SMF 25169).

REMARKS

Sesarma eydouxi was described from Cochin- China but the number of specimens actually available to H. Milne Edwards is not clear. In the MNHN is a type specimen which is here designated as the lectotype of the species ( Figs 4; 5 ) .

A

B

C

31.2 × 27.2 mm ( MNHN B10930); A, dorsal view; B, carapace;

A

B

C

31.2 × 27.2 mm ( MNHN B10930); A, frontal view; B, right chela,

Heller (1865) subsequently reported this species from Madras ( India), and de Man (1880) record- ed it on the basis of specimens from an unknown provenance (measurements of largest male 33.0 × 27.0 mm), and he subsequently redescribed the type (de Man 1892). Tesch (1917) redescribed in detail the specimens of de Man (1880), and made a telling comment: “This species is exceedingly alike Ses. recta Randall of America, and I own to be at a loss to indicate any important point of difference between the two species” ( Tesch 1917: 153).

Sesarma rectum was described from Surinam, and S. muellerii (type locality: Brazil, 30.0 by 27.0 mm) is now generally regarded as its junior synonym (for detailed synonymy, see Tesch 1917: 190; Abele 1992: 15; for recent distribution records, see Schubart et al. 1999). Photographs of Sesarma rectum , a dried type specimen in the Philadelphia Museum ( Fig. 6 ), and S. eydouxi ( Figs 4; 5 ) were compared, and only minimal differences were observed, confirming that the two species are synonymous. The holotype of Sesarma rectum has chelae with 15 more or less evenly spaced dactylar tubercles, whereas the lectotype of S. eydouxi has 14 ( Figs 4C; 5B, C ; 6B, C ). In both cases, the tubercles have corneous tips which are slightly pointing distally (see also Abele 1992: fig. 4b with only 12 tubercles; fig. 9 with 14 tubercles, 14-16 tubercles in text). The upper surface of the chelar palm of both type specimens has a continuous ridge of unpectinated tubercles ( Figs 4C; 5C ; 6C ; 7C ), a typical character for the American species of Sesarma s.s. (see von Hagen 1978; Abele 1992: fig. 2e). The chelar carpus of both types is characterised by a triangular tooth at the inner distal corner and a coarsely granulat- ed outer surface ( Figs 4C; 7C ). The lectotype of S. eydouxi has a slight indication of an anterolateral tooth, without forming a real notch or tooth ( Fig. 4A, B). In the original description, H. Milne Edwards (1853: 184) refers to it as: “Carapace rugueuse, pubescente et obscurément bidentée de chaque côté”. The indicated tooth is not as evident in the type of S. rectum ( Fig. 6B ), but also known from this species: “Slight emargination present, indicated by ridge below angle with second stronger ridge below first” ( Abele 1992: 15, fig. 9). The types of S. rectum and S. eydouxi also agree in the presence of two rows of setae delimiting the epistomial Verwey’s groove ( Figs 5A ; 7B ) (see von Hagen 1978; Abele 1992: fig. 2d), in the shape of the frontal lobes, and in the particularly broad meri of the walking legs ( Figs 4A; 6A ) (meri of fourth walking leg less than twice as long as wide). Based on the measurements taken for us in Paris and Philadelphia, the carapace shapes of the two type specimens appeared to differ substantially. Maximum carapace width divided by maximum carapace length resulted in a ratio of 1.23 for S. rectum and 1.15 for S. eydouxi . Re-measurement of the photographed carapaces, however, revealed a ratio of 1.13 for both types. The measurements obtained by de Man (1892) for the type of S. eydouxi (31.25 × 26.25 mm) resulted in a ratio of 1.19. The discrepancies in the original ratio for S. rectum could be because the width and/or length measurements were taken in a different manner by the ANSP staff.

In summary, the two species are here regarded as synonymous and that the original locality data of S. eydouxi must be incorrect. In fact, numerous collections from around that area and Southeast Asia in general have never uncovered a species even resembling S. rectum . The record of “ S. eydouxi ” from Madras ( India) by Heller (1865: 64) will need to be rechecked – it is not S. eydouxi as presently defined. As indicated by von Hagen (1978) and genetically confirmed by Schubart et al. (1998a), S. rectum clearly belongs to Sesarma s.s., despite the absence of an anterolateral tooth. The genus Sesarma presently contains 16 species, all from the American Atlantic and eastern Pacific ( Abele 1992; Schubart et al. 1998b).

Figures

FIG. 5. — Sesarma eydouxi H. Milne Edwards, 1853, lectotype dorsal view; C, left chela, dorsal view.

FIG. 6. — Sesarma rectum Randall, 1840, holotype 32.8 × 26.7 mm (ANSP 3976); A, overall view; B, carapace; C, front and chelipeds, dorsal view.

FIG. 7. — Sesarma rectum Randall, 1840, 22.6 × 19.9 mm (SMF 25169); A, front, dorsal view; B, frontal view; C, right cheliped, dorsal view; D, right chela, outer view.