Armases roberti (H. Milne Edwards 1853)

Armases roberti (H. Milne Edwards, 1853)

Sesarma roberti H. Milne Edwards, 1853:182.—Guinot, 1988:8.

Sesarma americana.—Pocock, 1889:7 [not S. americanum de Saussure].

Sesarma bromelium Rathbun, 1896:143.

Sesarma (Holometopus) roberti.—Rathbun, 1897a:90.—Tesch, 1917:193.—Rathbun, 1918:312, pl. 91.—Monod, 1956:443, figs. 602–604.—Chace and Hobbs, 1969:184, figs. 60, 621–62n.

Sesarma (Holometopus) angustipes.—Rathbun, 1918:311, pl. 90.—Hartnoll, 1965:113, 115, 131–133, 144, 146, figs. 10B, 11B,D, 15A,B [not S. angustipes Dana].

Sesarma miersi.—Rodriguez, 1980:383, fig. 106 [see p. 493].

Sesarma angustipes.—Rodriguez, 1980:393, fig. 108 [see p. 493].

MATERIAL EXAMINED.—Jamaica: Montego Bay, 1, 20, 29 Aug 1910, E.A. Andrews, USNM 42878; 8, 13, 3 Aug 1910, E.A. Andrews, USNM 42876; near Meneague, 1, W.G. Lynn, USNM 74544; Gray's Inn, 1, 1, 1928, C.R. Orcutt, USNM 61367.

St. Lucia: Port Castries, 1, USNM 22108.

Cuba: Bahia Honda, 2, 1, 1 ovigerous , USNM 48580; Soledad, Cienfuegos, 1, J. Welsh, USNM 63312; Belmonte Brook, 1, 2, 23 Aug 1930, R. Dow, MCZ 8990.

Barbados: St. Joe's River, 3, 4, 20 Apr 1937, Smithsonian-Hartford Expedition, USNM 73317.

Haiti: Near Grant Anse River, 2, 2, W. Faxon, USNM 81357; same locality, 20, 29 (3 ovigerous), MCZ 6226; Diquini, 2, 3 (2 ovigerous), Nov 1912, W. Mann, MCZ 8939; Jeremie, 7, 3, D.F. Weinland, MCZ 1582.

Trinidad: 3, 2 (1 ovigerous), Oct 1971, J.M. Stonley, USNM 139302.

Santo Domingo: River 7 km SE of Porto Playa, Jul 1937, W.J. Clench, MCZ 9870; same locality, 1, 2 (2 ovigerous), MCZ 9865; Barbour Harbor, 3 (1 ovigerous), AMNH 10045.

Tobago: Speyside, Doctor's River, 2, AMNH 13835.

DESCRIPTION.—Carapace subquadrate (cl/cb = 0.98±0.01), length approximately equal to breadth; slightly convex anteriorly and laterally; lateral striae present; lateral margins converging slightly anteriorly; interorbital region subdivided into four distinct lobes, deep sinus medially, iw/cb = 0.54±0.005; lateral margins of frontal region parallel, anterior margin concave medially.

Eyes well developed, pigmented.

Chelipeds sexually dimorphic, female chelae relatively smaller and smoother than male. Posterior medial margin of merus weakly granular, anteromedial toothed, expanded distally; tuft of setae on distal interior surface. Carpus granular, granules large, sharp on flexor margin. Palm granular, medial surface with large, acute granules. Movable finger granular dorsally; both fingers with corneous spooned tips.

Walking legs long, relatively slender; merus of fourth pereiopod with length about three times width (ml/mw = 2.97±0.09). Propodus and dactylus with long black setae; propodus with short black spine ventrally; dactylus with short black spines on ventral and dorsal surfaces. Females with few setae and spines compared to males. Dactylus slightly shorter than propodus.

Male abdomen triangular in outline; width of telson subequal to length. Male gonopod straight; endpiece flattened with deep sharp sinus distally (V-shaped).

Female abdomen subcircular in outline; width of telson slightly greater than length. Female gonopore subcircular with small projection anteriorly; operculum raised with U-shaped portion around projection. Eggs small and numerous.

COLOR IN LIFE.—From Chace and Hobbs (1969:184–185):

Ground color of carapace tan to dark brown with cream to straw markings: hepatic and protogastric regions with one to four small subcircular cream spots, and protogastric regions with larger spot adjacent to posteromesial margin; branchial regions with four or five spots, often smaller than those on hepatic and protogastric regions; mesogasric region often with pair of small spots forming transverse row with large posteromesial spots in protogastric region. Grooves delimiting mesogastric portion of carapace pale, particularly along posterior margin. Anterolateral and, to more marked degree, posterolateral portions of branchial region with series of subparallel, very thin, light lines directed parallel to posterolateral margin of carapace, lines short anteriorly but increasing in length posteriorly. Front dark brown to black.

Eyestalks dark red; cornea chartreuse, often with dark brown spot posterodorsally. Third maxillipeds cream with dark brown to buff fringes of setae. Chelipeds darker above than below; merus magenta fading ventrally to pinkish cream; carpus reddish purple above fading to pinkish mauve below; propodus purple on palm with gradation along base of immovable finger to orange, lower surface diluted with cream or white; dactyl mostly orange with bright red triangular spot at base of mesial surface. Pereiopods dark grayish brown above, bluish gray below; merus and carpus with irreular and variable darker brown and tan splotches; tip of dactyl yellowish straw; setae dark red. Sternum, basal podomeres of legs, and abdomen pinkish cream with reticulate pattern of bluish gray; sternal plate between chelipeds with mauve suffusion; margin of telson orange.

The females of this species seem to have a more regularly banded pattern on the walking legs than do the males, and even the chelipeds bear conspicuous bands and irregular markings.

MEASUREMENTS.—Males, cb 14.8 to 27.0 mm; females, cb 12.5 to 22.3 mm, ovigerous females cb 17.5 to 23.5 mm.

TYPE LOCALITY.—Goree, Senegal (almost certainly an error, Monod 1956).

TYPE.—Seven syntypes are in the Muséum National d'Histoire Naturelle, Paris (J. Forest, personal comm.); two syntypes are in the National Museum of Natural History, Smithsonian Institution.

DISTRIBUTION.—West Indies (Cuba, Jamaica, Hispaniola, St. Lucia, Barbados, Tobago, Trinidad). All of the material from the mainland of Central and South America reported to be this species belongs to other species. I have not seen any specimens collected on the mainland.

HABITAT.—Sesarma roberti is an extremely common semiterrestrial crab occurring along the banks of freshwater streams and seepage areas. Chace and Hobbs (1969) report them from just above sea level to about 330 m elevation. The same authors report ovigerous females at least 2.5 km upstream from the mouth of the Layou River on Dominica.