Sesarma aequatoriale Ortmann 1894

Sesarma aequatoriale Ortmann, 1894

Sesarma aequatorialis Ortmann, 1894:722, pl. 23: figs. 14, 14k, 14z [type locality Ecuador].

Sesarma (Sesarma) aequatorialis.—Rathbun, 1897b:112.—Nobili, 1901:44.

Sesarma (Sesarma s.s.) aequatorialis.—Tesch, 1917:128.

Sesarma (Sesarma) aequatoriale.—Rathbun, 1918:292, fig. 146.

Sesarma (Sesarma) sulcatum.—Rathbun, 1918:289 [in part, see material examined].

Sesarma sulcatum.—Crane, 1947:86 [at least ovigerous female and juveniles from Golfito, male = S. sulcatum].—Abele, 1976:268 [in part, 1 male].

Sesarma aequatoriale.—Abele and Blum, 1977:246.—Abele, 1977b:495, figs. 1, 2, 5c,d; 1981:437.

MATERIAL EXAMINED.—Mexico: Guerrero, 3, 3, 4 Jan 1933, Velero, AHF 3-33; Acapulco, 1, Hassler Expedition, MCZ 6244.

Costa Rica: Boca de Jesus, 1, Apr 1905, Biolley and Tristan, USNM 32315; Golfito, 1 ovigerous , 3 juveniles, 6–7 Mar 1938, Zaca, AMNH 13508.

Panama: El Real, 18, 11, 1 ovigerous , 26 Oct 1966, R. Rish, USNM 125916 (4, 1), AHF 1967-88 (remaining specimens); Chucunaque River, 1, 26 Nov 1965, D. Quintero, USNM 119853; La Capitana (Canal Zone), 1, H. Pittier, USNM 45532; San Jose Island, Pearl Islands, river at Playa Grande, 1 ovigerous , 20 May 1973, L. Abele, R. Dressler; Rey Island, Pearl Islands, 1, 3, coll., 19 May 1973, L. Abele, R. Dressler; Diablo mangrove swamp; 1, 18 Feb 1969, L. Abele; Albrook Air Force Base mangrove swamp; 2, 2, 6 May 1969, L. Abele; same locality, 1, 18 Jun 1974, L. Abele.

Ecuador: 2, 1 (syntypes), 1874, Reiss, MZ; Esmeraldas, 1, E. Festa, MIZS Cr. 114.

DESCRIPTION.—Carapace wider than long with low but distinct granules dorsally along with scattered tufts of pubescence (cl/cb ratio 0.834±0.02 for females). Ratio varies with size, about 0.78 in small males and 0.86 in large males; 0.83 in small females and 0.85 in large females. Lateral margins subparallel although posterior carapace may widen slightly in small specimens and narrow slightly in large males. Interorbital region subdivided into four low lobes; median sinus deeper than submedial pair. Frontal region concave medially; oblique laterally to lateral margins that flare slightly so that frontal region widens distally (iw/cb ratio is 0.597±0.02 in males and 0.588±0.02 in females). Outer orbital angle extended anteriorly and acute; distinct lateral tooth present posterior to outer orbital angle. Both outer orbital angle and lateral tooth variable in size, often larger and more acute than in syntype figured. About seven granular ridges on lateral surface of carapace.

Eyes well developed, pigmented.

Chelipeds sexually dimorphic, male chelipeds large, robust. Posterior mesial and lateral borders of merus weakly serrated; serrations of latter end proximal to distal margin, anterior mesial margin toothed. Carpus covered with short rows of granules. A distinct row of large granules along dorsal margin of palm; lateral surface smooth to punctate while mesial surface with about 10 large tubercles arranged in poorly defined dorsoventral row. Immovable finger narrows distally to corneous, spooned apex; about 7 to 13 unequal teeth present. Movable finger with row of 10 to 14 acute tubercles along dorsal margin; a large basal tooth and about eight smaller teeth proximal to a larger tooth present proximal to tip. Female chelipeds considerably smaller than those of equal-sized mature males. Palm lacks tubercles on mesial surface and movable finger has only five or six weak tubercles on dorsal margin.

Walking legs increase in length in order: first, fourth, second, and third. For third walking leg (fourth pereiopod) merus about 1.6 times length of carpus; carpus slightly shorter than propodus; dactylus about times length of propodus. Merus length about twice width (ml/mw = 2.19±0.13 in males, 2.06±0.12 in females); transverse rows of granules present and a large subdistal tooth on dorsal margin. Merus of fourth walking leg (fifth pereiopod) broader than that of third (ml/mw = 2.03±0.10). Walking legs with a ventral and dorsal row of thick pubescence extending from dorsal distal part of carpus to distal margin of propodus; it continues as three narrow rows on dorsal surface of dactylus; ventrally row begins on distal part of propodus and continues as three narrow rows on dactylus. Ventral surface of propodus armed with about five closely set pairs of spines in three indistinct rows, about six dark-colored spines on each side of ventral distal margin.

Male abdomen subtriangular in outline; length and width of telson subequal. Endpiece of male gonopod relatively long; sinus on distolateral margin. Form of sinus somewhat variable, may consists of only a concavity. In almost all (80%) specimens examined endpiece damaged to some extent along sinus margin.

Female abdomen semicircular in outline. Female gonopore and operculum figured (Figure 17).

MEASUREMENTS.—Males, cb 9.7 to 24.1 mm; females, cb 10.5 to 24.3 mm; ovigerous females cb 16.4 to 21.0 mm; males larger than about cb 19.0 appear to be sexually mature, whereas females appear to attain sexual maturity at about cb 16.0 mm.

TYPE LOCALITY.—Ecuador.

TYPE.—The syntypes (two males, two females) are extant in the Museo ed Istituto di Zoologica Sistematica, University of Torino, Italy.

DISTRIBUTION.—This species is known from Acapulco, Mexico, Costa Rica, Panama, and Ecuador.

HABITAT.—Sesarma aequatoriale is a semiterrestrial species that occurs in and adjacent to fresh and brackish water streams and rivers. Specimens of S. aequatoriale and pseudothelphusid crabs were collected from Rio Chepillo (actually a small stream) on Isla Rey in the Pearl Islands, Panama. An ovigerous female was collected from a large unnamed river that empties into Playa Grande, Isla San Jose, Pearl Islands, Panama. Specimens were also collected from mud flats adjacent to a brackish stream and in a brackish water mangrove swamp on the mainland of Panama. All of the specimens I collected were under rocks and debris; none was in a well-defined burrow. The salinity range of S. aequatoriale is 0 to 22.40/00 although the species appeared to be more common around lower salinity water. In freshwater streams S. aequatoriale occurs with pseudothelphusid crabs; at higher salinities it occurs at various localities with S. sulcatum, S. rhizophorae Rathbun, 1906, S. rubinofforum Abele, 1973b, and A. occidentale (Smith, 1870).