Trichopeltarion dextrum

Trichopeltarion dextrum (Rathbun, 1898)

(Figs 1–3)

Hypopeltarium dextrum Rathbun, 1898: 277, pl. 6, fig. 2.

Peltarion dextrum. — Rathbun 1930: 161.— Soto 1979:165, fig. 1.— Salva & Feldmann 2001: 51.— Ng et al. 2008: 51. Trichopeltarion dextrum.— Tavares & Cleva 2010: 130, figs. 18A–B.

Material examined. 1 adult male (cl 41 mm, cw 38.5 mm), Pará, REVIZEE–N, Leg X, Hauling 5, 01°18’N, 46°31’W, 240 m, mud, 01 June 1999, MOUFPE 13408. 1 adult male (cl 39 mm, cw 38.5 mm), 4 adult females (cl 34 mm, cw 32 mm; cl 36 mm, cw 33 mm), Pará, REVIZEE–N, Leg X, Hauling 5, 01°18’N, 46°31’W, 240 m, mud, 01 June 1999, MOUFPE 13409.

Description. Carapace subcircular about as long as wide broad (1.01 times), maximum width attained between second epibranchial tooth, arched transversely, strongly arched longitudinally. Anterior portion longer than posterior (1.1 times). Front cut into three prominent, forward directed, triangular teeth; central tooth distinctly longer than laterals (1.6 times), bearing three small acute spines (barbs), one apically and one subapically on each side; lateral rostral teeth slender, about 2/3 as long as central tooth, slightly divergent. Central and lateral rostral teeth covered with stiff setae; a tuft of setae hairs between each frontal tooth. Orbits large, directed laterally; orbital margin cut into two dorsal spines and lobe; inner orbital spine with four spinules distally separated from front by deep notch V–shaped, and from upper orbital lobe by deep sinus; outer orbital spine separated by upper orbital lobe by deep sinus; orbital margin dorsally with numerous spinules. Lateral margin of carapace rounded, with numerous spinules, marked by four weakly developed broad triangular teeth, including outer orbital tooth, other teeth being two anterolaterals, one posterolateral. Dorsal surface of carapace paved with numerous well-separated, small, white tipped spines. Surface between spines with some short, stiff hairs. Frontal region sparsely tuberculated behind frontal teeth and orbits. Other regions of carapace separated by shallow, smooth grooves. Mesogastric region with axial row of acute spinules. Pterygostomial region almost smooth, shining. Posterior margin of carapace with 33.4° inclination.

Thoracic sternum with some granules, longer than wide; maximum width attained at sternite 5. Third sternite with two lateral expansions.

Eyestalks slender, retractile within orbits. Cornea well-developed and brown; a small spine near anterior tip of eyestalk.Antennules folded longitudinally. Basal article of antennal peduncle almost attaining end of inner suborbital tooth, lying imperfectly within inner hiatus of orbit, short, subcylindrical, imperfectly fused to carapace; next two articles successively much slenderer; flagellum coarse, stout, setose. Epistome well defined, sunken, overlapped by third maxillipeds. Buccal frame squarish, longer than broad, anterior margin weakly defined, incompletely covered by somewhat elongate.

Third maxillipeds, merus narrower than ischium, rounded at anteroexternal angle, obliquely truncated at anterointernal angle; ischium wider distally than merus, anterointernal angle produced; inner angle spinulous.

Chelipeds strongly unequal, right massive, much larger than left. Merus and carpus upper margins spinous. Carpus lower margin smooth; upper margin ending in strong triangular process, with spinules. Propodus palm upper margin spinous; lateral surface sparsely spinous, smooth in the median part; inner surface smooth. Dactylus almost smooth, as long as and more curved than fixed finger, ending in short subacute tooth; cutting edge armed with blunt, shallow teeth; fixed finger almost smooth, slightly curved, ending in short subacute tooth; cutting edge with blunt teeth. Left cheliped merus outer surface, carpus and propodus heavily tuberculated, ornamented with sparse setae. Propodus outer surface of propodus tuberculated, at least with four recognizable longitudinal lines of subacute tubercles; dactylus longer than fixed finger and armed with acute spines. Pereopod 1 propodus and carpus upper margin spinulous.

Pereopods 2–4 merus upper margin with small spine near distal end. Pereopod 5 merus outer surface with row of spinules. Dactylus of all pereopods longer than propodus.

Male abdomen with six free segments and telson sparsely covered with fine setae; telson broader than long, not invaginated into the preceding segment. Sixth abdominal segment longer than preceding ones, squarish, anterolateral angles only slightly protruded, weakly swollen. Abdominal surface setose, without spinules or granules. Transverse line of tubercles on first abdominal segment; three tubercles, forming triangle, on second abdominal segment. Pair of tubercles of press-button system on middle of fifth sternite.

Female (sexually dimorphic characters only). Resemble male but is more setose than the male. Carapace with more developed spines, inner orbital tooth less developed than males, hepatic spine more developed. Chelipeds equal. First abdominal segment with row of spines, second and third segments with two tubercles in transverse line.

Variations. Central rostral teeth with or without spines; eyestalk with or without spines on inner margins. Dorsal surface of carapace with spines acute or blunt. Male carapace length/width 1.01–1.06 and female carapace length/width, 1.06–1.09.

Geographic distribution. Mexico, off Cozumel Island - Yucatan (Rathbun 1930, Soto 1979), Saint Vicente Island (Soto, 1979), between 203 and 422 m depth. Brazil, Pará, at 240 m depth (present study) (Fig. 4).

Remarks. The present species fits well with diagnostic characters of Trichopeltarion dextrum provided by Rathbun (1898), Soto (1979) and Tavares & Cleva (2010). Although the type material of T. dextrum is composed of only the holotype male, there are no doubts about its validity. This species was described based on material collected by “Albatross” off the Island of Cozumel, Yucatan, at 416 m depth. After that, Soto (1979) examined three female specimens, being two subadults (cw 13.7–14.8 mm) and one adult (cw 33.4 mm) from “Gerda” Sta. 889, Arrowsmith Bank (20°55’N 86°20’W) at 203 m and “J. E. Pillsbury” Sta. 876 off St. Vincent (13°13.9’N 61°04.5’W) at 239 m, which were identified T. dextrum. Although the type series is composed of only one male, he assumed that most carapace differences between his material and holotype were caused by sexual dimorphism. However, regarding the degree of convexity of the carapace, cited by him as becoming less accentuated as the body increases in size, we observed no particular differences in Brazilian female material. The shape of carapace in the holotype male (cl 42 mm, cw 36 mm) is ovate, while in both males from Brazil (adult: cl 41 mm, cw 38.5 mm; subadult: cl 39 mm, cw 38.5 mm), it is almost as long as wide; also, the hepatic, first, and second epibranchial teeth are less developed than the holotype. Another feature of carapace that varies among the specimens (males and females) is the aspect of the tubercles that cover the entire surface of the carapace. In subadult females, the tubercules are more acute and defined, being blunt in adults; sometimes the blunt one is localized on the central part of carapace. Comparing male specimens, the subadult form has acute tubercles near the lateral margins of carapace only, while in adults all of tubercles are blunt.