Paguriscus robustus Lemaitre, Felder & Poupin, 2017

(Figs 8–10, 11A)

Paguriscus robustus Lemaitre, Felder & Poupin, 2017: 175, figs 16, 17, tab. 1; Poupin, 2018: 163. Material examined. Bocas del Toro Province, Panama, Caribbean Sea: 19 males 0.7–1.2 mm, 5 females 0.7– 1.0 mm, 16 ov females 0.9–1.3 mm, 12 specimens unsexed, unmeasured [in shells] runway, 9.342°N, 82.260°W, BBDT-1291, BCS2016–023, 4.0– 4.5 m, lagoon fringing reef, Agaricia reef framework, 19 May 2016, colls M. Leray, F. Michonneau, R. Lasley (UF 044397); 5 males 0.9–1.3 mm, same locality, depth, date and colls as previous, BBDT-2085, BCS2016–034, 23 May 2016 (UF 044437); 1 ov female, 1.2 mm, Cayo Roldán, 9.215°N, 82.324°W, BBDT-0902, BCS2016–016, 1.5–2 m, lagoon fringing reef, Agaricia reef framework, 17 May 2016, colls M. Leray, F. Michonneau, R . Lasley (UF 044347); 1 male 1.4 mm, same locality and data as previous, BBDT-0904, BCS2016–016 (UF 044349) .

Recognition characters. Shield (Fig. 8A) glabrous, at most with scattered short setae, slightly longer than broad. Rostrum bluntly subtriangular, reaching distally to about same level of lateral projections. Lateral projections subtriangular, terminating in small sharp spine. Ocular peduncles short and stout, about 0.6 length of shield; corneas weakly dilated. Ocular acicles subtriangular, terminating in strong distal spine. Ultimate antennular segment with 2 long dorsodistal bristles. Antennal peduncle acicle exceeding distal margin of cornea by about 0.3 length of acicle, broadly curving outward and terminating in strong spine, unarmed mesially except for few short setae; flagellum with scattered short setae each less than 1 flagellar article in length. Chelipeds sparsely setose. Right chela (Fig. 8B) smooth, glabrous, lacking spines, mesial margin of palm, and dorsolateral margins of fixed finger and anterior half of palm weakly but distinctly delimited by a low, minutely denticulate ridge; carpus with 3 spines on dorsodistal margin. Palm of left cheliped (Fig. 8C, D) with median ridge-like elevation armed with few minute tubercles or spines. Pereopods 2 and 3 (Fig. 9 A-D) with dactyls each armed with ventromesial row of 8–10 long, slender spinules; carpus with dorsodistal angle blunt. Anterior lobe of sternite XI (of pereopods 3; Fig. 10A, B) subsemicircular. Pereopod 4 with dactyl lacking preungual process; propodal rasp (Fig. 9E) with single row of rounded corneous scales. Sternite XIII (of pereopods 5) narrow (Fig. 10A, C), anterior lobe bilobed. Uropods (Fig. 10D) markedly asymmetrical, left largest. Telson (Fig. 10D) nearly symmetrical, longer than broad; terminal margins of posterior lobes weakly oblique, each armed with 3 or 4 minute spines. Males with coxae of pereopods 5 extended posteriorly as paired, subequal, stout and calcified sexual tubes (Fig. 10C). Females with unpaired left gonopore (Fig. 10A); with left unpaired pleopods 2–5 (pleopod 5 not ovigerous), eggs relatively few (ranging 5–22) and large (maximum diameter approximately 0.4 mm).

Color (Fig. 11A). Overall evenly semi-transparent light brownish except for white corneas, and whitish tone near articulation of segments in pereopods 2 and 3 (ambulatory legs).

Distribution. Caribbean Sea, from Guadeloupe, and Bocas del Toro Province, Panama. Depth: 1.5– 19 m.

Remarks. Lemaitre et al. ’s (2017 original description of the genus Paguriscus and its single species P. robustus was based exclusively on the incomplete male holotype missing the left cheliped and all other pereopods except the right cheliped and right pereopod 3. Thus, the generic diagnosis and species description was lacking in regard the morphology of the missing appendages and the characteristics of the female. Herein are reported numerous additional specimens of both sexes from Bocas del Toro, Panama, which have allowed to document the condition of the female as well as a complete documentation of the morphology and distribution of P. robustus . The new specimens also show that this species occurs broadly in the Caribbean, and is now known from the eastern (Guadeloupe) and western end (Bocas del Toro, Panama).

The presence of unpaired gonopores in females of Paguriscus robustus is yet another important character that justifies placing this species in a genus of its own, and thus is herein considered diagnostic of Paguriscus . Unpaired gonopores is a sexual character that appears to be unique among hermit crabs of the diverse family Paguridae, where species of at least 12 genera have this condition, and to all species of the deep-water family Parapaguridae, and is typically considered to be of generic level significance.

There is only a small degree of sexual dimorphism in Paguriscus robustus, with females having slightly shorter and less strong right chelipeds than in males. The left cheliped in both sexes is similar, with the palm (Fig. 8D) having a distinctly raised median ridge armed with minute spines. Females have unpaired left pleopods 2–5 (pleopod 5 not ovigerous), and when ovigerous carry relatively few, large eggs.