Pagurus alarius, Lemaitre, 2020

Lemaitre, Rafael, 2020, New and rare micro-pagurid hermit crabs (Crustacea: Anomura: Paguridae) from the Caribbean Sea and Gulf of Mexico, Zootaxa 4722 (4), pp. 301-325 : 317-320

Pagurus alarius sp. nov.

( Figs 12–14 )

Type material. Holotype: female 1.5 mm, Seagal , Bocas del Toro Province, Panama, Caribbean Sea, 9.289°N, 82.296°W, BBDT-2888, BCS2016-043, 3.0– 3.5 m, lagoon fringing reef, Agaricia reef framework, 27 May 2016, colls M. Leray, F. Michonneau, R. Lasley ( UF 052162).

Description. Eleven pairs of biserial phyllobranch gills. Shield ( Fig. 12A ) approximately as long as broad; dorsal surface glabrous, lacking lineae or grooves except for weakly visible and short linea d, smooth except for few setae on linea d; lateral lobes obsolete. Anterolateral margins sloping. Anterior margins between rostrum and lateral projections weakly concave. Posterior margin truncate. Rostrum obtusely subtriangular, reaching slightly in advance of lateral, projections, terminating in small spine. Lateral projections triangular, with small marginal spine. Posterior carapace membranous; anterior lobe of branchiostegite with setae on distal margin.

Ocular peduncles long, approximately 0.8 length of shield (including corneas), slightly inflated basally, with few scattered short setae; corneas weakly dilated. Ocular acicles subtriangular, terminating in multifid margin of 4 or 5 spines, separated by approximately basal width of 1 acicle.

Antennular peduncle exceeding distal margin of corneas by approximately one-third of ultimate segment when fully extended. Ultimate segment naked except for dorsodistal tuft of setae. Penultimate and basal segments glabrous. Basal segment with small spine on dorsolateral distal margin.

Antennal peduncle exceeding distal margin of corneas by approximately one-half length of fifth segment. Fifth and fourth segments unarmed except for scattered setae. Third segment with strong spine and tuft of setae on ventrodistal margin. Second segment with dorsolateral distal angle produced into strong acute projection terminating in spine; dorsomesial distal angle with small sharp spine, and short setae on mesial surface; first segment unarmed. Antennal acicle reaching to approximately distal margin of cornea, broadly curved outward, terminating in acute spine with tufts of setae; mesial margin with row of long setae. Flagellum long, distinctly overreaching right cheliped; with short setae less than 1 article in length.

Mouthparts not dissected. Third maxilliped ischium with weak crista dentata consisting of row of about 15 minute teeth slightly increasing in size proximally, and strong accessory tooth.

Chelipeds unequal, right longer and distinctly stronger than left. Right cheliped ( Fig. 13 A–C) somewhat compressed dorsoventrally; dactyl and fixed finger leaving narrow hiatus proximally when closed, slightly crossed distally at tips when closed, each terminating in small, blunt corneous claw, cutting edges each with row of small, rounded, calcareous teeth slightly increasing in size distally. Dactyl slightly shorter than palm (measured on mesial margin), dorsal surface naked, with row of small tubercles along weakly elevated midline, and row of mesially directed setae near cutting edge; mesial margin armed on proximal half with strong spines and long setae; ventral surface naked. Fixed finger with scattered small tubercles on dorsal surface; lateral margin with row of strong spines and long setae; ventral surface naked. Palm approximately as long as carpus; dorsal surface nearly naked, with scattered small blunt tubercles or minute spines, median region slightly elevated; lateral and mesial margins armed with strong spines and fringe of long setae directed slightly upwards; ventral surface naked. Carpus approximately as long as merus, with few long setae on dorsal surface; dorsolateral surface rounded, with irregular row of 5 spines; dorsodistal margin with 2 median spines; dorsomesial margin with 3 spines on distal half; ventral surface unarmed except for a few setae. Merus subtriangular; dorsal surface naked; lateral surface smooth, ventrolateral distal margin with 3 spines; mesial surface smooth, ventromesial distal margin with 1 spine; ventral surface glabrous. Ischium and coxa glabrous, latter with few short setae on ventromesial margin.

Left cheliped ( Fig. 13D, E ) with fingers leaving narrow hiatus when closed, terminating in small corneous claws crossed when closed. Dactyl approximately as long as palm, surfaces with scattered short setae; cutting edge with row of fused corneous teeth on distal half; dorsal and ventral surfaces unarmed except for scattered setae and few minute tubercles; lateral surface rounded. Fixed finger with scattered minute tubercles and few tufts of short setae on dorsal surface; cutting edge with small, well-spaced calcareous teeth and row of fused corneous teeth on distal one-third; lateral margin with row of small spines on proximal half. Palm approximately half as long as carpus; dorsal surface with scattered short setae, with 2 rows of small spines medially; lateral margin with row of small spines; mesial surface rounded; ventral surface glabrous. Carpus as long as merus; armed with row of spines on dorsolateral and dorsomesial margins, and strong dorsodistal spine; lateral and mesial surfaces smooth, with scattered tufts of setae; ventral surface glabrous. Merus subtriangular, naked; dorsal and dorsodistal margins unarmed; ventrolateral margin with row of 5 spines increasing in length distally; ventromesial margin with 1 distal spine; ventral surface with few long setae. Ischium and coxa unarmed, latter with short setae on ventromesial margin.

Pereopods 2 and 3 ( Fig. 14 A–D) similar from left to right, except for slightly slenderer and longer segments of left pereopods; dactyls broadly curved distally, each terminating in sharp corneous claw. Dactyl slightly shorter than propodus; dorsal margin with long setae; ventromesial margin with 7 or 8 distinct corneous spinules, and few long setae. Propodus glabrous except for few long setae on dorsal and ventral margins. Carpus with small dorsodistal spine, otherwise unarmed except for few long setae dorsally and ventrally. Merus and ischium glabrous except for few setae dorsally and ventrally. Coxa glabrous except for short setae on ventromesial margin. Sternite XI (of pereopods 3), with anterior lobe ( Fig. 11B ) semi-subcircular, sparsely setose and armed with small spine on distal margin.

Pereopod 4 ( Fig. 14E ) semichelate. Dactyl broadly curved, slender, subtriangular, terminating in a sharp corneous claw, with ventrolateral row of minute, fused corneous teeth; dorsal margin nearly naked. Propodus with few setae on dorsodistal angle; propodal rasp consisting of 2 rows of ovate corneous scales, no preungual process. Carpus with sparse long setae on dorsal margin and ventrodistal angle. Merus nearly naked except for few long setae on ventral margin. Ischium with few setae on ventromesial margin.

Pereopod 5 chelate. Dactyl with long setae on dorsodistal margin. Propodus with row of long setae on ventral surface; propodal rasp occupying approximately one-third of lateral face of propodus. Carpus, merus, and ischium naked or with scattered short setae. Sternite XIII (of pereopods 5; Fig. 12B ), narrow, weakly subdivided into 2 slightly asymmetric narrow lobes, with few setae on distal margin.

Uropods ( Fig. 12C ) strongly asymmetrical; left uropod largest, with fringe of long bristle-like setae on posterior margin. Telson ( Fig. 12C ) nearly symmetrical, with transverse suture; anterior lobes with few setae laterally; posterior lobes separated by deep U-shaped median cleft, with few setae laterally, terminal margins nearly horizontal, each armed with 5 strong blunt or sharp calcareous spines.

Male unknown. Female with paired gonopores; lacking first pleopods, with unpaired left pleopods 2–5.

Color. Unknown.

Etymology. The specific name is derived from the Latin alarius , meaning of wings, and refers to the wing-like similarity of the fringes of long setae on the right chela that characterize this new species.

Distribution. Caribbean Sea, known so far only from Bocas del Toro Province, Panama. Depth: 3.0– 3.5 m.

Remarks. This new species, known exclusively from the female holotype, is assigned for the time being to Pagurus , a catch-all genus for any pagurid with 11 pairs of phyllobranchiate gills and lacking any secondary sexual modifications or similar exclusive characters. Future discovery of males of this new species and their sexual characteristics may require a generic reevaluation of this taxon.

Pagurus alarius sp. nov. is distinct from other species assigned to Pagurus from the western Atlantic most notably by the armature and setation pattern of the right chela ( Fig. 13 A–C) which has on the lateral and mesial margins a fringe of long setae directed obliquely upwards in wing-like fashion. In that character alone, and combined with the presence of a row of bristle-like setae on the posterior margin of the exopod of the left uropod, there is no obvious affinity with other known western Atlantic congeners.

Figures

FIGURE 11. A, Paguriscus robustus Lemaitre, Felder & Poupin, 2017, Bocas del Toro Province, Panama, Caribbean Sea: male, 1.2 mm (UF 044397); B, Nematopaguroides karukera Lemaitre, Felder & Poupin, 2017, Bocas del Toro Province, Panama, Caribbean Sea: ov female in shel 1.8 mm (UF 044300); C, D, Pylopaguridium markhami McLaughlin & Lemaitre, 2001, Bocas del Toro Province, Panama, Caribbean Sea: C, male 1.6 mm (UF 044314); D, male 1.4 mm (UF 044396). Scales: 1.0 mm (A), 2.0 mm (B–D). (Photographs: G. Paulay)

FIGURE 12. Pagurus alarius sp. nov., holotype female 1.5 mm, Seagal, Bocas del Toro Province, Panama, Caribbean Sea (UF 052162): A, shield and cephalic appendages, dorsal; B, sternum and coxae of pereopods 1–5, ventral; C, uropods and telson, dorsal. Scale: 0.5 mm.

FIGURE 13. Pagurus alarius sp. nov., holotype female 1.5 mm, Seagal, Bocas del Toro Province, Panama, Caribbean Sea (UF 052162): A, right cheliped, dorsal; B, same, lateral; C, chela of same, frontal; D, left cheliped, dorsal; E, same, lateral. Scale: 0.5 mm.

FIGURE 14. Pagurus alarius sp. nov., Holotype female 1.5 mm, Seagal, Bocas del Toro Province, Panama, Caribbean Sea (UF 052162):A, left pereopod 2, lateral; B, dactyl of same, mesial; C, left pereopod 3, lateral; D, dactyl of same, mesial; E, propodus and dactyl of left pereopod 4, lateral. Scale: 0.5 mm.