Triacanthoneus toro n. sp.

(Figs. 1–4, 10 A–C)

Type material. Holotype: ovigerous female (CL 4.1 mm), USNM 1145375, Panama, Caribbean coast, Bocas del Toro, Isla Colón, Punta Caracol, subtidal sand flat with rubble and sparse seagrass, near mangroves, depth 1.5 m, under rubble in sand, coll. A. Anker, 1 April 2008, fcn 08-022. Paratypes: 1 ovigerous female (CL 3.4 mm), USNM 1145376, Panama, Caribbean coast, Bocas del Toro, Isla Colón, Punta Caracol, subtidal sand flat with rubble and sparse seagrass, near mangroves, depth 1.5 m, under rubble in sand, coll. A. Anker, J.A. Baeza, I. Marin, 28 April 2007, fcn 07-156 (dissected); 1 ovigerous female (CL 3.4 mm), OUMNH.ZC 2010- 01-005, same collection data as for previous specimen, fcn 07-157; 1 ovigerous female (CL 2.5 mm), UP, Bocas del Toro, east of Isla San Cristobal, Laguna Porras, Sta. 9, 9º16’514”N, 82º14’833”W, depth 7 m, loose coral rubble, coll. S. De Grave & M. Salazar, 2 August 2005, fcn 08-254.

Description. Small-sized alpheid shrimp. Carapace with one strong sharp mediodorsal tooth situated slightly posterior to carapace mid-length and two strong sharp dorsolateral teeth situated ventral and anterior to mediodorsal tooth, in post-hepatic area (Figs. 1, 2 B, D). Rostrum straight, more than 1.5 times as long as broad at base; lateral margins slightly concave; tip overreaching distal margin of first segment of antennular peduncle; ventral margin with distinct, anteriorly directed subapical dent; rostral carina well developed, reaching posteriorly to mediodorsal tooth; orbital teeth absent (Fig. 2 A–C). Pterygostomial angle not protruding anteriorly, broadly rounded (Fig. 2 B).

Pleura of first to fourth abdominal somites rounded posteroventrally; fifth pleuron with posteroventral angle produced in small tooth (Fig. 1). Telson narrow, at least 3.5 times as long as wide in proximal third, tapering distally; dorsal surface with two pairs of strong spiniform setae situated at some distance from lateral margins, at about 0.5 and 0.8 telson length, respectively; posterior margin straight, each posterolateral angle with two pairs of spiniform setae, mesial being 0.6 times as long as lateral, and two plumose setae between mesial spiniform setae (Fig. 2 L, M).

Eyes partly exposed in dorsal and lateral views; cornea somewhat reduced, well pigmented, occupying anterolateral portion of eyestalk, anteromesial margin with small blunt process (Fig. 2 A, B).

Antennular peduncle stout, with second segment distinctly longer than wide; first segment with distally acute stylocerite reaching to about 0.4 length of second segment; ventromesial carina of first segment with anteriorly directed tooth; lateral flagellum biramous, fused portion composed of at least three segments; accessory ramus composed of four or so partly fused segments with groups of aesthetascs (Fig. 2 A, B, F). Antenna with stout basicerite bearing sharp distoventral tooth; scaphocerite reaching to end of antennular peduncle, ovate; blade broad, with anterior margin convex, reaching slightly beyond strong distolateral tooth; carpocerite barely reaching 0.5 length of scaphocerite (Fig. 2 A, B, G).

Mouthparts typical for genus, as illustrated (Fig. 3 A–F). Third maxilliped with coxa bearing rounded lateral plate above mastigobranch; antepenultimate segment elongate, flattened; penultimate segment elongate, slender; ultimate segment tapering distally, ending in corneous tip, without robust setiform setae on apex; arthrobranch well developed (Fig 3 G).

Chelipeds very unequal in size and asymmetrical in shape, carried folded (Fig. 4 A, D). Major cheliped enlarged, elongate, slender; ischium rather long, slender, ventrolateral surface with three stout spiniform setae; merus much longer than ischium, slender, smooth, ventrally flattened; carpus distinctly shorter than merus, subcylindrical, distally somewhat broadening, smooth; chela subcylindrical, smooth; fingers longer than palm, compressed, slightly twisted, cutting edges evenly serrated, with at least 18 subtriangular teeth (Fig. 4 A–C). Minor cheliped not particularly enlarged, slender; ischium long, ventrolateral surface with three stout spiniform setae; merus slightly longer than ischium, somewhat compressed, smooth; carpus slightly shorter than merus, subcylindrical, slightly widening distally, smooth; chela simple, smooth, with fingers slightly longer than palm, finger cutting edges straight, except for a few small distal teeth (Fig. 4 D, E).

Second pereiopod slender; ischium about as long as merus, with three spiniform setae on ventrolateral surface; carpus five-segmented, first segment longest, slightly longer than sum of four other segments, ratio of carpal segments (from proximal to distal) more or less equal to: 5.5: 1: 1: 1.5: 1.5; chela simple, longer than most-distal carpal article (Fig. 4 F). Third pereiopod very slender, compressed; ischium elongate, with two spaced spiniform setae on ventrolateral surface; merus elongate, almost 10 times as long as wide, smooth; carpus longer than merus, with slender stiff distoventral seta; propodus with one slender spiniform seta on ventral margin and one stouter distal spiniform seta adjacent to dactylus; dactylus almost 0.5 propodus length, simple, conical, very slender, gradually curving distally, furnished with setae on dorsal margin (Fig. 4 G, H). Fourth pereiopod almost identical to third pereiopod. Fifth pereiopod longer and more slender than third or fourth pereiopods; ischium unarmed; carpus distinctly longer than merus, propodus with two small spiniform setae on ventral margin and at least six rows of slender serrulate setae on distolateral surface, most-distal row with longest setae reaching well beyond dactylar base (Fig. 4 I).

Second pleopod of all four (ovigerous) specimens with appendix interna and appendix masculina, latter shorter than appendix interna, with stiff apical and subapical setae (Fig. 2 I). Uropod with lateral lobe of protopod ending in small subacute tooth; exopod and endopod slender; exopod with sinuous diaeresis and blunt distolateral tooth adjacent to robust spiniform seta (Fig. 2 J, K).

Gill-exopod formula as described for genus (see above).

Colour in life semitransparent-white, gonads yellow (Fig. 10 A–C).

Etymology. Specific name derived from the third word of the type locality, Bocas del Toro; toro also means bull in Spanish, alluding to the two horn-like projections on the carapace; used as a noun in opposition.

Habitat. Sand flats with abundant rubble and seagrass, at some distance from fringing mangroves, at depth range of 1.5–7 m; most specimens were found on sand deep under large pieces of rubble, one was found among loose rubble.

Type locality. Bocas del Toro, Caribbean coast of Panama.

Distribution. Presently known only from the type locality on the Caribbean coast of Panama.

Remarks. One of the paratypes has a somewhat aberrant rostrum, with two instead of one subapical dent (Fig. 2 N).