Triacanthoneus blanca, Anker, 2020

Anker, Arthur, 2020, Taxonomic remarks on the alpheid shrimp genus Triacanthoneus Anker, 2010 with description of a second eastern Pacific species (Malacostraca: Decapoda), Zootaxa 4772 (3), pp. 450-468 : 457-460

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Triacanthoneus blanca

sp. nov.

Triacanthoneus blanca sp. nov.

Figs. 1–4 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4

Type material. Holotype: non-ovigerous specimen (cl 3.8 mm), FLMNH UF 51919 , Panama, Pacific coast, Coiba Archipelago , off eastern coast of Isla Coiba, Granito de Oro islet, north side, 7°35’59.9”N 81°43’01.1”W, mixed rock-sand-rubble bottom, depth: 8–10 m, under large rocks and rubble on sand, dip net, leg. B. Figuerola & M. Leray, 20 February 2019 [PAN-187A]. GoogleMaps

Description. Small-sized (holotype at cl 3.8 mm) alpheid shrimp with slender, somewhat elongate, non-compressed body. Carapace, pleon and telson glabrous, not particularly setose. Carapace with two strong, sharp, anteriorly directed teeth in post-hepatic position, one on each side, and similarly strong, sharp, anteriorly directed tooth on mid-dorsal carina, slightly posterior to carapace mid-length (extending between about 0.55 and 0.65 of carapace length including rostrum); three stout erect setae arising in front of dorsal tooth ( Fig. 1 View FIGURE 1 A-C). Rostrum well developed, moderately long, reaching distal margin of first article of antennular peduncle, slightly raising anterodorsally (up-turned) in lateral view, about 1.5 times as long as wide at base in dorsal view, acute distally, lateral margins slightly concave; ventral rostral carina with anteroventrally pointing, large, subdistal tooth; rostral carina well developed, continuing as dorsal carina ( Fig. 1 View FIGURE 1 A–C). Orbital teeth indicated as small rounded bumps ( Fig. 1A View FIGURE 1 ). Pterygostomial region broadly rounded; anterolateral suture present; cardiac notch well developed ( Fig. 1C View FIGURE 1 ). Each epistomial sclerite with moderately developed, blunt process.

Pleon with first to fourth pleura posteroventrally broadly rounded to slightly angular; fifth pleuron with posteroventral angle produced into small subacute point; sixth pleonite noticeably elongate, without articulated plate, posterior margin produced into sharp tooth flanking telson ( Fig. 1D View FIGURE 1 ); preanal plate broadly rounded. Telson slender, subrectangular, strongly tapering distally, about 2.3 as long as maximal (proximal) width; dorsal surface with two pairs of slender cuspidate setae inserted at small distance from lateral margin, first pair at about 0.4 of telson length, second pair at about 0.7 of telson length; posterior margin slightly more than half of maximal telson width, straight, with two pairs of spiniform setae of about equal thickness, mesial about 1.5 times longer than lateral, four long plumose setae and one pair of shorter, obliquely dorsally directed setae ( Fig. 1E View FIGURE 1 ).

Eyes partly concealed in dorsal view, largely exposed in lateral view; cornea relatively small (relative to carapace), somewhat square-shaped, with rather few large ommatidia; anteromesial margin of eyestalk protruding as conspicuous subacute process ( Fig. 1A, C, F View FIGURE 1 ).

Antennular peduncle moderately stout; stylocerite with sharp dorsal carina ending anteriorly in acute, dorsally directed tooth, tip reaching well beyond distal margin of first article, slender, acute; ventromesial carina with small, anteriorly directed tooth; second article elongate, 1.7 times as long as wide in dorsal view; lateral antennular flagellum with fused portion consisting of six or so subdivisions, secondary ramus well-developed, with several groups of aesthetascs distally ( Fig. 1A, C View FIGURE 1 ). Antenna with basicerite moderately stout, its distoventral margin with slender acute tooth; scaphocerite oval-rectangular, not reaching end of antennular peduncle, with straight lateral margin and broad blade, latter overreaching stout sharp distolateral tooth; carpocerite very short, cylindrical, reaching midlength of scaphocerite; flagellum slender, not significantly stouter than antennular flagella ( Fig. 1A, C View FIGURE 1 ).

Mouthparts not dissected, typical for genus in external observation. Third maxilliped slender, pediform; coxa with lateral plate slightly subrectangular in shape, dorsal and ventral margins rounded; antepenultimate article slender, slightly flattened ventrally; penultimate article about four times as long as wide; ultimate article with numerous rows of short serrulate setae and fewer longer simple setae, with subacute corneous tip; arthrobranch well developed ( Fig. 1G View FIGURE 1 ).

Chelipeds very asymmetrical in shape and dissimilar in size, carried flexed when not in use, both slender ( Fig. 2 View FIGURE 2 ). Major cheliped moderately enlarged but elongate, overall slender; ischium long, slender, ventrolateral surface with three stout cuspidate setae; merus longer than ischium, slender, smooth, flattened ventrally; carpus about 0.8 times as long as merus, subcylindrical, distally widening, smooth; chela moderately enlarged, somewhat swollen, smooth, flattened laterally; fingers much shorter than palm, compressed, pollex with about 14 subtriangular to rounded teeth on mesial ridge of cutting edge (tip broken in the holotype); dactylus with 11 similar, more spaced teeth on lateral ridge of cutting edge, most proximal and most distal teeth smaller ( Fig. 2 View FIGURE 2 A–D). Minor cheliped not particularly enlarged, somewhat elongate, overall slender; ischium long, slender, ventrolateral surface with three stout cuspidate setae; merus subequal to ischium in length, somewhat depressed ventrolaterally, smooth; carpus 0.9 times as long as merus, subcylindrical, slightly widening distally, smooth; chela simple, smooth, with fingers slightly longer than palm, their cutting edges unarmed ( Fig. 2E, F View FIGURE 2 ).

Second pereiopod very slender; ischium with three small cuspidate setae unevenly spaced on ventrolateral surface; merus subequal to ischium in length; carpus with five subdivisions, first longer than sum of others, with ratio approximately equal to 5.5/1.0/1.0/1.5/1.3; chela longer than distal-most carpal subdivision, simple ( Fig. 3A, B View FIGURE 3 ). Third pereiopod very slender; ischium with two stout cuspidate setae on ventrolateral surface; merus about 10.5 times as long as wide, unarmed; carpus about 1.2 times length of merus, slenderer than merus, with slender seta distoventrally; propodus slightly shorter and slenderer than carpus, with two widely spaced spiniform setae on ventral margin, in addition to one pair of longer spiniform setae near dactylar base; dactylus about 0.3 times length of propodus, slender, conical, simple, very slightly bending distally ( Fig. 3C, D View FIGURE 3 ). Fourth pereiopod generally similar to third; ischium with one cuspidate seta ( Fig. 3E, F View FIGURE 3 ). Fifth pereiopod somewhat slenderer than fourth pereiopod; ischium unarmed; merus more than 11 times as long as wide, unarmed; carpus noticeably longer and slenderer than merus, with slender seta distoventrally; propodus with two small spaced spiniform setae on ventral margin and one longer spiniform setae adjacent to dactylar base, distal portion of ventrolateral surface with four rows of fairly long serrulate setae forming short cleaning brush; dactylus about 0.3 times length of propodus, similar to that of third and fourth pereiopods ( Fig. 3G, H View FIGURE 3 ).

Second pleopod with appendix masculina as long as appendix interna, furnished with numerous stiff setae distally ( Fig. 1H View FIGURE 1 ). Uropod with lateral lobe of protopod ending in blunt tooth; exopod narrowly ovoid, with small distolateral tooth; diaeresis curved, with blunt subtriangular tooth adjacent to slender spiniform seta; endopod as long as exopod, narrowly ovoid, without specific features ( Fig. 1I View FIGURE 1 ).

Gill formula typical for genus ( Anker 2010a; see also above).

Colouration. Semitranslucent whitish with pale yellow tinge, bright orange gonads visible by virtue of partially transparent carapace ( Fig. 4 View FIGURE 4 ).

Etymology. The new species is named after its collector, a well-known marine biologist and bryozoan expert, Dr. Blanca Figuerola (STRI and Institut de Ciències del Mar, Barcelona); used as a noun in apposition.

Ecology. The holotype was collected under a large piece of coral rock on coarse sand mixed with small fragments of dead corals and shells, at a depth of about 8–10 m.

Remarks. Triacanthoneus blanca sp. nov. is morphologically most similar to T. pacificus , the only other species of the genus present in the eastern Pacific. Most importantly, the two eastern Pacific species share the relative position of the carapacial teeth, the very similar shape and finger-palm proportions of the major chela, as well as the dorsal longitudinal carina on the antennular stylocerite ending in a small, dorsally pointed tooth (see also under T. pacificus below). However, T. blanca sp. nov. is morphologically distinguishable from T. pacificus , for instance, by (1) the presence of three robust setae on the mid-dorsal line of the carapace, just in front of the mid-dorsal tooth (instead of only one in T. pacificus ); (2) the slightly up-turned rostrum; (3) the relatively longer second article of the antennular peduncle; (4) the noticeably broader telson; (5) the slenderer merus and carpus of the minor cheliped; and (6) the slenderer carpus of the major cheliped (cf. Figs. 1–3 View FIGURE 1 View FIGURE 2 View FIGURE 3 and Anker 2010: figs. 5, 6).

The new eastern Pacific species can be easily separated from all western Atlantic congeners, viz. T. toro , T. alacranes , T. chapelianus , T. armatus and T. akumalensis , by (1) the presence of three robust setae on the mid-dorsal line of the carapace; (2) the presence of a sharp tooth at the anterior end of the dorsal lamella of the antennular stylocerite; (3) the major chela palm more robust, more swollen, compared to the slender palms of the four western Atlantic taxa; and (4) the major chela fingers much shorter than the palm (vs. subequal to the palm in A. alacranes or longer than the palm in T. toro , T. chapelianus , T. armatus and especially T. akumalensis ) ( Anker 2010 a, 2010b; Alvarez et al. 2012, 2014). Triacanthoneus blanca sp. nov. differs from both T. chapelianus and T. armatus by the presence of strong lateral carapacial teeth, which are absent in the latter species, and the absence of teeth near or at the post-orbital margin ( Anker 2010b; Alvarez et al. 2014). The relative position of the lateral carapacial teeth also separates T. blanca sp. nov. from T. alacranes , in which these teeth are in a much more posterior position, together with the mid-dorsal tooth ( Anker 2010a). Finally, the length of the rostrum, the position of the ventral rostral tooth, as well as the shape and armature of the major cheliped fingers contribute to distinguish the new species from T. akumalensis , the morphologically and ecologically most distinctive member of the genus (Alvarez et al. 2012).


Florida Museum of Natural History