Triacanthoneus pacificus Anker, 2010, n. sp.
Creators: name: Anker, Arthur
Publisher: name: Zenodo
Year: 2010
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Alpheidae
Triacanthoneus
Triacanthoneus pacificus

description: Triacanthoneus pacificus n. sp.
(Figs. 5, 6, 10 D–F)
Type material. Holotype: ovigerous female (CL 2.8 mm), USNM 1145374, Panama, Pacific coast, Playa Venao, intertidal, exposed at low tide, under rocks in sand, coll. J.A. Baeza (processed by A. Anker), 18 March 2007, fcn 07-090.
Additional material examined. 2 ovigerous females (CL 2.9, 3.4 mm), UVC, Colombia, Pacific coast, Bahía Malaga, Los Negros, sand-rock bottom, depth 2 m, ARMS (large plastic basket with shells), 25 April 2009, coll. J.F. Lazarus-Agudelo et al. (processed by A. Anker), fcn COL-00135, COL-00136.
Description. Small-sized alpheid shrimp. Carapace with one strong sharp mediodorsal tooth situated distinctly posterior to carapace mid-length and two strong sharp dorsolateral teeth situated ventral and anterior to mediodorsal tooth, in post-hepatic area; stiff seta present on mid-dorsal line anterior to mediodorsal tooth (Fig. 5 B, C). Rostrum straight, more than 1.7 times as long as broad at base; lateral margins slightly concave; tip overreaching mid-length of second segment of antennular peduncle; ventral margin with strong, anteroventrally directed subapical dent; rostral carina well developed, reaching posteriorly to mediodorsal tooth, with one stiff seta approximately at carapace mid-length; orbital teeth obscure, present as small bumps lateral to eye (Fig. 5 A–E). Pterygostomial angle not protruding anteriorly, broadly rounded (Fig. 5 B).
Pleura of first to fourth abdominal somites rounded posteroventrally; fifth pleuron with posteroventral angle subacute. Telson narrow, almost four 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 0.75 telson length, respectively; posterior margin straight, each posterolateral angle with two pairs of spiniform setae, lateral being 0.7 times as long as mesial, and two long plumose setae between mesial spiniform setae (Fig. 5 J).
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. 5 A, B).
Antennular peduncle stout, with second segment distinctly longer than wide; first segment with distally acute stylocerite reaching to 0.4–0.5 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. 5 A, B). Antenna with stout basicerite bearing sharp distoventral tooth; scaphocerite reaching or almost 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. 5 A, B).
Mouthparts not dissected, appearing typical for genus in external view. 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 5 F).
Chelipeds very unequal in size and asymmetrical in shape, carried folded (Fig. 6 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 much shorter than merus, subcylindrical, distally broadening, smooth; chela subcylindrical, smooth; fingers shorter than palm, compressed, cutting edges evenly serrated, with around 10 subtriangular teeth (Fig. 6 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 shorter than merus, subcylindrical, slightly widening distally, smooth; chela simple, smooth, with fingers longer than palm, finger cutting edges straight (Fig. 6 D, E).
Second pereiopod slender; ischium as long as merus, with three spiniform setae on ventrolateral surface; carpus five-segmented, first segment longest, as long as sum of four other segments, ratio of carpal segments (from proximal to distal) more or less equal to: 6: 1.5: 1: 1.5: 2; chela simple, longer than most-distal carpal article (Fig. 6 F, G). Third pereiopod very slender, compressed; ischium elongate, with two spaced spiniform setae on ventrolateral surface; merus elongate, about 10 times as long as wide, smooth; carpus as long as merus; propodus with two slender spiniform setae on ventral margin and one stouter and longer distal spiniform seta adjacent to dactylus; dactylus about 0.45 propodus length, simple, conical, very slender, gradually curving distally, furnished with setae on dorsal margin (Fig. 6 H, I). Fourth pereiopod almost identical to third pereiopod. Fifth pereiopod longer and more slender than third or fourth pereiopods; ischium unarmed; carpus slightly longer than merus, propodus with one small spiniform seta on ventral margin and at least five rows of slender serrulate setae on distolateral surface, most-distal row with longest setae reaching well beyond dactylar base (Fig. 6 J, K).
Second pleopod (of both ovigerous specimens) with appendix interna and appendix masculina, latter exceeding than appendix interna, with stiff apical and subapical setae (Fig. 5 G). 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. 5 H, I).
Gill-exopod formula as described for genus (see above).
Colour in life semitransparent-white, sometimes with pale orange tinge; gonads or eggs yellow-orange (Fig. 10 D–F).
Etymology. Name refers to the Pacific Ocean; the two other species of the new genus are confined to the Atlantic Ocean.
Habitat. The Panamanian type specimen was collected in the mixed sand-mud-rock intertidal at low tide, on sand under large rocks; the Colombian specimen was extracted from an improvised ARMS (large basket with shells) placed on a rock-sand bottom at about 2 m.
Type locality. Playa Venao, Pacific coast of Panama.
Distribution. Presently known only from Playa Venao, Panama, and Bahía Malaga, Colombia, in the tropical Eastern Pacific.
Remarks. Triacanthoneus pacificus n. sp. differs from T. toro n. sp. and T. alacranes n. sp. by the distinctly more robust major chela; and the more ventrally directed subapical dent on the ventral margin of the rostrum; specifically from T. toro n. sp. by the more posterior position of the mediodorsal tooth on the carapace. It specifically differs from T. alacranes n. sp. by the absence of orbital teeth, the more anterior position of the dorsolateral teeth of the carapace, and several other features (see under T. alacranes n. sp. below).
description: Published as part of Anker, Arthur, 2010, A new genus and three new species of alpheid shrimps (Crustacea, Decapoda, Caridea) from the tropical American coasts, pp. 47-63 in Zootaxa 2652 on pages 54-55, DOI: 10.5281/zenodo.198863