Alpheopsis trigona Rathbun 1901
Creators: name: Anker, Arthur
Publisher: name: Zenodo
Year: 2017
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Alpheidae
Alpheopsis
Alpheopsis trigona

description: Alpheopsis trigona (Rathbun, 1901)
(Figs. 2–4)
Jousseaumea trigona Rathbun 1901: 111, fig. 21; Schmitt 1924a: 68; Schmitt 1935: 140 (partim, fig. 15 based on Rathbun 1901).
Alpheopsis trigonus — Chace 1972: 56 (partim); Rodriguez 1980: 137; (?) Sterrer 1986: 324, text-pl. 105, pl. 9, fig. 2; (?) Martínez-Iglesias 1986: 5, 11, fig. 4C; (?) Campos 1995: 67; (?) Martínez-Iglesias et al. 1996: 32; (?) Williams et al. 2001: 376; (?) Felder et al. 2009: 1056; (?) Souza et al. 2011: 46; (?) Humann et al. 2013: 105.
Alpheopsis trigona — Soledade et al. 2015: 57, fig. 3A.
Not Alpheopsis trigonus — Chace 1972: 56 (partim, material from Barbuda and Yucatan, = A. paratrigona sp. nov.; see below); Coelho Filho 2006: 7; Alves et al. 2008: 48 (= Alpheopsis sp.).
Not Jousseaumea trigona — Schmitt 1924b: 81; Schmitt 1935: 140 (partim, specimen from Barbados) (= Salmoneus depressus Anker, 2011; see Anker 2011).
Type material. Holotype: female (cl 5.5 mm), USNM 23785, southeast of Puerto Rico, off Vieques Island, U.S. Fish Commission Steamer Fish Hawk sta. 6096, depth: 6 fathoms (= 11 m), coral, 1899.
Additional material examined. 1 male (cl 5.4 mm), USNM 135844, US Virgin Islands, Peter Island, Little Bay, Smithsonian-Bredin Caribbean Expedition sta. 22-58, depth: 1–2 m, 30 March 1958; 1 ovig. female (cl 5.7 mm, missing both chelipeds), USNM 135845, same collection data; 1 female (cl 5.5 mm), MZUSP 34221, USA, Florida, Fort Pierce, Walton Rocks Beach, intertidal, under rocks, coll. J.A. Baeza, September 2007 [fcn 07-302].
Redescription. Medium-sized species of Alpheopsis (present material: maximum cl 5.7 mm). Carapace with one strong MDC extending from rostral tip to almost posterior margin of carapace; each side of carapace with one strong ASC running in parallel and lateral to MDC, starting at almost frontal margin of carapace and abruptly ending at about 0.7 length of carapace, sometimes forming short high crest above eye; one PSC running in parallel and lateral to MDC, starting posterior to ASC, sometimes with anterior end extending ventrolaterally as low CSR; one DLC running slightly obliquely from postorbital area to at least carapace mid-length, sometimes extending posteriorly and almost reaching cardiac notch; one VLC running ventral and in parallel to DLC, starting slightly anterior to DLC and reaching or falling slightly short of carapace mid-length; one short PLC running in parallel and ventrolateral to PSC, from about 0.8 to 0.9 length of carapace length, sometimes obsolete or in continuation with DLC; and one strong ABC running along and somewhat above branchiostegial margin to about 0.2–0.3 carapace length, with stout subacute tooth at anterior end, latter protruding well beyond anterolateral margin (Figs. 2 a–d; 4a, d–g).
Rostrum well developed, up to twice as long as wide at base, with strong dorsal carina, latter sometimes gently sloping shortly before reaching acute tip, latter usually overreaching distal margin of first article of antennular peduncle, sometimes reaching mid-length of second article (Figs. 2 c, d; 4a, f, g). Orbital hoods broadly rounded anteriorly, not protruding anteriorly as orbital teeth (Figs. 2 c, d; 4f, g). Pterygostomial angle below strong tooth of ABC broadly rounded (Figs. 2 a, c; 4a, d, f).
First and second pleomeres with strong MDC-PL1 and relatively low MDC-PL2, respectively, continuing MDC of carapace; third to sixth pleomeres unarmed dorsally; all pleura rounded ventrally; fifth pleuron with posteroventral angle rounded; sixth somite with bluntly projecting posterior lobe and well-delimited, triangular, articulated plate (Figs. 2 a, b, e; 4d, e). Telson moderately broad, tapering distally, about 2.5 as long as anterior width; dorsal surface with median longitudinal depression and typically with two pairs of stout spiniform setae inserted at some distance from lateral margin, at about 0.5 and 0.75 telson length, respectively; posterior margin about half as long as anterior margin, broadly rounded; each posterolateral angle with one pair of stout spiniform setae, mesial much longer than lateral (Fig. 2 f, note: telson of this specimen with posterior spiniform setae broken off and also untypically missing one of dorsal spiniform setae).
Eyes completely concealed by orbital hoods, not visible in dorsal and lateral view; eyestalk with wellpigmented cornea (Fig. 2 c, d). Epistomial sclerite each with strong sharp process.
Antennular peduncles stout; stylocerite strong, with sharp tip, latter overreaching distal margin of second article; ventromesial carina with anteriorly directed, acute tooth; second article about 1.2–1.4 times as long as wide; lateral flagellum biramous; fused portion short, with four or so joints; accessory ramus long, with several groups of long aesthetascs (Figs. 2 c, d, g; 4f, g). Antenna with basicerite ending in sharp tooth distoventrally; scaphocerite ovate, with anteriorly rounded blade and sharp distolateral tooth, latter not reaching beyond anterior margin of blade; anterior margin of scaphocerite exceeding distal margin of antennular peduncles; carpocerite reaching to end of scaphocerite (Figs. 2 c, d; 3f, g).
Mouthparts typical for genus in external view. Third maxilliped slender, pediform; coxa with distally subacute lateral plate above mastigobranch; penultimate article about 2.5 times as long as wide proximally; ultimate article tapering to slender corneous tip, with one stiff subdistal spiniform seta mesiodorsally; arthrobranch well developed (Fig. 2 h, i).
Chelipeds subequal or slightly unequal in size, asymmetrical in shape and armature on finger cutting edges (at least in adult males), carried extended when not in use (Figs. 3 a–d; 4b, c, h–k). Ischium stout, short, with stout spiniform seta distodorsally (Fig. 3 a, b; 4b, h, j). Merus almost as long as wide in adult males, noticeably slenderer, much longer than wide in females, broadening distally, distinctly triangular in cross-section, with three welldefined margins, dorsal margin ending in very conspicuous blunt tooth, proximodorsal margin sometimes with small spiniform seta (Fig. 3 a, b; 4b, h, j). Carpus very stout, short, cup-shaped, widening distally, with strong dorsal constriction, ventral margin typically with one very stiff seta (Figs. 3 a–c; 4b, c, h–k). Male major chela robust, with palm conspicuously flattened on mesial surface and fingers about 0.6 length of palm; dorsomesial-proximal surface of palm with strong, usually somewhat dorsally and/or anteriorly projecting, distally curved process; fingers conspicuously gaping, strongly crossing distally; cutting edges of fingers with few strong, rounded or subtriangular teeth, two on dactylus and three on pollex, distal-most teeth very large, especially on pollex; adhesive disks feebly developed (Fig. 4 h, i). Male minor chela with palm flattened on mesial surface and fingers about 0.9 length of palm; dorsomesial-proximal surface of palm with strong, dorsally and/or anteriorly projecting, distally curved process, latter similar to that of major chela; dactylus somewhat flattened dorsally; cutting edges of fingers unarmed or finely and irregularly dentate, usually with row of short setae parallel to cutting edge (Fig. 4 j, k). Female minor chela generally similar to male minor chela, less robust, with slenderer fingers; dorsomesialproximal surface of palm with moderately to strongly projecting, usually distally curved process; cutting edges of fingers unarmed or armed with small irregular teeth (Figs. 3 a–d; 4b, c).
Second pereiopod moderately slender; ischium subequal to merus in length; carpus with five joints; ratio of carpal joints (from proximal to distal) approximately equal to: 4: 1.2: 1.2: 1: 2.5 (specimen from Florida) or 3: 1.2: 1: 1: 1.9 (specimen from Peter Island); chela longer than distal carpal article, with fingers equal to palm in length, simple (Figs. 3 e; 4l). Third pereiopod relatively slender; ischium with one small spiniform setae on ventrolateral surface; merus about 5.3 times as long as wide, unarmed; carpus about 0.6 length of merus, much slenderer, with small spiniform seta on distoventral margin; propodus with three spiniform setae along ventral margin and pair of distal spiniform setae adjacent to dactylus; dactylus about 0.4 length of propodus, slender, simple, conical, gradually curving distally (Figs. 3 f, g; 4m). Fourth pereiopod very similar to third pereiopod. Fifth pereiopod more slender than third and fourth pereiopods; ischium unarmed on ventrolateral surface; merus about six times as long as wide, unarmed; carpus about 0.7 length of merus; propodus long, slender, with four or so spiniform setae along ventral margin, one long distal spiniform setae adjacent to dactylus, and few rows of serrulate setae on distolateral surface; dactylus about 0.4 length of propodus, similar to that of third pereiopod (Fig. 3 h).
Male second pleopod with appendix masculina well developed, as long or slightly exceeding appendix interna; apex of appendix masculina with several long stiff setae. Uropod with lateral lobe of protopod ending in long sharp tooth; endopod and exopod broadly ovate; exopod with distolateral tooth and adjacent spiniform seta both strong; diaeresis with distinct subtriangular tooth adjacent to spiniform seta and sinuous mesial portion (Fig. 2 j).
Gill-exopod formula: five pleurobranchs above first to fifth pereiopods; five mastigobranchs on coxae of third maxilliped and first to fourth pereiopods; five setobranchs on coxae of first to fifth pereiopods; one arthrobranch at base of third maxilliped; no podobranchs; three exopods on first to third maxilliped.
Colour pattern. Background semitransparent whitish; carapace covered with bright red chromatophores, except for anterior-most dorsal and posterior-most lateral portions; pleon with three transverse bands of red chromatophores, one anterior band across first pleomere and diffusely extending to second pleomere laterally, and two adjacent posterior bands across most of third and fourth pleomeres; antennular and antennal flagella pale yellow-orange; chelipeds hyaline white; walking legs and tail fan whitish (based on photograph in Soledade et al. 2015: fig. 3A).
Type locality. Off Vieques Island, southeast of Puerto Rico.
Distribution. Western Atlantic: confirmed only from Puerto Rico (Vieques Island, type locality); U.S. Virgin Islands (Peter Island); Florida (Fort Pierce); and Brazil: Bahia (Abrolhos Archipelago) (Rathbun 1901; Schmitt 1924a, 1935; Chace 1972; Soledade et al. 2015; present study). Records from Bermuda (Sterrer 1986); southern Gulf of Mexico (Felder et al. 2009); Curaçao (Schmitt 1924a); Colombia (Santa Marta, Campos 1995); Panama (San Blas Islands, Williams et al. 2001); Cuba (Gulf of Batabano, Martínez-Iglesias 1986; Martínez-Iglesias et al. 1996) will require confirmation as at least some of them may refer to the closely related A. paratrigona sp. nov., which occurs from Bermuda to the southern Caribbean Sea (see below). For the same reason, the identity of shrimps identified as A. trigona on colour photographs in Sterrer (1986) and Humann et al. (2003) also remains uncertain.
Ecology. Coral reefs and associated habitats rich in coral rubble, also on rocky-sandy mixed bottoms and among nodules of coralline algae; in crevices of dead corals, under rocks and coral rubble, in empty conch shells, Lobatus gigas (L.); intertidal to at least 30 m (Chace 1972; present study).
Remarks. Alpheopsis trigona appears to be widespread in the subtropical and tropical areas of the western Atlantic, although the only presently confirmed records of A. trigona are from southern Florida (Fort Pierce), two localities in the Caribbean Sea (Puerto Rico, U.S. Virgin Islands), and the Brazilian state of Bahia (see below). The material from Bermuda and several Caribbean localities (Guadeloupe, Belize, Barbuda), including some of the material reported as A. trigona by Chace (1972), is here assigned to A. paratrigona sp. nov. (see below).
The species appears to be variable in the development of some carinae of the carapace and also in the cheliped armature and length ratio in the second pereiopod carpus. For instance, in the female holotype and in the male from Peter Island, DLC extends to about 0.6 length and past 0.8 length of the carapace, respectively (Fig. 4 a, d, e), whereas in the female from Florida, DLC is much shorter, reaching only slightly beyond carapace mid-length, although a short PLC present in the posterior third of the carapace may be seen as a posterior continuation of DLC (Fig. 2 a, b). The cheliped fingers may be unarmed, as in the female holotype (Fig. 4 b), or armed with stout teeth as in the major cheliped of the male from Peter Island (Fig 4 i), although this may be due to cheliped asymmetry. The second pereiopod of the female from Florida is noticeably more slender compared to that of the male from Peter Island, with the first article being relatively longer (cf. Figs. 3 e; 4l). These and some other minor differences are here seen as intraspecific variation until more evidence is available (comparison of DNA, additional material).
Coelho Filho (2006) reported A. trigona (as A. trigonus) from several offshore localities in northeastern Brazil (Ceará, Fernando de Noronha Chain off Pernambuco, Paraíba), with material deposited in the carcinological collection of the Departamento de Oceanografia, Universidade Federal de Pernambuco, Recife, Brazil (DOUFPE). At the author’s request, Jesser Fidelis (DOUFPE) examined this material and confirmed that it does not belong to A. trigona as none of the specimens had a strong mid-dorsal carina or any other carinae on the carapace. Therefore, Coelho Filho’s (2006) record, which was merely repeated in the checklist of Alves et al. (2008), should be provisionary treated under “ Alpheopsis sp.” until more evidence is available.
More recently, Soledade et al. (2015) reported a single female of A. trigona collected in the intertidal of Ilha de Sánta Barbara in the Abrolhos Archipelago off Bahia, Brazil. This specimen was described as having “nine sharp longitudinal or oblique crests”, which matches the configuration found in the holotype (Fig. 4 a) and the specimen from Peter Island (Fig. 4 d, e). This record proves that A. trigona definitively occurs in Brazil, as far south as Bahia, although the exact distribution of the species in the southwestern Atlantic remains unknown.
description: Published as part of Anker, Arthur, 2017, Strongly carinate species of Alpheopsis Coutière, 1897 of the tropical Atlantic and eastern Pacific, with redescription of A. trigona (Rathbun, 1901) and description of three new species (Malacostraca: Decapoda: Alpheidae), pp. 199-227 in Zootaxa 4277 (2) on pages 201-206, DOI: 10.11646/zootaxa.4277.2.2, http://zenodo.org/record/809634