Salmoneus depressus, Anker, Arthur, 2011

Anker, Arthur, 2011, Two new species of Salmoneus Holthuis, 1955 with a deep dorsal depression on the carapace (Crustacea, Decapoda, Alpheidae), Zootaxa 3041, pp. 39-50 : 44-48

Salmoneus depressus sp. nov.

Figs. 4–6

Jousseaumea trigona (not Rathbun, 1901) – Schmitt 1924: 81.

Type material. Caribbean coast of Panama. Holotype: 1 ovig. specimen (cl 5.4 mm), MNHN-IU-2011-5174, Bocas del Toro, Crawl Cay (Cayo Coral), sand flat with seagrass, rubble, sponges, in fine sand under very large rock, about 1 m, leg. A. Anker, 11.08.2008 [fcn 08-215]. Paratypes: 1 ovig. specimen (cl 4.8 mm), MNHN-IU- 2011-5175, Bocas del Toro, Isla Colón, Punta Caracol, under rocks and rubble on sand, 1–2 m, leg. A. Anker [fcn 07-147B]; 1 ovig. specimen (cl 4.6 mm), MNHN-IU-2011-5176, Bocas del Toro, Isla Colón, Punta Caracol, under rocks and rubble on sand, 1–2 m, leg. A. Anker, 30.03.2008 [fcn 08-002]; 1 ovig. specimen (cl 4.8 mm), MNHN- IU-2011-5177, Bocas del Toro, Crawl Cay (Cayo Coral), sand flat with seagrass, rubble, sponges, near mangroves, about 1 m, leg. A. Anker, 31.03.2008 [fcn 08-007]; 1 non-ovig. specimen (cl 3.5 mm), MNHN-IU-2011-5178, Bocas del Toro, Crawl Cay (Cayo Coral), sand flat with seagrass, rubble, sponges, near mangroves, about 1 m, leg. A. Anker, 11.08.2008 [fcn 08-227]; 2 ovig. specimens (cl 3.8 mm, 4.1 mm), OUMNH.ZC. 2011-06-016, Bocas del Toro, Isla Colón, Boca del Drago, in or under coral rubble, less than 1 m, leg. A. Anker, 0 5.08.2008 [fcn 08-232]; 1 ovig. specimen (cl 3.7 mm), RMNH D53456, Bocas del Toro, Isla Colón, STRI bay, off STRI dock, sand flat with seagrass and rubble, suction pump, about 1 m, leg. A. Anker, B. Martínez-Guerrero, 14.08.2008 [fcn 08-242]; 1 non-ovig. specimen (cl 3.7 mm), RMNH D53457 , Bocas del Toro, Isla Colón, STRI point, sand flat with rubble and seagrass, in empty urchin test, 1.5–2 m, leg. A. Anker, J.A. Vera Caripe, 17.11.2006 [fcn 06-593]; 1 non-ovig. specimen (cl 3.4 mm), OUMNH.ZC. 2011-06-017, Bocas del Toro, east of Isla San Cristobal, Laguna Porras, Sta. 9, 9º16’514”N, 82º14’833”W, loose coral rubble, 7 m, leg. S. De Grave, M. Salazar, 0 2.08.2005 [fcn 08-258].

Additional (non-type) material examined. Caribbean coast of Panama: 1 specimen (cl 4.1 mm), UP, San Blas Islands, small island near Cartí, sand flat with abundant coral rubble, under large pieces of rubble, less than 2 m, leg. A. Anker, 22.05.2007 [fcn 07-180]. Venezuela: 1 non-ovig. specimen (in bad condition) (cl 3.8 mm), UO, northeast of Isla Margarita, Islas de los Frailes, rocky intertidal, leg. J.A. Vera Caripe [fcn 03-012]. Barbados: 1 ovig. specimen (cl 5.0 mm), USNM 68718, University of Iowa Barbados-Antigua Expedition, 29.05.1918, det. W.L. Schmitt as “ Jousseaumea trigona Rathbun ” [now Alpheopsis trigona (Rathbun) ].

Description. Small-sized alpheid shrimp (cl range 3.5–5.4 mm). Rostrum well developed, longer than broad at base, with acute tip, latter usually reaching or slightly exceeding mid-length of second article of antennular peduncle; lateral margins shallowly concave in dorsal view; ventral margin usually with minute notch or tooth subdistally; rostral carina very faint, barely reaching level of eyes ( Fig. 4 A–C). Orbital teeth strong, acute, directed anteriorly ( Fig. 4 A). Pterygostomial angle slightly protruding anteriorly, rounded ( Fig. 4 B). Carapace sparsely covered with setae; dorsal surface with deep, dent-like, narrowly ovoid, longitudinal depression, starting at about 1/3 carapace length (more or less above pterygostomial angle) and ending at some distance from posterior margin of carapace; lateral margins of median depression slightly elevated, appearing as low longitudinal ridges; anterior end of depression sometimes with slight elevation on mid-dorsal line ( Fig. 4 D–F).

Sternum with rounded process between bases of second pereiopods. Pleuron of fifth abdominal somite projecting as small acute tooth; sixth somite without articulated plate, sharply produced posteriorly; preanal plate triangular, bluntly produced posteriorly ( Fig. 4 G, H).

Telson widest in proximal third, distally tapering; dorsal surface with two pairs of stout spiniform setae, inserted at some distance from lateral margin, at about 0.5 and 0.8 telson length, respectively; posterior margin approximately 2/3 length of anterior margin, with U-shaped median incision; two pairs of stout spiniform setae present at posterolateral angles, mesial distinctly longer than lateral; median incision furnished with three pairs of slender, plumose setae ( Fig. 4 I).

Eyes concealed in dorsal and lateral views, with blunt lateral process, latter sometimes visible in lateral view; cornea well developed ( Fig. 4 A, B). Epistomial sclerites with short, blunt processes.

Antennular peduncles stout, with second article slightly longer than wide; stylocerite pressed tightly against peduncle, with subacute tip reaching or almost reaching distal margin of second article; ventromesial carina with strong, anteriorly directed tooth (visible in Fig. 4 B); lateral flagellum biramous, fused portion with three articles, accessory ramus well developed, with at least six groups of aesthetascs ( Fig. 4 A, B). Antenna with basicerite ending in stout distoventral tooth; scaphocerite ovate, with broad, anteriorly rounded blade not reaching beyond tip of stout, sharp distolateral tooth; carpocerite stout, reaching about 3/4 length of scaphocerite ( Fig. 4 B, J).

Mouthparts typical for genus in external view. Third maxilliped as described for previous species.

Chelipeds very unequal in size and asymmetrical in shape; minor cheliped much shorter, more slender, with a much smaller, non-enlarged chela; both chelipeds folded when not in use ( Fig. 5 A, B, D). Major cheliped moderately long and robust; ischium distally widening, unarmed; merus distally widening, flattened ventrolaterally; carpus short, cup-shaped, embracing proximal portion of palm; palm with deep proximo-mesial excavation, both dorsal and ventral surfaces hollowed, forming dent-like, longitudinal excavations; fingers about as long as palm, with tips curved and crossing when closed; cutting edges serrate with about 11–12 mostly subtriangular teeth, most-distal portions of cutting edges without teeth ( Fig. 5 A–C). Minor cheliped with ischium armed with stout setiform seta; merus about four times as long as wide; carpus as long as merus, distally widening; chela simple, with fingers somewhat gaping, slightly shorter than palm; cutting edges smooth ( Fig. 5 D, E).

Second pereiopod slender; ischium usually with spiniform seta, occasionally unarmed; merus longer than ischium; carpus five-articulated, first article being equal to sum of four others, ratio of carpal articles (from proximal to distal) approximately 4.5: 1: 0.8: 1: 2; chela simple, distinctly longer than most-distal carpal article ( Fig. 5 F, G). Third pereiopod moderately slender, compressed; ischium with two or three spiniform setae on ventrolateral surface; merus more than five times as long as wide, unarmed; carpus more slender than merus, about 0.7 merus length, with slender spiniform seta distoventrally; propodus with three slender spiniform setae along ventral margin and one pair of longer spiniform setae on distoventral edge, adjacent to dactylus; dactylus at least half as long as propodus, slender, gradually curving, with some setae at about 0.7 dactylar length ( Fig. 5 H). Fourth pereiopod generally similar to third. Fifth pereiopod somewhat longer and more slender than third and fourth pereiopods; ischium unarmed; merus subequal to carpus; propodus with a few small spiniform setae along ventral margin and two stronger spiniform setae distally, setal brush composed of at least 13 rows of serrulate setae becoming longer distally ( Fig. 5 I).

Second pleopod with appendix masculina not exceeding appendix interna, with row of stiff setae, as illustrated ( Fig. 4 K). Uropod with lateral lobe of protopod bearing sharp tooth; endopod and exopod ovoid; diaeresis slightly sinuous, with small blunt tooth adjacent to stout spiniform seta ( Fig. 4 L). Gill-exopod formula typical for genus (see Anker & Marin 2006).

Colour in life. Whitish to pale yellow, with slight pinkish tinge, especially on antennules, antennae and tail fan; eggs reddish ( Fig. 6 ).

Etymology. From Latin word depressus (depressed, hollowed), referring to the deep depression on the carapace; used as an adjective.

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

Distribution. Presently known from the Caribbean coast of Panama (Bocas del Toro and San Blas Islands), Venezuela (Islas de los Frailes) and Barbados.

Ecology. Shallow subtidal, known depth range 1–7 m; sand flats with relatively fine sand mixed with loose coral rubble, and with large pieces of eroded coral, sometimes near seagrass meadows or mangroves; usually under coral rocks, occasionally also in burrows, empty urchin tests (present study), and empty conch shells ( Schmitt, 1924).

Remarks. Both S. excavatus sp. nov. and S. depressus sp. nov. can be separated from all previously described species of Salmoneus by the presence of a deep, dent-like depression on the mediodorsal surface of the carapace. Salmoneus depressus sp. nov. differs specifically from the above-described S. excavatus sp. nov. by the stronger and more anteriorly directed orbital teeth (cf. Figs 1 A, 4A); the slightly shorter second article of the antennular peduncle (cf. Figs 1 A, 4A); the ischium of the minor cheliped armed with a strong spiniform seta, which is lacking in S. excavatus sp. nov. (cf. Figs. 2 E, 5D); the proximal teeth of the major chela dactylus being subtriangular vs. broad and distally truncate in S. excavatus sp. nov. (cf. Figs. 2 D, 5C); and also by the reddish colour of fresh eggs, which are yellow in S. excavatus sp. nov. (cf. Figs. 3 , 6 ). The presence or absence of a spiniform seta on the ischium of the second pereiopod cannot be used as a character to distinguish the two transisthmian species for its presence appears to be variable in S. depressus sp. nov. ( Fig. 5 F, G).

Figures

FIGURE 1. Salmoneus excavatus sp. nov. A – M, paratype, non-ovigerous specimen (cl 5.3 mm) from Chumical, Pacific coast of Panama, RMNH D 53455; N, O, holotype, ovigerous specimen (cl 4.9 mm) from Chumical, MNHN-IU- 2011 - 5173; A, anterior region of carapace and frontal appendages, dorsal; B, same, lateral; C, same, tip of rostrum; D, carapace, lateral (note: posterior margin covered by pleuron of first abdominal somite); E, same, dorsolateral; F, same, dorsal; G, fifth and sixth abdominal somites, lateral; H, preanal plate of sixth abdominal somite, ventral; I, telson, dorsal (note: abnormal telson with three spiniform setae missing); J, tooth on ventromesial carina of first article of antennular peduncle, lateral; K, antennal scaphocerite, dorsal; L, second pleopod, appendix masculina and appendix interna, mesial; M, uropod, dorsal; N, frontal margin of carapace; O, telson, dorsal (note: typical configuration). Scale bars as indicated; fig. H drawn without scale.

FIGURE 2. Salmoneus excavatus sp. nov. A – I, paratype, non-ovigerous specimen (cl 5.3 mm) from Chumical, Pacific coast of Panama RMNH D 53455; A, third maxilliped, lateral; B, major cheliped, mesial; C, same, lateral; D, major chela, lateral; E, minor cheliped, lateral; F, minor chela, lateral; G, second pereiopod, lateral; H, third pereiopod, lateral; I, fifth pereiopod, lateral. Scale bars as indicated.

FIGURE 3. Salmoneus excavatus sp. nov. A, B, holotype, ovigerous specimen (cl 4.9 mm) from Chumical, Pacific coast of Panama, MNHN-IU- 2011 - 5173, dorsal and lateral; C, paratype, non-ovigerous specimen (cl 5.3 mm) from Chumical, RMNH D 53455, lateral.

FIGURE 4. Salmoneus depressus sp. nov. A – L, paratype, ovigerous specimen (cl 4.8 mm) from Bocas del Toro, Caribbean coast of Panama, MNHN-IU- 2011 - 5175; M, holotype, ovigerous specimen (cl 5.4 mm) from Bocas del Toro, MNHN-IU- 2011 - 5174; A, anterior region of carapace and frontal appendages, dorsal; B, same, lateral; C, same, tip of rostrum; D, carapace, lateral; E, same, dorsolateral; F, same, dorsal; G, fifth and sixth abdominal somites, lateral; H, preanal plate of sixth abdominal somite, ventral; I, telson, dorsal; J, antennal scaphocerite, dorsal; K, second pleopod, appendix masculina and appendix interna, mesial; L, uropod, dorsal; M, frontal margin of carapace. Scale bars as indicated; fig. H drawn without scale.

FIGURE 5. Salmoneus depressus sp. nov. A – I, paratype, ovigerous specimen (cl 4.8 mm) from Bocas del Toro, Caribbean coast of Panama, MNHN-IU- 2011 - 5175; A, major cheliped, mesial; B, same, lateral; C, major chela, lateral; D, minor cheliped, lateral; F, same, carpus and minor chela, mesial; G, second pereiopod, lateral; H, third pereiopod, lateral; I, fifth pereiopod, lateral. Scale bars as indicated.

FIGURE 6. Salmoneus depressus sp. nov. A, B, holotype, ovigerous specimen (cl 5.4 mm) from Bocas del Toro, Caribbean coast of Panama, MNHN- IU- 2011 - 5174, dorsal and lateral; C, paratype, ovigerous specimen (cl 3.7 mm) from Bocas del Toro, RMNH D 53457, lateral.