Leptalpheus bicristatus, Anker, Arthur, 2011

Anker, Arthur, 2011, Six new species and three new records of infaunal alpheid shrimps from the genera Leptalpheus Williams, 1965 and Fenneralpheus Felder & Manning, 1986 (Crustacea, Decapoda), Zootaxa 3041, pp. 1-38 : 19-23

Leptalpheus bicristatus sp. nov.

Figs. 15–17

Type material. Holotype: male (cl 4.3 mm), MNHN-IU-2011-5243, Panama, Pacific coast, Chame Bay, estuarine mudflat with fringing mangroves, low tide, in perforated mangrove wood, together with Upogebia spp., leg. A. Anker, J.A. Vera Caripe, 0 7.11.2006 [fcn 06-524].

Description. Frontal margin of carapace with broadly triangular rostral projection, with two small orbital crests situated above each eye ( Fig. 15 A, B). Telson widest in proximal third, distinctly tapering distally; dorsal surface with two pairs of strong spiniform setae inserted in deep pits at some distance from lateral margin; posterior margin rounded, with two pairs of spiniform setae at posterolateral angles, lateral much more slender and shorter than mesial ( Fig. 15 C).

Eyestalks with anteromesial margin rounded, slightly protruding ( Fig. 15 B). Antennular peduncles moderately stout, somewhat flattened dorsoventrally; stylocerite appressed, not exceeding distal margin of first article; ventromesial carina with tooth ending in small acute point and large rounded convexity, latter not reaching beyond acute point; second article more than 1.5 times longer than wide; lateral flagellum with short secondary ramus ( Fig. 15 A, B, D). Antenna with stout basicerite ending in large distoventral tooth, dorsal surface somewhat projecting, forming short tooth; scaphocerite oval, with strong subacute distolateral tooth reaching well beyond anterior margin of blade; carpocerite stout, reaching far beyond scaphocerite, but not much beyond end of antennular peduncle ( Fig. 15 A, B). Mouthparts not dissected, typical for genus in external view. Third maxilliped with lateral plate on coxa elongate, distally subacute, reaching slightly beyond arthrobranch ( Fig. 15 E).

Major cheliped not particularly slender, rather robust; ischium with row of tubercles, most-distal larger and reminiscent of distomesial process; merus slender, slightly curved and twisted, depressed ventrally, with lateral and dorsal margins carrying widely spaced, small, rounded tubercles, dorsal surface mostly smooth; carpus short, cupshaped, without distoventral processes; chela somewhat elongate, stout, with palm depressed ventrally, covered with small tubercles on ventral side, many arranged in longitudinal rows; fingers about half palm length, slightly twisted laterally, strongly curved and largely gaping when closed, forceps-shaped; cutting edge of dactylus with one small proximal tooth and one much stronger, subtriangular tooth more distally, distal portion somewhat broadened and shallowly excavated, tip acute; cutting edge of pollex with large, somewhat square-shaped proximal tooth mesially and one large subtriangular tooth laterally, distal portion distinctly broadened and shallowly excavated, tip blunt and somewhat rugose; dactylar tooth fitting into large hiatus between two pollex teeth; adhesive disks absent ( Fig. 16 A–E). Minor cheliped with ischium unarmed; merus moderately slender, ventrally flattened, with smooth margins; carpus very short, cup-shaped; chela not particularly slender or stout, simple, with fingers slightly longer than palm, tips crossing distally; cutting edges of dactylus and pollex armed with widely spaced, small teeth, those of pollex being somewhat larger, especially a conspicuously large tooth at about 0.6 length of pollex ( Fig. 16 F, G).

Second pereiopod with merus slightly shorter than carpus; carpus five-articulated, with article ratio approximately equal to 4: 1: 1: 1: 2 ( Fig. 15 F). Third and fourth pereiopods similar; third pereiopod relatively stout, compressed; ischium unarmed; merus about 3.2 times as long as wide; carpus slightly more than 0.4 length of merus, with distoventral spiniform seta; propodus with three slender spiniform setae along ventral margin; dactylus about half length of propodus, conical, slender, acute distally ( Fig. 15 G). Fifth pereiopod slender, not compressed; propodus with five setal rows distolaterally.

Male second pleopod with slender appendix masculina by far exceeding appendix interna, with six stiff setae, mostly on apex ( Fig. 15 H). Uropod with lateral lobe of protopod ending in two small, widely spaced teeth; exopod with somewhat truncate margin; diaeresis with straight lateral portion, deep mesial incision and large subtriangular tooth near mesial margin ( Fig. 15 I).

Size. The cl of the holotype is 4.3 mm.

Colour in life. Semitransparent with bluish tinge, speckled with reddish or purplish chromatophores arranged in diffuse bands on the abdomen and posterior carapace; antennular and antennal peduncles, chelipeds, and tail fan pale bluish with red chromatophores; walking legs mostly colourless ( Fig. 17 ).

Etymology. Combination of the Latin words bi (two) and cristatus (crested), referring to the two small orbital crests; used as an adjective.

Type locality. Panama, Pacific coast, Chame Bay.

Distribution. Eastern Pacific: presently known only from the type locality on the Pacific coast of Panama.

Ecology. The holotype of L. bicristatus sp. nov. was found at the same site as the holotype of the abovedescribed L. penicillatus sp. nov.: both specimens were extracted from holes in mangrove wood on a large estuarine mudflat, together with two upogebiid mudshrimps, U. maccraryae and U. veleronis .

Remarks. Leptalpheus bicristatus sp. nov. is closely related to L. mexicanus originally described from Baja California, Mexico ( Ríos & Carvacho 1983), and later reported from Colombia ( Ramos 1995; Lazarus-Agudelo & & Cantera-Kintz 2007), from which it can be distinguished by the presence of two small crests on the carapace, right above each eye ( Fig. 15 A, B). In L. bicristatus sp. nov., the orbital crests occupy almost the same position as in L. felderi (cf. Anker et al. 2006, fig. 1A), being much more posterior that the marginal crests of the abovedescribed L. marginalis sp. nov. ( Fig. 1 A–C). These crests are fairly prominent and it is very unlikely that they were overlooked by both Ríos & Carvacho (1983) and Ramos (1995). In addition, a topotypical specimen of L. mexicanus (MNHN-Na 13624) examined in 2001 did not have these crests (A. Anker, pers. obs.).

The major cheliped of L. bicristatus sp. nov. appears to be somewhat stouter than in L. mexicanus , but is otherwise very similar, including the peculiar shape and armature of the chela fingers (cf. Fig. 16 C, E and Ríos & Carvacho 1983, fig. 1a–e). On the other hand, the rostral projection of L. bicristatus sp. nov. is less produced and somewhat blunter than in L. mexicanus , whilst the anterior margin of the scaphocerite blade appears to be less convex in L. bicristatus sp. nov. than in L. mexicanus (cf. Fig. 15 A and Ríos & Carvacho 1983, fig. 1f). In the second pereiopod, the first carpal article is relatively longer in L. bicristatus sp. nov. compared to that in L. mexicanus (cf. Fig. 15 F and Ríos & Carvacho 1983, fig. 2c). A further difference between the two species lies in the shape of the lateral lobe of the uropodal protopod, which has two small teeth separated by a shallowly concave distal margin in L. bicristatus sp. nov. vs. two much stronger teeth separated by a deeply triangular notch in L. mexicanus (cf. Fig. 15 I and Ríos & Carvacho 1983, fig. 1e). The difference in size is rather insignificant: the largest specimen of L. mexicanus was 3.54 mm cl ( Ríos & Carvacho 1983), while the holotype of L. bicristatus sp. nov. is only slightly larger, at cl 4.3 mm. A genetic comparison between L. mexicanus from the Gulf of California and L. bicristatus sp. nov. from Panama is desirable to corroborate the validity of the new species.

Figures

FIGURE 1. Leptalpheus marginalis sp. nov.: all except I—holotype, male from Ciénaga Porto Nao, Caribbean coast of Colombia (USNM 1155316); I—paratype, male from the same locality (USNM 1155317): A, frontal region, dorsal view; B, same, lateral view; C, same detail of anterolateral margin and orbital crests; D, telson, dorsal view; E, ventromesial tooth on first article of antennular peduncle, lateral view; F, lateral antennular flagellum, lateral view; G, scaphocerite, dorsal view; H, antennal flagellum, lateral view; I, third maxilliped, lateral view; J, second pereiopod, lateral view; K, third pereiopod, lateral view; L, appendix masculina and appendix interna, dorsal view; M, uropod, dorsal view (setae omitted).

FIGURE 15. Leptalpheus bicristatus sp. nov., holotype, male from Chame Bay, Pacific coast of Panama (MNHN-IU- 2011 - 5243): A, frontal region, dorsal view; B, same, lateral view; C, telson, dorsal view; D, ventromesial tooth on first article of antennular peduncle, lateral view; E, third maxilliped, lateral view; F, second pereiopod, lateral view; G, third pereiopod, lateral view; H, appendix masculina and appendix interna, dorsal view; I, uropod, dorsal view (setae omitted).

FIGURE 16. Leptalpheus bicristatus sp. nov., holotype, male from Chame Bay, Pacific coast of Panama (MNHN-IU- 2011 - 5243): A, major cheliped in situ, ventral view; B, same, carpus and chela, mesial view; C, same, distal merus, carpus and chela, lateral view; D, same, ischium, mesial view; E, major chela fingers, mesial view; F, minor cheliped, lateral view; G, same, chela, mesial view.

FIGURE 17. Leptalpheus bicristatus sp. nov., holotype, male from Chame Bay, Pacific coast of Panama (MNHN-IU- 2011 - 5243): A – C, lateral views (A, right, B, C, left on different backgrounds); D, dorsal view.