Leptalpheus penicillatus, 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 : 12-15

Leptalpheus penicillatus sp. nov.

Figs. 8–10

Type material. Holotype: male (cl 2.8 mm), MNHN-IU-2011-5241, Panama, Pacific coast, Chame Bay, low tide, in perforated mangrove wood, together with Upogebia sp., leg. A. Anker, J.A. Vera Caripe, 0 7.11.2006 [fcn 06- 523].

Additional material. 1 male (cl 2.2 mm), LACM A5486 (ex-AHF 1940-4), Costa Rica, Playa Tarcoles, shore, leg. R.C. Brusca, 22.02.1980.

Description. Frontal margin of carapace broadly rounded, without rostral projection, without orbital crests ( Fig. 8 A, B). Telson widest in proximal third, distinctly tapering distally; dorsal surface with two pairs of strong spiniform setae inserted in deep pits not far from lateral margin; posterior margin rounded, with two pairs of spiniform setae at posterolateral angles, lateral much more slender and shorter than mesial ( Fig. 8 C).

Eyestalks with anteromesial margin rounded. Antennular peduncles moderately stout, not greatly flattened dorsoventrally; stylocerite somewhat appressed, not exceeding distal margin of first article; ventromesial carina with strong tooth ending in small acute point and large rounded convexity, latter reaching beyond acute point; second article slightly longer than wide; lateral flagellum with short secondary ramus ( Fig. 8 A, B, D). Antenna with basicerite not particularly stout, with distoventral tooth; scaphocerite ovate, with broad, subacute distolateral tooth reaching well beyond anterior margin of blade; carpocerite stout, reaching far beyond scaphocerite and slightly beyond end of antennular peduncle ( Fig. 8 B, E). Mouthparts not dissected, typical for genus in external view. Third maxilliped with slightly elongate, distally subacute lateral plate on coxa ( Fig. 8 F).

Major cheliped slender; ischium with small distal process on mesial face; merus slender, depressed ventrally, with lateral and dorsal margins smooth, mesial margin somewhat rugose proximally; carpus cup-shaped, with two blunt processes distoventrally; chela slender, with palm depressed ventrally, mostly smooth, except for small tubercles and rugosities on ventral side; fingers about half palm length, somewhat twisted laterally, only slightly curved, gaping when closed; cutting edge of dactylus armed with several strong, subtriangular teeth, most-proximal largest; cutting edge of pollex armed with teeth, latter somewhat irregular in shape, and with large hiatus and small lateral tooth proximally; dorsomesial surface of dactylus with dense brush of long, fine, flexible setae; adhesive disks absent ( Fig. 9 A–E). Minor cheliped with ischium unarmed; merus slender, ventrally flattened, with smooth margins; carpus very short, cup-shaped; chela slender, simple, with fingers at least 1.5 times as long as palm, tips crossing distally; cutting edge of dactylus armed with at least seven minute teeth ( Fig. 9 F, G).

Second pereiopod with merus distinctly shorter than carpus; carpus four-articulated, with article ratio approximately equal to 4: 1: 1: 2 ( Fig. 8 G). Third and fourth pereiopods similar; third pereiopod relatively stout, compressed; ischium with small spiniform seta on ventrolateral surface; merus at most 3.5 times as long as wide; carpus less than 0.4 length of merus, with slender distoventral spiniform seta; propodus with three slender spiniform setae along ventral margin; dactylus about 0.4 length of propodus, conical, slender, acute distally ( Fig. 8 H). Fifth pereiopod slender, not compressed, with three distal rows of setae on propodus.

Male second pleopod with slender appendix masculina almost twice as long as appendix interna, with three stiff setae on apex ( Fig. 8 I). Uropod with lateral lobe of protopod ending in two small, widely spaced teeth; exopod with slightly truncate margin; diaeresis with blunt tooth laterally, adjacent to stout spiniform seta, and with two subtriangular teeth fringing deep mesial incision ( Fig. 8 J).

Size. The present specimens range from 2.2 to 2.8 mm cl, the largest being the holotype.

Colour in life. Semitransparent with large red chromatophores grouped in larger patches, latter arranged in longitudinal bands; antennular and antennal peduncles and tail fan with numerous red chromatophores; cheliped merus reddish, carpus and chelae colourless; walking legs also colourless ( Fig. 10 ).

Etymology. Referring to the presence of a dense brush of long, fine setae on the dactylus of the major chela (penicillatus—Latin for bearing a brush); used as an adjective.

Type locality. Panama, Pacific coast, Chame Bay.

Distribution. Eastern Pacific: presently known only from the type locality in Panama.

Ecology. The Panamanian holotype specimen was extracted from a hole in mangrove wood partly submerged in mud, adjacent to mangroves fringing a large estuarine mudflat. Two species of Upogebia were also found in this microhabitat, viz. U. maccraryae Williams, 1986 and U. veleronis Williams, 1993 , the latter was the more common species (hosts identified by P. C. Dworschak). The field notes for the Costa Rican specimen are obviously incomplete (“shore”).

Remarks. Leptalpheus penicillatus sp. nov. is closely related to the western Atlantic L. felderi , but can be distinguished from that species by the absence of small frontal crests on the carapace (present in L. felderi ); the cutting edges of the minor chela fingers with only a few teeth (vs. with conspicuous, posteriorly directed teeth on the pollex in L. felderi ); and the shorter carpus of the second pereiopod (cf. Figs. 8 , 9 and Anker et al. 2006, figs. 1–5). Leptalpheus penicillatus sp. nov. is more distantly related to L. pierrenoeli , from which it may be separated by the four-articulated carpus of the second pereiopod (five-articulated in L. pierrenoeli ), the ischium of the third and fourth pereiopods armed with a spiniform seta (unarmed in L. pierrenoeli ), and the presence of a dense setal brush on the dactylus of the major cheliped (absent in L. pierrenoeli ) (cf. Figs. 8 , 9 and Anker 2008, figs. 1, 2).

The holotype of L. penicillatus sp. nov. appears to be a relatively young male, but with a well-developed appendix masculina and adult-like major cheliped, it presents all the features necessary to recognise this species. It is also possible that L. penicillatus sp. nov. represents another small-sized species (of about the same size as L. azuero sp. nov. and L. mexicanus , see above); in fact, the Costa Rican specimen is even smaller than the holotype. Additional sampling of infaunal shrimps on the Pacific coast of Panama and Costa Roca is necessary to determine the maximum size of L. penicillatus sp. nov. and to precise the host or hosts for this and other species of Leptalpheus .

Figures

FIGURE 8. Leptalpheus penicillatus sp. nov., holotype, male from Chame Bay, Pacific coast of Panama (MNHN-IU- 2011 - 5241): 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, scaphocerite, dorsal view; F, third maxilliped, lateral view; G, second pereiopod, lateral view; H, third pereiopod, lateral view; I, appendix masculina and appendix interna, dorsal view; J, uropod, dorsal view (setae omitted).

FIGURE 9. Leptalpheus penicillatus sp. nov., holotype, male from Chame Bay, Pacific coast of Panama (MNHN-IU- 2011 - 5241): A, major cheliped, mesial view; B, same, lateral view; C, same, ischium and proximal portion of merus, mesial view; D, same, carpus and chela, mesial view; E, major chela fingers, lateral view; F, minor cheliped, lateral view; G, same, carpus and chela, mesial view.

FIGURE 10. Leptalpheus penicillatus sp. nov., holotype, male from Chame Bay, Pacific coast of Panama (MNHN-IU- 2011 - 5241), lateral (A) and dorsal (B) views.