Harperalpheus leptodactylus, Lazarus, 2017

Lazarus, Juan Felipe, 2017, First finding of the shrimp genus Harperalpheus Felder & Anker, 2007 in the eastern Pacific, with description of a new species from Bahía Málaga, Colombia (Malacostraca: Decapoda: Alpheidae), Zootaxa 4329 (2), pp. 196-200 : 197-199

Harperalpheus leptodactylus sp. nov.

( Fig. 1 )

Type material. Holotype: male (cl 2.45 mm), INV CRU8406 , Colombia, Pacific coast, Bahía Málaga, Mayordomo , 04°01'40.4"N 77°18'38.6"W, intertidal and shallow subtidal mudflat with scarce rocks, depth at low tide: 0–0.5 m, in burrow, suction pump, leg. A. Anker, 24.iv.2009 [field collection number COL-00049].

Description. Small-sized alpheid shrimp (cl of holotype less than 2.5 mm). Body moderately stout, weakly compressed laterally; carapace and pleon glabrous. Anterior margin of carapace forming orbital hood completely covering eyes dorsally and laterally, without orbital teeth ( Fig. 1A, B ). Rostrum subtriangular, broad basally, narrowly produced distally, with acute simple tip, reaching mid-length of second article of antennular peduncle ( Fig. 1A, B ). Pterygostomial angle acutely produced anteriorly ( Fig. 1B ). Cardiac notch well developed.

First to fourth pleura with posterolateral angles rounded to weakly angular, fifth pleuron more angular posterolaterally, sixth pleonite lacking articulated plate at posterolateral angle; sternal surface with preanal plate posteriorly produced into acute median tooth ( Fig. 1C, D ). Telson broken near mid-length, without spiniform setae on remaining dorsal surface ( Fig. 1C ).

Eyes without anteromesial process or tubercle, cornea rather small ( Fig. 1A, B ). Ocellar beak not conspicuous. Epistomial sclerites each with short subacute process.

Antennular peduncle stout, with second article about as long as wide and subequal in length to first, noticeably longer than third; ventromesial carina of first article with sharp anteriorly directed tooth; stylocerite well developed, acute, elongate, reaching beyond distal margin of second article; lateral flagellum biramous, accessory ramus forming short knob, originating at end of second joint, near base of flagellum, bearing at least two tufts of long aesthetascs ( Fig. 1A, B, E ). Antenna with basicerite robust, with stout acute ventrolateral tooth; scaphocerite broadly oval, anterior margin of blade convex, slightly protruding beyond small distolateral tooth; carpocerite broken on both sides (Fig. A, B, F).

Mandible, maxillule, maxilla and first maxilliped not dissected, appearing typical for genus in external view. Second maxilliped with epipod broadened distally, subquadrate, without podobranch ( Fig. 1G ). Third maxilliped pediform, with well-developed flagellum; coxa with lateral plate somewhat produced dorsally, distinctly bilobed distally; antepenultimate article longer and stouter than others, with stiff setae distodorsally; penultimate article almost three times as long as wide proximally, with one long stout seta on ventral suface and several additional stout setae, some elongate, on distoventral margin; ultimate article tapering distally, ending in subacute corneous tip, with minute subapical spiniform seta and long stiff subapical setae; arthrobranch moderately developed ( Fig. 1H ).

Right first pereiopod (cheliped) robust, carried extended or partially flexed below cephalothorax; ischium relatively long, widening distally, with one small spiniform seta distodorsally; merus stout, subtriangular in crosssection, conspicuously widening distally, ventromesial margin with small blunt subtriangular tooth at about midlength; carpus stout, cup-shaped, with apparently only one row of short setae mesially; palm smooth, subcylindrical, longer than fingers, mesial (flexor) surface slightly flattened proximally; fingers bent slightly ventromesially from axis of palm, not gaping when closed, tips curved, crossing distally, cutting edge of pollex with several blunt low teeth on proximal half, cutting edge of dactylus with similar low teeth extending to about 0.6 length of cutting edge ( Fig. 1I –L ). Left first pereiopod missing.

Second, third and fourth pereiopods missing. Fifth pereiopod relatively slender; ischium unarmed; merus about five times as long as wide, armed with one stout spiniform seta, latter situated proximally to meral mid-length; carpus about 0.6 length of merus, armed with slender spiniform seta on distoventral margin; propodus about 2.3 times as long as carpus, with three regularly spaced spiniform setae on ventromesial surface (distal two not visible in lateral view, concealed by cleaning brush) and well-developed cleaning brush consisting of six rows of thick bristle-like setae; dactylus slender, elongate, gradually curving distally, simple, almost half-length of propodus ( Fig. 1M ).

First pleopod with diminutive endopod. Second pleopod with appendix interna slightly overreaching appendix masculina, latter bearing four slender spiniform setae on apex ( Fig. 1N, O ). Uropod with endopod and exopod subequal in length; protopod with lateral lobe ending in single acute tooth; endopod elongate-ovoid, without specific features; exopod with distolateral tooth, diaeresis and adjacent spiniform seta in terminal position; diaeresis poorly developed, restricted to lateral-most portion, with triangular tooth near slender spiniform seta, latter reaching far beyond posterior margin of endopod ( Fig. 1P ).

Gill formula as described for genus ( Felder & Anker 2007).

Colouration in life: whitish with yellowish inner organs visible by partial translucence of carapace; cornea silvery.

Etymology. The new species’ name refers to the slender and long dactylus of the pereiopods, one of the important characters distinguishing it from the type species (see below).

Distribution. Presently known only from the type locality in Bahía Málaga, Pacific coast of Colombia.

Ecology. The single specimen of H. leptodactylus sp. nov. was collected with the aid of suction pump on a shallow intertidal-subtidal mudflat in a small, inland-oriented extension of Bahía Málaga. The burrow host remains unknown. Other infaunal alpheid shrimps collected at this locality include Bermudacaris sp., Automate sp. (Anker, in study), as well as Salmoneus malagensis Anker & Lazarus, 2015 , the latter being associated with extensive burrows of Alpheus colombiensis Wicksten, 1988 ( Anker & Lazarus 2015).

Remarks. Harperalpheus leptodactylus sp. nov. plainly belongs to Harperalpheus , as evidenced by the frontal margin of the carapace with a triangularly produced rostrum and without orbital teeth ( Fig. 1A, B ); the pterygostomial angle of the carapace strongly and sharply produced anteriorly ( Fig. 1B ); the sixth pleonite with a posteriorly elongated sharp preanal plate, but without an articulated flap ( Fig. 1C, D ); the lateral plate on the third maxilliped coxa produced dorsally and bilobed ( Fig. 1H ); the fifth pereiopod merus armed with a stout spiniform seta ( Fig. 1M ); the cheliped carpus furnished with at least one row of short setae mesially ( Fig. 1I ); and the diaeresis and associated structures of the uropodal exopod in a rather unusually terminal position ( Fig. 1P ) (see also Felder & Anker 2007: figs. 1a–d, 2i, 3b, h, 4h).

The new species can be most easily separated from H. pequegnatae by the conspicuously longer slender dactylus of the fifth pereiopod (and presumably also other walking legs, which are missing in the holotype of H. leptodactylus sp. nov.). In H. leptodactylus sp. nov., the dactylus of the fifth pereiopod is nearly half as long as the propodus, whilst in H. pequegnatae , it is barely reaching 1/3 of the propodus length (cf. Fig. 1M and Felder & Anker 2007: fig. 3h). Other important differences include the noticeably stouter antennular peduncle, with the second article as long as wide in H. leptodactylus sp. nov. vs. at least 1.5 times longer than wide in H. pequegnatae ; the much longer stylocerite, reaching well beyond the distal margin of the second article of the antennular peduncle in H. leptodactylus sp. nov. vs. only slightly reaching the mid-length of the second article in H. pequegnatae (cf. Fig. 1A and Felder & Anker 2007: fig. 1b); and the presence of only one setal row on the mesial surface of the cheliped carpus in H. leptodactylus sp. nov. vs. several setal rows in H. pequegnatae (cf. Fig. 1I and Felder & Anker 2007: fig. 3b).

Both species seem to have a small blunt tooth situated at about mid-length of the ventromesial margin of the cheliped merus ( Fig. 1I ). Although the cheliped merus was described as “unarmed” in the description of H. pequegnatae , a minute tooth (or rather a tiny tubercle) can be seen in ventromesial view of the cheliped in Felder & Anker (2007: fig. 3b). However, in H. leptodactylus sp. nov., this tooth appears to be stronger, especially considering the relatively smaller size of the holotype specimen. In general proportions, the cheliped of H. leptodactylus sp. nov. is reminiscent of the cheliped of the smaller paratype of H. pequegnatae illustrated in Felder & Anker (2007: fig. 3d).

The incompleteness of the holotype of H. leptodactylus sp. nov. is certainly a result of the rather violent extraction of this very small shrimp specimen from the burrow, by means of a metallic suction pump, and currently prevents a more detailed knowledge of the external morphology of the new species. In particular, several important features of the second, third and fourth pereiopods, as well as telson and antennal carpocerite, remain unknown. Additional collecting at the type locality will hopefully yield additional specimens that would enable to complete the description of H. leptodactylus sp. nov. and perhaps shed some light on its ecology and presumed association with some burrowing animal.

Harperalpheus is the 15th alpheid genus reported from the eastern Pacific. Among the other 14 genera, Harperalpheus superficially resembles Alpheopsis Coutière, 1897 and Salmoneus Holthuis, 1955 (especially specimens missing major cheliped). However, none of these genera has a strong, anteriorly produced pterygostomial tooth ( Fig. 1B ), although some eastern Pacific species of Alpheopsis have either a minute pterygostomial tooth or a strong non-homologous tooth situated just above the pterygostomial angle, terminating a strong lateral carina ( Anker, 2017). They also lack row of setae on the cheliped carpus, a feature shared by Harperalpheus , Leslibetaeus and a few other relatively “basal” alpheid genera ( Anker et al. 2006b). However, Harperalpheus and Leslibetaeus can be easily separated from each other by the frontal margin of the carapace, which is produced into a strong rostrum in both members of the former genus, and not produced, almost rounded, in both members of the latter genus ( Fig. 1A ; see also Anker et al. 2006a: fig. 2a), as well as some other morphological details. A full key to all eastern Pacific alpheid genera, including an additional as yet unreported genus (Anker, in prep.), will be provided elsewhere.

Figures

FIGURE 1. Harperalpheus leptodactylus sp. nov., holotype, male (cl 2.45 mm), INV CRU 8406, Bahía Málaga, Pacific coast of Colombia: A, frontal region, dorsal view (left scaphocerite and carpocerite missing); B, same (right carpocerite missing), lateral view; C, posterior pleomeres and telson (broken), right uropod removed, lateral view; D, preanal plate of sixth pleomere, ventral view; E, tooth on ventromesial carina of first article of antennular peducle, lateral view; F, right scaphocerite of antenna, ventral view; G, second maxilliped, lateral view; H, third maxilliped, lateral view; I, right cheliped, mesial view; J, same, lateral view; K, same, carpus and chela with fingers closed, mesial view; L, same, carpus and chela with fingers open, mesial view; M, fifth pereiopod, lateral view; N, second pleopod, lateral view; O, same, detail of appendix interna and appendix masculina; P, uropod, dorsal view. Scale bar for A – N as indicated, O drawn without scale.