Pachelpheus, Anker, 2020

Anker, Arthur, 2020, A remarkable burrow-dwelling alpheid shrimp, new genus and new species, from the tropical eastern Pacific (Malacostraca: Decapoda: Caridea), Zootaxa 4731 (1), pp. 75-88 : 76-78

Pachelpheus gen. nov.

Diagnosis. Body moderately slender, slightly compressed. Carapace smooth, unarmed; frontal margin with broadly rounded rostral projection, without orbital teeth; pterygostomial angle rounded, slightly produced anteriorly; cardiac notch well developed. First to fifth pleonites rounded posteroventrally; sixth pleonite with articulated plate. Telson broad, with two pairs of small cuspidate setae on dorsal surface; posterior margin rounded, with two pairs of stout spiniform setae, mesial very long; anal tubercles absent. Eyes fully concealed in dorsal view, partly exposed in lateral view. Antennular peduncle stout, with sharp tooth on mesioventral carina of first article; stylocerite short, appressed, with blunt tip not reaching distal margin of first article; lateral flagellum with well-developed accessory ramus. Antenna with very stout basicerite armed with large triangular tooth; scaphocerite short, not reaching end of antennular peduncle, with blade somewhat reduced and not reaching small distolateral tooth; carpocerite robust, overreaching both scaphocerite and antennular peduncle. Mouthparts not particularly modified, typical for family; mandible with palp subtly subdivided into two articles; maxillule, maxilla, first and second maxillipeds without particular features. Third maxilliped narrow, pediform; coxa with broadly square-shaped lateral plate; ultimate article slightly tapering, tip armed with two robust spiniform setae. Chelipeds modestly enlarged, equal in size and symmetrical in shape, carried extended; basis and ischium short, robust; merus very robust, flattened ventrally, unarmed; carpus short, cup-shaped, mesial surface without setal rows; chela slightly enlarged, smooth, without grooves, subcylindrical; fingers without snapping mechanism, cutting edge of each finger armed with one simple large stout tooth. Second pereiopod with ischium unarmed; merus distinctly shorter than ischium; carpus with five subarticles, first longest; chela simple. Third, fourth and fifth pereiopods robust; ischia with one cuspidate seta; meri with two, three and four very thick cuspidate setae, respectively; carpi with small distoventral spiniform seta; propodi of third and fourth pereiopod with one or two slender spiniform setae, propodus of fifth pereiopod with well-developed setal brush; dactyli simple, conical. Second pleopod with appendix masculina in males only. Uropod with broadly rounded lateral lobe of protopod; exopod without distolateral tooth, two thick distolateral spiniform setae originating from swollen, somewhat elevated lateral portion of diaeresis; distal and distomesial margins of exopod and endopod with row of slender spiniform setae. Gill/exopod formula: 5 pleurobranchs (above P1–5); 1 arthrobranch (at Mxp3); 0 podobranchs; 2 lobe-shaped epipods (Mxp1–2); 5 mastigobranchs (Mxp3, P1–4), 5 sets of setobranchs (P1–5); 3 exopods (Mxp1–3).

Type species. Pachelpheus pachyacanthus sp. nov., by present designation.

Other species included. None.

Distribution. Eastern Pacific: currently only known from the Coiba Archipelago, Panama.

Etymology. The new genus is named after the author’s friend and Brazilian caridean shrimp expert, Paulo P.G. Pachelle, who participated in the collection of the below described type species. The name is a combination of the first six letters of Paulo’s second (citation) name and the last five letters of Alpheus Fabricius, 1798 , the type genus of the family Alpheidae . Gender masculine.

Remarks. Pachelpheus gen. nov. can be characterised and separated from all other alpheid genera by the combination of the following characters: (1) frontal margin of carapace with broadly rounded rostral projection, i.e. without a well-delimited rostrum and also without orbital teeth; (2) sixth pleonite with a triangular articulated plate (= flap) at the posteroventral angle; (3) telson with two pairs of cuspidate setae dorsally, without anal tubercles ventrally; (4) eyes concealed in dorsal view, partly visible in lateral view; (5) chelipeds equal in size, symmetrical in shape, moderately enlarged, stout, carried extended; (6) cheliped carpus without rows of setae mesially; (7) cheliped fingers without snapping mechanism, each finger armed with one stout tooth; (8) second pereiopod carpus with five subarticles; (9) third, fourth and fifth pereiopods with ischia armed with single robust cuspidate seta, meri armed with two to four unusually robust cuspidate setae; (10) second pleopod with appendix masculina in males only; (11) uropodal exopod and endopod with rows of slender spiniform setae on their distal and distomesial margins; (12) uropodal diaeresis unusually thickened laterally, with two very stout spiniform setae; and (13) lateral lobe of uropodal protopod broadly rounded, without distal tooth. The characters (9), (11) and (12) are autapomorphies for Pachelpheus gen. nov. for they do not occur, at least not in this form, in any other currently known alpheid genus.

The phylogenetic position of Pachelpheus gen. nov. is presently unknown. In the eastern Pacific, the new genus appears to be at least superficially similar to Leslibetaeus , sharing with the latter genus characters (1), (3), (4), (5), (7), (8) and (10), but differing from it by characters (2), (6), (9), (11), (12) and (13). Pachelpheus gen. nov. and Leslibetaeus are superficially similar in the general configuration of the frontal margin of the carapace and cephalic appendages, i.e. antennules and antennae (especially the shape and length of the scaphocerite), and also in the general shape of the chelipeds. However, in both species of Leslibetaeus , the sixth pleonite has no trace of an articulated plate at the posteroventral angle; the cheliped carpus has short transverse rows of setae on the mesial surface; the third to fifth pereiopod ischia amd meri are unarmed; the uropodal exopod and endopod are devoid of rows of slender spiniform setae on their margins, whilst the exopod has a typical, single distolateral spiniform seta ( Anker et al. 2006b; Anker 2011c). In addition, at least in the type species of Leslibetaeus , the second carpal subarticle of the second pereiopod is longer than the first ( Anker et al. 2006b), as opposed to the first being much longer than the second in the new genus. All these differences suggest that Pachelpheus gen. nov. and Leslibetaeus are only distantly related, if at all.

Alpheopsis Coutière, 1897 is represented in the eastern Pacific by at least three species ( Wicksten 1983; Wicksten & Hendrickx 2003; A. Anker, pers. obs.) and shares more than half of the above characteristics with Pachelpheus gen. nov., e.g., (2), (3), (4), (5), (6), (7), (8) and (10), although most of them are plesiomorphies within the family. Most notably, the two genera share the presence of an articulated flap at the posteroventral angle of the sixth pleonite. On the other hand, the general configuration of the frontal region of Pachelpheus gen. nov. is rather different from that of Alpheopsis , approaching much more that of Leslibetaeus (see above). All other eastern Pacific alpheid genera ( Wicksten & Hendrickx 2003) seem to be much more distantly related to Pachelpheus gen. nov., based on their morphological characteristics. The same can be stated for all Atlantic genera, since none of them morphologically approaches the herein described new genus.

On the other hand, Pachelpheus gen. nov. has several morphological similarities with the western Pacific Jengalpheops Anker & Dworschak, 2007 , currently containing only the type species, J. rufus Anker & Dworschak, 2007 , from the Philippines and Indonesia ( Anker & Dworschak 2007; Anker et al. 2015). These two genera are similar in the general configuration of the frontal region [character (1), see above], the presence of an articulated plate on the sixth pleonite [character (2)], the development (size), shape and armature of the chelipeds [characters (5), (7)], the blunt lateral lobe of the uropodal protopod [character (13)], and some other, mostly plesiomorphic features [e.g., characters (8) and (10)]. The chela of some larger individuals of J. rufus resembles that of the type species of Pachelpheus gen. nov. not only in size and form, but also in the arrangement of the teeth on the cutting edges, i.e. one large proximal tooth on the dactylus and one more distal tooth on the pollex, with the corresponding hiatuses (cf. Fig. 4 below and Anker & Dworschak 2007: fig. 4I). Pachelpheus gen. nov. and Jengalpheops can be easily separated from each other by characters (9), (11) and (12), which are autapomorphies of the new genus, as well as by characters (4) and (6). With regard to character (9), it is important to note that the meri of the third to fifth pereiopods of Jengalpheops are also armed with cuspidate setae and that the main difference between the two genera lies in their size, shape and number: in Jengalpheops , they are small, conical and not numerous (one or two), whilst in the new genus, they are highly modified, very large, robust, flattened, and more numerous (three to five) (see below). The absence of setal rows in the mesial face of the cheliped carpus in Pachelpheus gen. nov. [character (6)] versus their presence in Jengalpheops (and also in Leslibetaeus ) is another important differentiating character, although this feature is known to be variable at least in Potamalpheops Powell, 1979 . Another difference between Pachelpheus gen. nov. and Jengalpheops lies in the shape of the lateral plate on the third maxilliped coxa, almost square-shaped in the former and styliform in the latter (cf. Fig. 3G below and Anker & Dworschak 2007: fig. 3I). Whether Pachelpheus gen. nov. and Jengalpheops are also closely related phylogenetically, remains to be shown by a thorough phylogenetic analysis of the family (morphology + DNA) at the generic level.

The only genera characterised by the absence of a well-developed rostrum, the presence of an articulated flap on the sixth pleonite, and the chelipeds subequal and subsymmetrical, carried extended (not folded), are Betaeus Dana, 1852 and Betaeopsis Yaldwyn, 1971 . However, both of these genera are very different from Pachelpheus gen. nov. in a number of other characters ( Banner & Banner 1973; Anker & Jeng 2002; Anker & Baeza 2012).

Figures

FIGURE 3. Pachelpheus pachyacanthus gen. et sp. nov., paratype, female (cl 3.6 mm) from Isla Rancheria, Coiba Archipelago, Panama (FLMNH UF 51918): A—mandible, mesial view; B—maxillule, lateral view; C—maxilla, lateral view; D—first maxilliped, lateral view; E—same, endopod, mesial view; F—second maxilliped, lateral view; G—third maxilliped, lateral view; H—same, apex of ultimate article, lateral view.

FIGURE 4. Pachelpheus pachyacanthus gen. et sp. nov., holotype, male (cl 3.5 mm) from Isla Rancheria, Coiba Archipelago, Panama (FLMNH UF 51917):A—right cheliped, lateral view; B—same, distal portion of merus, carpus and chela, mesial view; C—same, merus and carpus, mesial view; D—same, carpus and chela, lateral view.