Potamalpheops johnsoni, Anker, 2003

Anker, Arthur, 2003, Alpheid Shrimps From The Mangroves And Mudflats Of Singapore. Part I. Genera Salmoneus, Athanas And Potamalpheops, With The Description Of Two New Species (Crustacea: Decapoda: Caridea), Raffles Bulletin of Zoology 51 (2), pp. 283-314 : 290-294

Potamalpheops johnsoni , new species

( Figs. 5-7, 20c, d)

Potamalpheops tigger Yeo & Ng, 1997: 182 (part, 1 specimen from ZRC type-series).

Material examined. – Holotype – 1 ovig. female (CL 3.7 mm), ZRC 2000.2172 , Sungei Buloh mangrove forest, Singapore, coll. Y. Cai, 29 Jan.2000.

Paratypes – 1 ovig. female (CL 4.2 mm), ZRC 2000.2173 , 2 females (CL 3.7 mm and 2.8 mm), ZRC 2000.2178 - 79 , 1 ovig. female (CL 3.4 mm), USNM 1005101 , 1 female (CL 3.9 mm), RMNH D 50011 , 1 ovig. female (CL 3.7 mm) and 1 post-ovig. female (CL 4.6 mm), MNHN-Na 13755, all same data as for holotype ; 1 female (CL 4.4 mm), ZRC 1999.0035 , Sungei Buloh mangrove , Singapore, coll. P.K.L. Ng and D. C. J. Yeo, 01 Mar.1998; 1 male (CL 3.1 mm), ZRC 2000.2171 , Sungei Buloh mangrove , Singapore, coll. PL E, 10 Oct.1992; 1 female (CL 2.6 mm), ZRC 2003.0088 (from paratype series of P. tigger, ZRC 1996.7) , Sungei Buloh mangrove, Singapore, 05 Aug.1995, coll. P.K.L. Ng; 1 ovig. female (CL 3.9 mm), 1 male (CL 2.7 mm) and 1 immature specimen (CL not measured), ZRC 2000.2182 - 84 , Sungei Buloh mangrove , Singapore, from mud, under pieces of rotten wood and from water holes at low tide, coll. A. Anker & Y. Cai, 10 Feb.2000; 1 male (CL 2.9 mm) and 1 female, dissected (CL 4.4 mm), MNHN-Na 13720, same data as for ZRC 2000.2182-84.

Description. – Carapace smooth, glabrous, not setose. Rostrum usually exceeding distal margin of first article of antennular peduncle ( Figs. 5a,b), laterally compressed, acute, with small subdistal acute tooth on inferior margin ( Figs. 5 b-j), sometimes with two very small teeth ( Figs. 5e, f). Extra-corneal teeth well developed, acute, infra-corneal angle slightly produced anteriorly, rounded. Eyes partially exposed in dorsal and lateral views, cornea large, well pigmented, medio-anterior margin lacking tubercle or long setae. Pterygostomial angle slightly projecting anteriorly, rounded ( Fig. 5b), without plumose setae.

Antennular peduncles not elongated, second article slightly longer than first; stylocerite acute, exceeding distal margin of first article ( Figs. 5a, 6q); mesio-ventral carina with well developed, acute tooth ( Fig. 6q); outer flagellum biramous, with the shorter ramus partly fused to the main ramus ( Fig. 6r), aesthetasc tufts scarce, more developed and numerous towards the distal end of the short ramus in females ( Fig. 6q), generally more developed and more numerous, extending from the third or fourth joint to the distal end of the short ramus in males ( Fig. 6r). Antenna with basicerite bearing acute ventro-lateral tooth; scaphocerite reaching but not exceeding distal margin of antennular peduncles, lateral spine strong, anterior margin convex ( Fig. 6o), carpocerite very short, reaching to about 3/5 of scaphocerite.

Mouthparts typical for Potamalpheops . Mandible with twoarticulated palp; incisor process with six short, triangular teeth. Maxillule, maxilla, first and second maxillipeds as illustrated ( Figs. 7 c-e), without specific features. Third maxilliped ( Fig. 7f) slender; coxa with epipod and lateral plate well developed, latter with some setae ( Fig. 7g); tip of ultimate segment with one subdistal spine and one distal spine ( Fig. 7h); arthrobranch well developed ( Figs. 7f, g).

First chelipeds ( Figs. 6 a-d) symmetrical, not enlarged; not sexually dimorphic; coxa with strap-like epipod and at least four setobranchial setae; ischium stout; merus much longer than ischium and distinctly longer than carpus; carpus cylindrical, with several (usually six to seven) rows of grooming setae mesially ( Figs. 6b, d); chela slightly longer than carpus, fingers clearly shorter than palm ( Fig. 6c), distally with numerous tufts of setae; cutting edges unarmed.

Second pereiopod slender, coxa with strap-like epipod and at least four to five setobranchial setae; ischium and merus subqual, slender; carpus five-articulated, ratio of carpal articles equal approximately to (proximal to distal): 4-1-1.2- 1-2 ( Fig. 6e); chela simple, longer than distal carpal article but much shorter than first carpal article.

Third pereiopod ( Fig. 6f) rather slender; coxa with strap-like epipod and four to five setobranchs; ischium armed with one spine, merus armed with 2 spines; carpus unarmed; propodus armed with two or three slender spines on inferior margin and a distal pair of spines ( Fig. 6g); dactylus about 0.4 length of propodus, simple, slender, slightly curved ( Fig. 6g). Fourth pereiopod very similar to third pereiopod, but with propodus armed with four to five smaller spines ( Fig.6 h). Fifth pereiopod with coxa bearing only setobranch, ischium and merus unarmed (at least in female); propodus with several small spines and a well developed brush of grooming setae ( Fig. 6i).

Abdominal segments with posterior ventral angles rounded, sixth segment with articulated triangular plate. Uropod with diaeresis finely toothed (around 25 very small teeth in one of the paratypes) on about 2/3 of its length, then abruptly curved and ending ( Fig. 6n); lateral spine well developed. Telson elongate, slightly tapering distally, with two pairs of dorsal spines in most specimens ( Fig. 6l), exceptionally with three pairs ( Fig. 6j); posterior margin of telson medially convex, with two, rarely three strong postero-lateral spines at each angle ( Figs. 6l, k), median spines somewhat longer than lateral spines.

Gill formula typical for genus ( Powell, 1979): pleurobranchs on P1-P5; podobranch absent; arthrobranch on Mxp3; exopods on Mxp1-Mxp3; strap-like epipods (mastigobranchs) on Mxp3 and P1-P4; setobranchs on P1- P5.

Largest specimens reaching approximately 4.5 mm CL (12 mm TL).

Colour. – Grey, semi-translucent, large blackish or brownish chromatophores forming broad bands on each abdominal segment and most of the carapace ( Figs. 20c, d); first chelipeds, especially chela, and third to fifth pereiopods flecked with small chromatophores. In some individuals the pattern is less distinct, sometimes the banding is diffuse and hardly distinct.

Habitat. – Potamalpheops johnsoni , new species, has been collected by hand either washing out the soft mud close to small mangrove pools or under pieces of dead rotten wood. Potamalpheops tigger and P. johnsoni , new species, may have finely tuned differences in their ecological niches, involving parameters such as intertidal zonation and seasonality, or reproductive patterns. For instance, the eggs in ovigerous females are slightly larger in P. johnsoni new species, than in P. tigger . Also, P. johnsoni , new species, could be either the rarer of the two species or more abundant during a certain season only.

Remarks. – Potamalpheops johnsoni , new species, belongs to the P. monodi species group, characterized by two spines at each posterior angle of the telson (Yeo & Ng, l997), and by the presence of a well developed row of setae on the mesial side of the carpus of the first pereipods ( Fig. 6d). Within the P. monodi group, it can be contrasted to species characterized by a well developed, elongate rostrum, and not especially enlarged chelae of the first pereiopods. These are P. pininsulue Bruce & Iliffe from the anchialine caves of New Caledonia (Bruce & Iliffe, 1992) and P. tigger Yeo & Ng , which occurs in Singapore syntopically with P. johnsoni , new species, and is also known from northern Australia (see earlier). Potamalpheops johnsoni , new species, can be separated from the slightly larger P. pininsulae by the dorsally much less convex carapace (cf. Bruce & Iliffe, 1992: fig.1), the rostrum with the inferior tooth (or teeth) situated more apically (cf. Bruce & Iliffe, 1992: figs. 2, 4), the second and third pereiopods less slender (cf. Bruce & Iliffe, 1992: fig. 23), and the appendix masculina lacking a row of setae on the margin opposed to the endopod, as illustrated by Bruce & Iliffe (1992: fig. 31).

Potamalpheops johnsoni , new species, differs from P. tigger by the rostrum bearing a subapical inferior tooth, which is never present or even indicated in P. tigger (cf. Fig. 4) and the much shorter stylocerite (cf. Figs. 5b, 4c). The colour patterns also contribute to the separation of these two syntopic species: probably the most consistent difference (though visible only under the dissecting microscope) is the presence of blackish or brownish chromatophores on the third to fifth pereiopods in P. johnsoni , new species, and their absence in P. tigger .

All other Potamalpheops species with non enlarged or “primitive” chelipeds, namely P. amnicus Yeo & Ng , P. miyai Yeo & Ng , P. monodi Sollaud , P. stygicola Hobbs , P. hanleyi Bruce , an undescribed species of Potamalpehops from Palawan (Cai & Anker, in prep.) and a second undescribed species from Nigeria (cf. Powell, 1979, addendum, p. 150), have much shorter rostrums and differ from P. johnsoni , new species, in numerous other features (cf. Gordon, 1957; Powell, 1979; Hobbs, 1973, 1983; Bruce, 1991; Yeo & Ng, 1997).

Distribution. – Presently known only from the type locality, Sungei Buloh mangrove in Singapore.