Potamalpheops tigger Yeo & Ng, 1997

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 : 288-290

Potamalpheops tigger Yeo & Ng, 1997

( Figs. 4 , 20a, b , 21)

Potamalpheops tigger Yeo & Ng, 1997: 182 , figs. 5, 6.

Material examined. – Type series of P. tigger, ZRC 1996.6-7 (for details see Yeo & Ng, 1997); 1 specimen (sex and CL not noted), ZRC 2000.2158 , Sungei Buloh mangrove, Singapore, coll. P3 E, 21 Sep.1992 ; 2 specimens (sex and CL not noted), ZRC 2000.2159 - 2160 , Sungei Buloh mangrove, Singapore, coll. Y. X. Cai, 29 Jan.2000 ; 8 specimens (sex and CL not noted), ZRC 2000.2161 - 2168 , Sungei Buloh mangrove, Singapore, in mud under debris and dead wood, coll. A. Anker & Y. Cai, 10. Feb.2000 .

Extra-limital material. – 1 female (CL 3.1 mm), NTM Cr-013092, near bridge, Channel Darwin Island , Northern Territory, Australia, 12 3 9’ S, 130 55.4’ E, LWS, Site 3, coll. M. Burke, 14 Jul.1991 .

Diagnosis. – Carapace glabrous, without grooves; rostrum straight ( Figs. 4b, f, h ) sometimes slightly descendant towards the tip ( Figs. 4a, d ), acute, very narrow in some specimens ( Fig. 4a ), reaching at least to distal third of first article of antennular peduncle, and at most to mid-length of second article (cf. Figs. 4 a-c, k), without any trace of a tooth on inferior margin; extra-corneal teeth triangular, acute; eyes exposed in dorsal and lateral views, concealed only proximally, corneas well developed, setae on medio-anterior margin absent; infra-corneal region protruding and rounded; pterygostomial region rounded, without plumose setae; second article of antennular peduncle approximately as long as visible portion of first article; stylocerite acute, reaching far beyond second article of antennular peduncle in most specimens ( Fig. 4a ), but only to posterior third of second article in some specimens ( Fig. 4c ); antennular flagellum biramous, fused portion containing usually more than six joints, males with usually more than 15 tufts of aesthetascs, females with few (five to six or even less) aesthetasc groups; lateral spine of scaphocerite exceeding anterior margin, latter slightly convex; tip of third maxilliped with small spines; first chelipeds symmetrical, not sexually dimorphic, not particularly enlarged, held extended or simply folded beneath cephalothorax, carpus cylindrical, with rows of setae on mesial face ( Fig. 4i ), chela simple, with cutting edges unarmed; carpus of second pereiopod five-articulated, first article longest, slightly longer than fifth; third, fourth and fifth pereiopods with ischium armed with one spine; merus of same appendages armed with two spines; propodus armed with small spines, dactylus slender, slightly curved; appendix masculina with four spines (at least in specimens examined); uropod with diaeresis bearing 17-24 teeth; telson rectangular, narrow, tapering posteriorly, with two pairs of dorsal spines, first pair situated usually just anterior to telson mid-length; posterior margin of telson medially rounded, with two spines, median spines longer than lateral spines; gill formula as given for genus ( Powell, 1979; see also description of new species below).

Colour. – Grey, semi-translucent, with blackish chromatophores forming broad bands on each abdominal segment and carapace ( Figs. 20a, b ); observed dorsally, some parasagittal or sagittal-oblique areas are lacking chromatophores. Shrimps are apparently able to adapt their colour pattern to the background or to light conditions; this may explain why some specimens appear rather spotted, and not banded, while others present reddish-brown instead of blackish banding (Fig. 21).

Remarks. – Potamalpheops tigger was described in detail and illustrated by Yeo & Ng (1997), who noted, but did not figure a large intra-specific variation, especially in the length of the rostrum and the stylocerite. One character on the first chelipeds important for the taxonomy and phylogeny of the genus was not mentioned in the original description. The mesial face of the carpus bears several comb-like rows of setae in P. tigger , but also in P. miyai Yeo & Ng , P. amnicus Yeo & Ng and all other species of the P. monodi group, and also in P. stygicola (Hobbs) (pers. obs.). The number of the asthetascs on the antennules appears to be sexually dimorphic in P. tigger and possibly in other species of Potamalpheops (pers. obs.). This specimen represents a considerable range extension of P. tigger from Southeast Asia to northern Australia. In light of this new data, the short updated diagnosis of P. tigger provided above completes the fuller original description given by Yeo & Ng (1997).

Although the variation in the shape of the rostrum is rather large, it is still considered here as intra-specific. Interestingly, a similar type of rostral variation is observed in two other species of the genus Potamalpheops also characterized by the presence of a long rostrum. One of them is the new species described below (cf. Fig. 5 ); the other is P. pininsulae (cf. Bruce & Iliffe, 1992: figs. 48-53). In these two species, the variation affects not only the rostral length and shape (e.g., narrow vs. broad laterally, straight vs. slightly descendant), but also the degree of development of the inferior subapical tooth. The specimen from Channel Island near Darwin, Northern Territory (NTM Cr-013092) has the longest and most slender rostrum among the specimens examined ( Fig. 4k ); this specimen has furthermore the carpus of the first pereiopods slightly shorter than in the Singapore specimens (cf. Fig. 4l ). In all other characters this female agrees well with P. tigger .

The length of the stylocerite is more or less constant in other species of Potamalpheops . In P. tigger there is apparently no correlation between the length of the stylocerite and other important features, e.g., rostrum length, or sex and age of specimens. Therefore, this feature is seen here as undergoing intra-specific variation. However, it would be most interesting to analyze the genetic structure of Potamalpheops populations in the Sungei Buloh mangrove, to verify the eventual presence of cryptic species.

Distribution. – Until now, Potamalpheops tigger was known only from Sungei Buloh and Lim Chu Kang mangrove swamp forests in Singapore. The female specimen collected on Channel Island near Darwin, Northern Territory, is the first record of this species outside Singapore and represents a range extension of this species from South-East Asia to northern Australia.

Figures

Fig. 4. Potamalpheops tigger Yeo & Ng, a-j, series of specimens from Sungei Buloh (ZRC and MNHN): a-c, frontal region of males (a, b) and ovigerous female (c); d-h, variation of rostrum in males (d-f, h) and post-ovigerous female (g); i, first cheliped, carpus and chela, inner view; j, second pleopod, appendix masculina and appendix interna; k-m, female from Darwin (NTM Cr-013092): k, frontal region, lateral view; l, first pereiopod; m, second pereiopod. Scale: 1 mm.

Fig. 20. Colour patterns of some Alpheidae from Sungei Buloh, Singapore: a, b, Potamalpheops tigger Yeo & Ng; c, d, Potamalpheops johnsoni, new species; e, f, Athanas polymorphus Kemp. All more or less to scale.

Fig. 5. Potamalpheops johnsoni, new species, a, b, paratype, ovigerous female (MNHN-Na 13720), frontal region in dorsal (a) and lateral (b) views; c, holotype, ovigerous female (ZRC 2000.2172), rostrum; d-j, paratype series, males (g-i), female (j), ovigerous females (df), variation of rostrum. Scale: 1 mm.