Salmoneus singaporensis, 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 : 284-288

Salmoneus singaporensis , new species

( Figs. 1 , 2, 3a, b )

Salmoneus hilarulus – Johnson, 1962: 49 (part.)(not De Man, 1910).

Material examined. – Holotype - non ovigerous specimen, probably male (CL 8.9 mm), ZRC 1979-4615 , with label “ Salmoneus hilarulus De Man ”, Tanjong Penuru , Jurong, Singapore, mudflats, coll. Honours, University of Malaya, 24 Jul.1959, id. D. Johnson.

Comparative material. – Salmoneus rostratus Barnard, 1962 , 1 ovigerous female (CL 6.3 mm), MNHN-Na 13671, Ao Tang Khen, Phuket, Thailand, intertidal, sand-flats, from burrow of Alpheus cf. rapacida , coll. T. Komai, 24 Oct.1995; 1 non-ovigerous specimen, probably male (CL 6.4 mm), MNHN-Na 4787, Nosy-Bé, Madagascar, intertidal, coll. B. Opic, 07 Sep.1974 id., Banner & Banner (specimen reported in Banner & Banner, 1983).

Description. – Carapace very sparsely setose, with a small, flattened tubercle posterior to rostrum ( Fig. 3a ). Rostrum very long and slender, reaching almost to midlength of second article of antennular peduncle; inferior margin of rostrum with small, acute, subdistal tooth ( Fig. 2c); base of rostrum approximately equal to one third of rostrum length in dorsal view. Extra-corneal teeth well developed, acute. Eyestalks partially visible in dorsal and lateral views, each bearing a small anterior tubercle; corneas somewhat reduced ( Figs. 2c, 3a ). Pterygostomial angle broadly rounded.

Antennular peduncle robust, second article slightly longer than visible portion of first article, stylocerite acute, slightly exceeding distal margin of first antennular article; mesio-ventral carina with acute tooth; outer flagellum biramous, shorter ramus quite long, well separated from main ramus ( Fig. 2c), basal fused portion with four joints. Antenna with basicerite robust, bearing acute ventro-lateral tooth; carpocerite very robust, somewhat elongated, not reaching distal margin of third antennular article; flagellum very robust; scaphocerite blade with anterior margin slightly convex; lateral spine strong, exceeding anterior margin of scaphocerite, but not reaching distal margin of antennular peduncle. Mouthparts not dissected to avoid damage of the unique holotype specimen (usually not species-specific within Salmoneus , pers. obs.).

First chelipeds very asymmetrical in shape and unequal in size, both held flexed ventrally. Major cheliped with ischium and merus very slender ( Fig. 2e); chela twisted, palm with a deep groove extending from its proximal margin to propodo-dactylar articulation; both fingers, especially dactylus, strongly curved distally ( Fig. 2f); both dactylus and pollex armed with rounded or triangular teeth, two most proximal teeth largest and triangular, distal teeth rather small and rounded; distal third of pollex and distal fifth of dactylus without teeth ( Fig. 3b ). Minor cheliped much shorter than major cheliped, with chela simple and unarmed, carpus, elongated, approximately 6 times as long as wide ( Fig. 2a).

Second pereiopod slender, carpus five-articulated, with first article longer than all other articles combined, ratio of carpal articles approximately equal to 6.0: 0.9: 0.8: 0.8: 1.5 ( Fig. 2a). Third to fifth pereiopods (P3-5) slender, ischium armed with two spines on P3 and P4, unarmed on P5; merus longer than carpus, latter subequal to (P3) or shorter than (P5) propodus; propodus unarmed except small distal spinules on P3 and P4 ( Fig. 2g); P5 distally with rows of setae; dactylus simple, elongated, very slender, slightly curved ( Figs. 2a, g), 0.35-0.4 length of propodus.

Abdominal segments (A) with postero-ventral angles rounded (A2, A3), angular (A4) or produced in a acute tooth (A5, A6), posterior margin of A6 acutely produced laterodorsally ( Fig. 1 ); preanal plate acutely produced. Telson rectangular, distally tapering, with two pairs of dorsal spines anterior pair situated approximately on mid-length; posterior margin truncated with a small median incision ( Fig. 2d), lateral posterior spines by 1/3 shorter than median spines.

Gill formula typical for Salmoneus : 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.

Colour. – Colour in life not noted.

Habitat. – The unique holotype of S. singaporensis , new species, was collected at low tide on a mudflat.

Remarks. – The genus Salmoneus Holthuis, 1955 , contains 19 valid and several undescribed species (pers. obs.) that can be divided roughly into two species groups. The first, more homogenous species group includes only four species, all found in the temperate and tropical waters of the eastern Atlantic Ocean from the Mediterranean Sea south to Nigeria. These four species are characterized by the minor cheliped being as long or even longer (although less robust) than the major cheliped (cf. Holthuis, 1951; Fransen, 1992; Dworschak et al., 2000). All other species of Salmoneus are characterized by the minor cheliped being much smaller than the major cheliped (with the exception of an undescribed species from northern Australia, pers, obs.). They form a vast heterogenous group, widely distributed in the central and western Atlantic (five species), the eastern Atlantic (one undescribed species in the eastern Mediterranean, G. Grippa, pers. comm.), the eastern tropical Pacific (two species) and the Indo-West Pacific (12 species). Several species, e.g., S. cavicolus Felder & Manning , and the type-species, S. serratidigitus Coutière (sensu Banner & Banner, 1981) are extremely variable in the shape of the frontal region. Those species could represent several species, and are in need of a thorough revision.

Salmoneus singaporensis , new species, appears to be closest to S. rostratus Barnard , a geographically widespread but rarely collected species. Salmoneus rostratus is up to present known only from three localities: Nosy-Bé, Madagascar ( Barnard, 1962; Banner & Banner, 1983), Hansa Bay, Papua New Guinea (De Grave & Wilkins, 1997) and Phuket, Thailand (present study, new record). The unique specimen of S. singaporensis , new species, differs from all specimens of S. rostratus personally examined (see comparative material) or illustrated in the literature ( Barnard, 1962; De Grave & Wilkins, 1997), by the following features: (1) inconspicuous post-rostral tubercle (cf. Figs. 3a, d ); (2) rostrum being less slender and more elongated (cf. Figs. 3a, d ); and (3) presence of rounded teeth on the distal half of major chela fingers, especially on the dactylus (cf. Figs. 3b, c ). The armature of the major chela is considered to be an important character in the taxonomy of Salmoneus species. In view of the quasi-non extant variability in the chela armature among three specimens of S. rostratus from geographically very distant localities (see above), the different armature in S. singaporensis , new species, along with the feebly developed post-rostral tubercle, justify the erection of a new species. Furthermore S. singaporensis , new species, also has a series of shallow, rounded depressions above each tooth of the dactylar cutting edge on the major chela ( Fig. 3b ); these depressions are not distinct on the chela of Phuket specimens ( Fig. 3c ).

It is unlikely that the above listed differences between S. singaporensis , new species, and S. rostratus are examples of intra-specific variation of the latter species, however, more specimens of both species from Singapore and elsewhere are needed to confirm the validity of the new species. Because of the shape of the major chela, the large rounded teeth on the cutting edges of the major cheliped, the presence of a post-rostral tubercle (much less developed in S. singaporensis , new species), the very robust antennal flagellum and carpocerite, the small tubercle on the anterior margin of each eyestalk, and the elongated narrow rostrum armed with a second inferior tooth, S. singaporensis , new species, and S. rostratus occupy a rather isolated position within Salmoneus .

Two other species of Salmoneus appear relatively distantly related to the new species and to S. rostratus . Salmoneus bruni Banner & Banner could be the next closest relative of these two species, at least in the shape of the major chela. However, S. bruni can be distinguished from S. singaporensis new species, by the much shorter rostrum lacking an inferior subdistal tooth and, by the central portion of the cutting edges of the major chela lacking teeth (cf. Banner & Banner, 1966b), as in S. rostratus . The description of Salmoneus tafaongae was based on a «fragmentary» ovigerous female collected on «outer portion of fringing reef, shoreward of surf zone, about 1 foot below low water, 3 miles east of Apia, Upolu, Western Samoa » ( Banner & Banner, 1966a). This specimen was lacking the major cheliped. No figures were provided, instead Banner & Banner stated that «it was unfortunate that this single specimen was not more nearly intact, and that the small chela and second legs were lost after the initial examination. However, because its form is so distinctive we have decided to describe it as a new species». It was a very unfortunate decision; even if the holotype still exists, which seems unlikely (it is neither in the USNM – pers. obs., nor in the BPBM – L. Eldregde, pers. com.), it would not be very helpful for comparisons with other species.

Several features from the original text description suggest that S. tafaongae could be indeed closely related to S. singaporensis , new species, especially in having (1) elongated rostrum (three times as long as broad in S. tafaongae ), with an acute tip and bearing a small tooth; (2) eyes partly exposed dorsally between the extra-corneal teeth and the rostrum, with most of the corneal surface also visible laterally; (3) third to fifth pereiopods elongate and slender, with dactylus simple, slightly curved, seven times as long as broad; and (4) telson with posterior margin bearing a small «trapeziform» median incision. However, S. singaporensis , new species, differs from S. tafaongae in having shorter stylocerite, which slightly exceeds the first antennular article (in S. tafaongae the stylocerite reaches to the end of the second antennular article), the squamous portion of the scaphocerite not exceeding its lateral spine as in S. tafaongae , and longer and stouter carpocerite of the antenna, which reaches to the third antennular article in S. singaporensis , new species, while it does not reach to the middle of the second article in S. tafaongae . Finally, the habitats where the two specimens were collected are quite different: S. singaporensis , new species, was collected on mudflats, while S. tafaongae was collected on the outer fringing reef.

The type-locality of S. singaporensis , new species, Tanjong Penuru, was a mudflat locality on the southern shore of Jurong, Singapore. Unfortunately, it is no longer extant so no further topotypic specimens could be collected in Singapore. The new species is characterized by extremely slender, slightly curved dactyli of third to fifth pereiopods, typical for species adapted for walking on soft bottoms, such as S. ortmanni Rankin , a pan-American species found in mangroves, and S. rostratus which seems to occur in similar, sandy-muddy habitats ( Barnard, 1962; De Grave & Wilkins, 1997). Significantly, the present specimens of S. rostratus from Phuket were collected from a burrow of the quite large, goby-associated snapping shrimp Alpheus cf. rapacida (T. Komai, pers. comm.). Previously, De Grave & Wilkins (1997) reported a possible association of S. rostratus with the goby Mahidolia mystacina (Valenciennes) . Yanagisawa (1978) also reported M. mystacina as an associate of Alpheus sp. in Japan, and colour slides by R. Kuiter show several species of Alpheus (all from brevirostris group) sharing its burrow with M. mystacina in Indonesia. Thus S. rostratus may actually be associated with burrows excavated by larger Alpheus species and shared with gobies, such as M. mystacina .

Distribution. – Known only from the type-locality in Singapore, which is no longer extant (see above).

Figures

Fig. 1. Salmoneus singaporensis, new species, holotype, probably male, habitus. Scale: 1 mm.

Fig. 3. Salmoneus singaporensis, new species, holotype, probably male (a, b) and Salmoneus rostratus Barnard, ovigerous female from Phuket, Thailand (c, d): a, c, frontal region, lateral view; b, d, major chela, distal portion of palm and fingers. Scales: A (a, b), B (c, d), both scales 1 mm.