Salmoneus falcidactylus, Marin, 2006

Marin, Arthur Anker Ivan N., 2006, New Records And Species Of Alpheidae (Crustacea: Decapoda) From Vietnam. Part I. Genus Salmoneus Holthuis, 1955, Raffles Bulletin of Zoology 54 (2), pp. 295-319 : 304-307

publication ID	https://doi.org/ 10.5281/zenodo.13245424
persistent identifier	https://treatment.plazi.org/id/03AB572D-FFED-FFBA-FF65-FED0FE15DB46
treatment provided by	Felipe
scientific name	Salmoneus falcidactylus
status	sp. nov.

Treatment

Salmoneus falcidactylus View in CoL , new species

( Figs. 8 View Fig , 9 View Fig )

Material examined. – Holotype, non ovigerous specimen (CL 1.9, TL 5.9)( ZMMU Ma 5439), South China Sea ; Vietnam, Nhatrang Bay , station Nr 6, about 2 km SW off Mung Island, on muddy bottom, depth 40 m, coll. O. Savinkin, I. Marin & A. Beliaev, 17 Oct.2003.

Description. – Carapace non-setose, glabrous ( Figs. 8 View Fig , 9c View Fig ), laterally with shallow oblique depressions. Rostrum elongate, reaching distal 3/4 of second segment of antennular peduncle ( Fig. 9a View Fig ), longer than broad at base; lateral margins shallowly concave ( Fig. 9b View Fig ); rostral carina absent. Extra-corneal teeth acute, directed toward rostrum; concavity between rostrum base and extra-corneal teeth deep, U-shaped ( Fig. 9a, b View Fig ). Pterygostomial angle slightly protruding, rounded. Eyes without tubercle, only partly covered by carapace, extreme anterior portion visible in dorsal and lateral view ( Fig. 9a, c View Fig ). Epistomial sclerite with small subacute process. Ocellar beak inconspicuous.

Antennular peduncle not particularly stout; second segment shorter than first, but longer than third; ventromesial carina of first segment with acute tooth; stylocerite reaching slightly beyond mid-length of second segment, distally acute ( Fig. 9a, c View Fig ); lateral flagellum biramous, with shorter ramus situated at second segment. Antenna with basicerite bearing strong ventrolateral tooth ( Fig. 9c View Fig ); scaphocerite moderately broad, anterior margin of blade convex, not exceeding distolateral tooth; carpocerite very short, reaching to about 2/3 length of scaphocerite ( Fig. 9c View Fig ).

Mouthparts not dissected (to avoid damage of single, fragile specimen). Third maxilliped slender; ultimate segment distally tapering; arthrobranch present.

First pereiopods (chelipeds) very asymmetrical, unequal ( Fig. 9d, g View Fig ), carried flexed ventrally in life, mesially when preserved ( Fig. 8 View Fig ); major cheliped slender; ischium elongate, without spines; merus slender, elongate, distally not widening, with small rounded lobes, ventrally flattened; carpus somewhat elongate, vase-shaped, ventrally constricted, distally with two pronounced lobes ( Fig. 9e View Fig ); chela subcylindrical, with palm 3/4 length of fingers; palm proximoventrally with deep groove or constriction ( Fig. 9e View Fig ), dorsal and lateral surface with longitudinal ridges and depressions ( Fig. 9d View Fig ), ventral surface slightly flattened ( Fig. 9e View Fig ); pollex with cutting edge armed with at least 20 very small, subtriangular, regularly spaced teeth, tip acute and strongly curved; dactylus with cutting edge bearing about 20 teeth, tip acute and strongly curved ( Fig. 9f View Fig ). Minor cheliped slender; ischium elongate, equal in length to merus; carpus slightly shorter than merus, subcylindrical, distally widening; chela simple, not particularly enlarged, fingers slightly shorter than palm, cutting edges unarmed ( Fig. 9g View Fig ).

Second pereiopod slender; ischium about 5/6 length of merus; carpus with five segments having ratio of approximately 5.2/ 1/1/1/1.5; chela simple, fingers almost equal to palm ( Fig. 9h View Fig ). Third pereiopod slender; ischium with two spines; merus about 1.5 times of ischium, about 11 times as long as wide at base; carpus slender, shorter than merus, unarmed; propodus longer than carpus, ventrally unarmed except for two slender distal spines; dactylus simple, extremely slender, about 0.8 length of propodus, strongly curved, sickle-shaped ( Fig. 9i View Fig ). Fourth pereiopod similar to third. Fifth pereiopod slender; ischium unarmed; merus twice as long as ischium, about 10 times as long as wide at base; carpus slender, shorter than merus, with small distal spinule; propodus subequal to carpus, ventrally unarmed, rows of setae absent; dactylus simple, slender, about 0.8 length of propodus, strongly curved, sickle-shaped ( Fig. 9j View Fig ).

Abdominal segments I-IV with posteroventral angles rounded; segment V with posteroventral angle acutely projecting ( Fig. 8 View Fig ); segment VI with strong, acute posterior projection, without articulated plate ( Fig. 8 View Fig ); preanal plate truncate posteriorly ( Fig. 9m View Fig ). Second pleopod with appendix masculina longer than appendix interna, with two slender apical spines, almost reaching distal margin of endopod ( Fig. 9k, l View Fig ). Telson about 2.3 times as long as wide proximally; basal width about twice width of posterior margin; dorsal surface with two pairs of spines situated at some distance from lateral margin, at mid-length and about 3/4 length of telson, respectively ( Fig. 9n View Fig ); posterior margin with very shallow median notch bearing two long, fine setae and two pairs of spines, lateral much shorter than mesial ( Fig. 9o View Fig ); anal tubercles absent. Uropods slightly longer than telson; sympodite with acute tooth; diaeresis not conspicuous; lateral spine well developed, slender, reaching to distal margin of exopod ( Fig. 9 n View Fig ). Gill formula typical for genus: see under S. nhatrangensis , new species.

Colour. – Semitransparent white.

Habitat. – The specimen was collected on a muddy bottom together with a specimen of the alpheid shrimp Thuylamea camelus Xuan, 2001 , several specimens of the ogyridid shrimp Ogyrides cf. orientalis (Stimpson, 1860) , as well as some possibly juvenile unidentified mudshrimps ( Upogebiidae ).

Etymology. – The sickle-shaped form of the dactylus on the walking legs of S. falcidactylus , new species, was the origin of its name.

Remarks. – The very small size of the present specimen of S. falcidactylus , new species, would suggest that it could be juvenile. However, the presence of a well developed, elongated appendix masculina ( Fig. 9k View Fig ) leaves no doubt that the specimen is at least a subadult individual. As this specimen is also complete, and could not be assigned to any described species of Salmoneus , it is considered as a representative of a new species.

Salmoneus falcidactylus , new species, is closely related to other species characterized by the elongated rostrum; dorsally partly exposed eyes; elongated, slender dactyli on the third to fifth pereiopods; and the major chela bearing numerous small teeth on the cutting edges of both fingers, viz. S. gracilipes Miya, 1972 , S. colinorum De Grave, 2004 , S. seticheles Anker, 2003 , S. cavicolus Felder & Manning, 1986 , S. pusillus , new species (see below), and possibly S. tafaongae Banner & Banner, 1966 (chelipeds unknown). The new species can be separated from all these species by the extremely elongated, slender dactylus on the walking legs; and the much greater number of teeth (about 20) on the cutting edges of the fingers of the major chela; more specifically from S. gracilipes by the presence of two instead of three spines on the ischium of the third pereiopod, the shorter stylocerite (reaching to about mid-length of the second segment of the antennular peduncle in S. falcidactylus , new species vs. reaching to the distal margin of this segment in S. gracilipes ), the less pronounced posteromedian notch on the telson, and the absence of the rostral carina (cf. Miya, 1972); from S. seticheles by the absence of long, flexible setae on the major chela and numerous other features (cf. Anker, 2003b); from S. colinorum by the carpus of the minor cheliped being subequal to the merus (vs. longer in S. colinorum ); from both S. colinorum and S. cavicolus by the ventrally unarmed rostrum (vs. bearing a subapical tooth in S. colinorum and S. cavicolus ), and the posterior margin of the telson bearing a shallow cleft (vs. straight in S. colinorum and S. cavicolus ) (cf. Felder & Manning, 1986; De Grave, 2004); from S. pusillus , new species, by the absence of subapical tooth on the ventral margin of the rostrum and postrostral tubercle (see below); finally, from S. tafaongae by the much shorter, ventrally unarmed rostrum (vs. elongated rostrum armed with a subapical tooth in S. tafaongae ), and the non-upturned extra-corneal teeth (vs. upturned in S. tafaongae ) (cf. Banner & Banner, 1966a).