Salmoneus pusillus, 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 : 307-310

publication ID	https://doi.org/ 10.5281/zenodo.13245424
persistent identifier	https://treatment.plazi.org/id/03AB572D-FFE8-FFB9-FE94-FD90FEFEDC46
treatment provided by	Felipe
scientific name	Salmoneus pusillus
status	sp. nov.

Treatment

Salmoneus pusillus View in CoL , new species

( Figs. 10 View Fig , 11 View Fig )

Material examined. – Holotype, ovigerous female (CL 2.7, TL 7.6) [minor cheliped lacking, specimen dissected]( ZMMU Ma 5444), South China Sea , Vietnam, Nhatrang Bay, Pyramides, depth 14-16 m, on sand under boulder, SCUBA, coll. I. Marin, 12 May.2004.

Paratypes, 2 ovigerous females (CL 2.9, TL 8.2 and CL 3.0, TL 7.9) [minor cheliped of one specimen dissected, major chelipeds detached]( ZMMU Ma 5445), South China Sea, Vietnam, Nhatrang Bay, bay near lighthouse, depth 15 m, slope, on sand under boulder, SCUBA, coll. I. Marin, 27 Jun.2004 .

Description. – Carapace sparsely setose, without pits, laterally with slight suture starting from lateral margin proximal to base of antenna ( Figs. 10c View Fig ), dorsally with minute postrostral tubercle ( Fig. 10b, c View Fig ). Rostrum relatively long, reaching to distal margin of second segment of antennular peduncle ( Fig. 10c View Fig ), longer than broad at base; ventral margin with more or less conspicuous subapical tooth; lateral margins slightly concave ( Fig. 10b View Fig ); rostral carina inconspicuous. Extra-corneal teeth acute, directed anteromesially; margin between rostrum base and extra-corneal teeth deeply incised, U-shaped ( Fig. 5a). Pterygostomial angle rounded. Eyes without tubercle, partly visible in dorsal and lateral view ( Fig. 10 View Fig ac), sometimes concealed (10h). Epistomial sclerite with strong acute process. Ocellar beak inconspicuous.

Antennular peduncle moderately stout, second segment shorter than visible portion of first segment, and shorter than third segment; ventromesial carina of first segment with acute tooth; stylocerite reaching to distal margin of second segment, distally acute ( Fig. 10b, c View Fig ); lateral flagellum biramous, with shorter ramus situated at second segment. Antenna with basicerite bearing strong ventrolateral tooth ( Fig. 10c View Fig ); scaphocerite subrectangular, anterior margin of blade convex, not exceeding distolateral tooth ( Fig. 10b View Fig ); carpocerite short, reaching to about 3/4 length of scaphocerite ( Fig. 10c View Fig ).

Mouthparts not dissected, appearing typical for genus in external view. Third maxilliped slender; lateral plate large, rounded; ultimate segment distally with small spinules; arthrobranch rather poorly developed.

First pereiopods (chelipeds) very asymmetrical, unequal ( Fig. 10d View Fig , 11 View Fig ), carried flexed ventrally in life; major cheliped ( Fig. 11 View Fig ) slender; ischium elongate, with strong ventral spine ( Fig. 11a View Fig ); merus slender, elongate, distally not widening, ventrally flattened; carpus vase-shaped ( Fig. 11a, c View Fig ), ventrally not depressed, distally with broad lobes ( Fig. 11b, c View Fig ); chela subcylindrical, with palm slightly shorter or subequal to fingers; palm proximoventrally with deep groove, rest of palmar surface smooth; pollex with cutting edge armed with 11-12 rounded-triangular, regularly spaced teeth, distal portion unarmed, tip strongly curved; dactylus with cutting edge bearing 11 teeth, most distal portion unarmed, tip curved ( Fig. 11b, c View Fig ). Minor cheliped slender; ischium elongate, slightly shorter than merus, armed with spine ventrally ( Fig. 10d View Fig ); carpus somewhat longer than merus, subcylindrical, distally slightly widening; chela simple, not particularly enlarged, fingers slightly longer than palm, cutting edges unarmed.

Second pereiopod slender; ischium about 5/6 length of merus, unarmed; carpus with five segments having ratio of approximately 5/2/1/1.2/2.2; chela simple, fingers longer than palm ( Fig. 10e View Fig ). Third pereiopod slender; ischium with two spines ( Fig. 10f View Fig ); merus slender, almost twice as long as ischium, six to seven times as long as wide at base; carpus equally slender, subequal in length to merus, with small distoventral spinule; propodus subequal to carpus, ventrally with three slender spinules and one slender distoventral spine proximal to dactylus; dactylus simple, slender, about half length of propodus, slightly curved ( Fig. 10f View Fig ). Fourth pereiopod generally similar to third. Fifth pereiopod with unarmed ischium; merus longer than carpus; propodus longer than carpus, ventral margin with three spinules and one slender spinule proximal to dactylus, distal half with nine rows of setae ventrolaterally; dactylus similar to that of third pereiopod.

Abdominal segments I-III with posteroventral margins rounded; segment IV with posteroventral margin angular; segments V and VI with posteroventral angles acutely projecting ( Fig. 10a View Fig ); segment VI with acute posterior projection near telson, without articulated plate ( Fig. 10a View Fig ); preanal plate rounded posteriorly. Second pleopod with slender appendix masculina, almost twice as long as appendix interna, with small spines distally. Telson about twice as long as wide proximally; basal width approximately double width of posterior margin; dorsal surface with two pairs of spines situated at some distance from lateral margin, at about mid-length and 3/4 length of telson, respectively ( Fig. 10g View Fig ); posterior margin straight, with two pairs of spines, lateral half length of mesial, and two long, plumose setae medially, between mesial spines ( Fig. 10g View Fig ); anal tubercles absent. Uropods slightly longer than telson; sympodite with acute tooth; diaeresis slightly sinuous; lateral spine small ( Fig. 10a View Fig ). Gill formula typical for genus: see under S. nhatrangensis , new species. Eggs comparatively large and few, e.g., at least 13 (diameter 0.5 x 0.8 mm) in holotype ( Fig. 10a View Fig ), around 16 (diameter 0.4 x 0.5 mm) in one paratype .

Colour. – Semitransparent white, gonads or eggs yellow.

Habitat. – All specimens were collected on sand-mud under boulders at depths of 14-16 m.

Etymology. – Salmoneus pusillus , new species, was so named (pusillus – dwarf, minute) because it is one of the smallestsized members of the genus Salmoneus .

Variation. – The only variation noted is the degree of development of the ventral subapcial tooth on the rostrum, and the degree of exposure of the eyes. In the holotype and one of the paratypes, the rostrum has a small subapical tooth, and the eyes are partly exposed dorsally and laterally ( Fig. 10b, c View Fig ), while in the second paratype, the rostrum is only slightly notched subapically, and the eyes are concealed both dorsally and laterally ( Fig. 10h View Fig ).

Remarks. – Salmoneus pusillus , new species, is closely related to S. gracilipes , S. colinorum , S. falcidactylus , new species, S. alpheophilus , new species (see below), S. cavicolus , S. seticheles . In particular, it appears to be morphologically very close to S. colinorum and S. falcidactylus , new species, and must first be contrasted to these two species. Salmoneus pusillus , new species, may be separated from S. colinorum by the longer stylocerite, reaching the posterior margin of the second segment of the antennular peduncle (vs. reaching only 3/4 of this segment in S. colinorum ); the presence of a minute postrostral tubercle (absent in S. colinorum ); the stouter minor cheliped; and the ischium of both chelipeds armed with a strong spine (vs. unarmed in S. colinorum ) (cf. De Grave, 2004). A further possible difference between S. pusillus , new species and S. colinorum is the size of eggs relative to the body: very large in the first species, much smaller in the second (compare Fig. 10a View Fig and De Grave, 2004, fig. 1A).

Salmoneus pusillus , new species differs from S. falcidactylus , new species, by the less elongated dactylus of the third to fifth pereiopods; the longer stylocerite, reaching the posterior margin of the second segment of the antennular peduncle (vs. reaching only about 1/2 of this segment in S. falcidactylus , new species); the somewhat stouter antennular peduncle; the ischium of both chelipeds armed with a robust spine (vs. unarmed in S. falcidactylus , new species); the rostrum armed with a small subapical tooth ventrally (vs. unarmed in S. falcidactylus , new species); and the posterior margin of the telson straight, without cleft, as in S. falcidactylus , new species (cf. Figs. 9 View Fig and 10-11 View Fig View Fig ). Three of the afore-mentioned features, viz. the straight posterior margin of the telson, the cheliped ischium armed with a spine, and the presence of the ventral subapical tooth on the rostrum, separate S. pusillus , new species, from S. gracilipes . The ischium of the third pereiopod is armed with three spines in S. gracilipes (cf. Miya, 1972), and only two in S. pusillus , new species. Further, S. gracilipes was collected intertidally, while all specimens of the new species were collected from subtidal depths (14-16 m). The status of the ovigerous specimen from Majuro Atoll reported as S. gracilipes by Miya (1984) remains unknown. This specimen markedly differs from S. gracilipes sensu Miya, 1972 and most likely represents S. colinorum .

Salmoneus pusillus , new species, shares the presence of a subapical ventral tooth on the rostrum and a spine on the cheliped ischium with two other species, S. alpheophilus , new species, and S. cavicolus . However, it can be separated from S. alpheophilus , new species, by the differently shaped major chela; the unarmed ischium of the second pereiopod (vs. armed with spines in S. alpheophilus , new species); the straight posterior margin of the telson (vs. with a shallow cleft in S. alpheophilus , new species); the eyestalk without tubercle (vs. with anteromesial tubercle in S. alpheophilus , new species); and also by the smaller size (maximum TL 8.2 mm vs. 13.0 mm); and from S. cavicolus by the broader rostrum and much stouter segments of the antennular peduncle (cf. Felder & Manning, 1986). Furthermore, S. alpheophilus , new species, and S. cavicolus both appear to be infaunal shrimps, dwelling mostly in burrows of other crustaceans (Felder & Manning, 1986; see also below), while all three specimens of S. pusillus , new species, were found free-living on sand-mud, dwelling under large boulders. Salmoneus pusillus , new species, is only distantly related to S. seticheles , differing from this species by numerous features, including the absence of a row of long, flexible setae on the major chela, characteristic of S. seticheles (cf. Anker, 2003b).