Salmoneus farasan, Anker, 2022

Anker, Arthur, 2022, Three new species of the shrimp genus Salmoneus Holthuis, 1955 from the Red Sea, with a new record of S. poupini Anker, 2010 (Malacostraca: Decapoda Alpheidae), Zootaxa 5138 (3), pp. 261-282 : 262-266

Salmoneus farasan sp. nov.

( Figs. 1–3 )

Type material. Holotype, ovig. specimen (cl 3.7 mm), FLMNH UF 36951 , Red Sea , Saudi Arabia, Farasan Islands, Tiger Head Island, 16°47'27.6"N, 42°11'55.3"E, karstic shore with fringing reef, depth 1–6 m, leg. A. Anker et al., 10.03.2013 [fcn BDJRS-2575].

Description. Small-sized shrimp with moderately slender, non-compressed body. Carapace ( Fig. 1a, b ) smooth, covered by short setae, almost completely concealing eyes dorsally (except for most-anterior portion), partly concealing them laterally; anterolateral suture present; pterygostomial angle broadly rounded; cardiac notch deep. Rostrum ( Fig. 1a, b ) triangular, slightly longer than broad, with acute tip, latter distinctly overreaching distal margin of first article of antennular peduncle; lateral margins slightly concave; rostral carina not distinct; ventral margin unarmed. Orbital teeth ( Fig. 1a, b ) well developed, about 0.2 of rostrum length, narrow, acute, extending well beyond eyes, directed slightly mesially in dorsal view, anteriorly in lateral view.

Eyestalks with cornea slightly reduced, not occupying entire distal surface; anterodorsal margin with small triangular process ( Fig. 1a, b ). Epistomial sclerites each with acute process.

Pleon ( Fig. 1c ) with pleura of first to fourth pleonite rounded antero- and posteroventrally; fifth pleuron acutely produced posteroventrally; sixth pleonite with subacute subtriangular projection flanking base of telson and barely visible oblique suture at posteroventral angle; preanal plate rounded, with median depression.

Telson ( Fig. 1d ) moderately slender, trapezoid, strongly tapering distally, about 2.3 times as long as proximal width; dorsal surface with two pairs of stout spiniform setae situated at about 0.5 and 0.8 telson length, respectively; posterior margin with two pairs of slender spiniform setae, mesial slightly longer than lateral, and small U-shaped median notch, latter with few short plumose setae.

Antennular peduncle ( Fig. 1a, b ) relatively stout; dorsally visible portion of first article as long as wide; stylocerite narrow, with subacute tip, latter distinctly overreaching mid-length of second article; ventromesial carina with small tooth; second article quadrate, about as long than wide; lateral antennular flagellum biramous, with fused portion composed of three short subdivisions; shorter free ramus with five or so poorly demarcated subdivisions each furnished with bundle of aesthetascs. Antenna ( Fig. 1a, b, e ) with basicerite stout, armed with prominent sharp distoventral tooth; scaphocerite not overreaching antennular peduncle, ovate, almost twice as long as broad; distolateral tooth falling short of distal margin of blade; carpocerite short, reaching half-length of scaphocerite; flagellum not particularly thickened, moderately slender.

Third maxilliped ( Fig. 1f ) slender; coxa with strap-like epipod and prominent, almost rounded lateral plate; antepenultimate article about 2.8 times as long as penultimate article; penultimate article moderately long, about three times as long as wide; ultimate article tapering distally, ending in corneous apical tooth, without spiniform setae; exopod well developed, almost reaching distal margin of antepenultimate article; arthrobranch normally developed, not enlarged.

First pereiopods = chelipeds ( Fig. 2 ) very different in shape, asymmetrical in size. Major cheliped ( Fig. 2a–d ) moderately robust, carried flexed under body at rest; ischium slender, about 3.5 times as long as wide, armed with one spiniform seta on ventrolateral surface; merus long, slender, almost straight, conspicuously widening distally, about four times as long as distal width, depressed ventrally; carpus cup-shaped, short, with blunt distal lobes, without acute or subacute process; chela enlarged, moderately swollen, as long as merus and ischium combined, with smooth surfaces; palm about twice as long as maximal width, somewhat flattened dorsally, with deep transverse groove proximo-ventrally; fingers about as long as palm, not gaping when closed, not noticeably twisted, with crossing fingertips; cutting edges with about 20 small rounded teeth in form of almost continuous serration (except for edges near fingertips), distal-most teeth smaller. Minor cheliped ( Fig. 2e, f ) much smaller and weaker than major cheliped, slender; ischium elongate, four times times as long as wide, armed with one spiniform seta on ventrolateral margin; merus slightly longer than ischium, slightly curved, not swollen, about five times as long as wide; carpus slender, subcylindrical, slightly longer than merus, widening distally; chela about 0.6 length of carpus; palm as long as fingers, latter simple, with each cutting edge armed with three minute teeth in distal half.

Second pereiopod ( Fig. 1g ) slender; ischium elongate, almost seven times as long as wide, with one spiniform seta on ventrolateral surface, at about 0.3 of ischial length; merus slightly longer than ischium; carpus with five subarticles, proximal subarticle slightly longer than combined length of remaining ones; length ratio of carpal subarticles approximately equal to 5.5: 1.5: 1: 1: 1.8.

Third pereiopod ( Fig. 1h ) moderately slender; ischium elongate, about four times as long as wide, with two spiniform setae on ventrolateral surface; merus about 1.3 times as long as ischium, about five times as long as maximal width; carpus distinctly slenderer and shorter than merus, with small spiniform seta on distoventral margin; propodus subequal to carpus in length, with three widely spaced, short spiniform setae on ventral margin and one pair of longer spiniform setae distally, near dactylar base; dactylus relatively slender, gently curved, conical, about half-length of propodus. Fourth pereiopod generally similar to third pereiopod, slenderer. Fifth pereiopod ( Fig. 1i, j ) slenderer than third and fourth pereiopods; ischium about three times as long as wide, unarmed; merus about six times as long as maximal width; carpus as long as merus, slenderer, with small spiniform seta on distoventral margin; propodus about 1.5 times as long as carpus, with six widely spaced, shorter or longer spiniform setae along ventral margin and two long spiniform setae on distoventral margin, near dactylar base; propodal cleaning brush moderately developed, composed of seven or so transverse rows of microserrulate setae; dactylus slender, conical, about 0.4 length of propodus.

Second pleopod with appendix masculina of about same length as appendix interna ( Fig. 1k ). Uropod ( Fig. 1l ) with lateral lobe of protopod produced into sharp slender tooth; exopod moderately broad, ovate, with slender spiniform seta flanked by small subacute distolateral tooth and subtriangular lateral tooth of dome-shaped diaeresis; endopod as long as exopod, slightly narrower, without specific features.

Colour in life. Semi-transparent whitish; major chela hyaline white; pale yellow and brown inner organs visible due to translucence of carapace; freshly laid eggs pale orange ( Fig. 3 ).

Type locality. Farasan Islands , Saudi Arabia .

Distribution. Red Sea: currently known only from the type locality in the Farasan Islands, Saudi Arabia.

Ecology. The holotype was collected under a large piece of coral rubble deeply immerged in sand near an abrupt karstic wall of a small islet, at a depth of 1–6 m.

Etymology. The new species is named after the type locality, the Farasan Islands, in the southern Red Sea. Used as a noun in apposition.

Remarks. Salmoneus farasan sp. nov. displays features of two of seven informal species groups tentatively established by Anker & Marin (2006); however, neither of these two groups appears to represent a monophyletic group. In the general shape of the chelipeds and frontal area, including the shape of the rostrum and the proportions of the antennular peduncles, S. farasan sp. nov. is closest to the S. serratidigitus species group, especially S. latirostris , S. mauiensis ( Edmondson, 1930) , S. sibogae ( De Man, 1910) , S. kekovae Grippa, 2004 , S. teres Manning & Chace, 1990 and S. inconspicuus Anker, 2020 ( Coutière 1897, 1899; De Man 1910, 1911; Edmondson 1930; Manning & Chace 1990; Grippa 2004; Anker 2020). On the other hand, in the armature of the cheliped ischia and partial exposure of the eyes, the new species is closer to some species referred to the S. gracilipes species group, such as S. pusillus Anker & Marin, 2006 and S. ikaros ( Anker & Marin 2006; Anker et al. 2020).

Salmoneus farasan sp. nov. can be separated from S. sibogae , S. latirostris , S. mauiensis and S. ikaros by the distinctly shorter stylocerite, the latter not reaching the distal margin of the second article of the antennular peduncle (vs. reaching or exceeding this margin in the other species); from S. sibogae , S. latirostris , S. mauiensis , S. teres and S. pusillus by the second article of the antennular peduncle as long as wide (vs. much wider than long in the other species); from S. kekovae by the presence of spiniform setae on the cheliped ischia and the much less inflated major chela, the latter also with more numerous teeth on the finger cutting edges (around 20 in S. farasan sp. nov. vs. not exceeding 10 in S. kekovae ); from S. latirostris , S. teres and S. inconspicuus by the lateral margins of the rostrum broadly concave (vs. slightly convex proximally in the other species); from S. sibogae by the dorsally partly exposed eyes (vs. completely covered dorsally in S. sibogae ) and much shallower, more U-shaped median notch on the posterior margin of the telson (vs. deeper and almost V-shaped in S. sibogae ); from S. mauiensis by the much more numerous teeth on the cutting edges of the major chela (around 20 in S. farasan sp. nov. vs. only four in S. mauiensis ); from S. pusillus by the absence of a small post-rostral tubercle on the carapace (present in S. pusillus ); and from S. ikaros by the eye cornea not especially modified (vs. with two distinct areas and a peculiar dendritic structure in S. ikaros ); and from S. latirostris , S. mauiensis and S. kekovae by the uniform whitish colouration (vs. red-banded in S. latirostris or bright yellow to orange in S. mauiensis and S. kekovae ) ( Coutière 1899; De Man 1911; Edmondson 1930; Banner 1953; Banner & Banner 1985; Manning & Chace 1990; Grippa 2004; Anker & Marin 2006; Anker 2020; Anker et al. 2020).

All other known species of Salmoneus seem to be more distant to S. farasan sp. nov. and can be easily separated by at least three (and usually more) morphological characters, involving, for instance, the presence of a rostral carina (which is absent in the new species); the proportions of the dactylus of the third to fifth pereiopods; the development of the post-rostral tubercle on the carapace (which is absent in the new species); the shape and size of the rostro-orbital area; the shape of the telson (especially of the posterior margin); and the degree of asymmetry and general shape and armature of the chelipeds. This includes all other species of Salmoneus presently known from the north-western Indian Ocean, namely S. brevirostris , S. chadwickae , S. cristatus , S. venustus , S. gracilipes , S. durisi and S. rashedi ( Coutière 1897, 1899; Kazmi 1974; Banner & Banner 1981; Ďuriš & Horká, 2016; Anker 2019; Anker & Ashrafi 2019; Anker et al. 2020), as well as several non-identified species listed by Ďuriš & Horká (2016). However, it must be noted that the record of S. brevirostris from Pakistan by Kazmi (1974) is quite problematic due to highly diagrammatic and possibly inaccurate illustrations, whereas the two specimens reported as S. gracilipes from Kuwait differ in some morphological details from each other and from the type material from Japan, and therefore may not represent S. gracilipes sensu Miya (1972) (see also Anker et al. 2020).

Figures

FIGURE 1. Salmoneus farasan sp. nov., holotype, ovigerous specimen (cl 3.7 mm) from the Farasan Islands, Saudi Arabia (FLMNH UF 36951): a—frontal region, dorsal; b—same, lateral view; c—fourth, fifth and sixth pleonites, lateral; d—telson, lateral; e—antennal scaphocerite, dorsal; f—third maxilliped, lateral; g—second pereiopod, lateral; h—third pereiopod, lateral; i—fifth pereiopod, lateral; j—same, propodus and dactylus, mesial; k—second pleopod, detail of appendix masculina and appendix interna, anterior; l—uropod, dorsal.

FIGURE 2. Salmoneus farasan sp. nov., holotype, ovigerous specimen (cl 3.7 mm) from the Farasan Islands, Saudi Arabia (FLMNH UF 36951): a—major (right) cheliped, lateral; b—same, mesial; c—same, carpus and chela, dorsomesial; d—same, chela fingers, dorsomesial; e—minor (left) cheliped, lateral; f—same, carpus and chela, mesial.

FIGURE 3. Salmoneus farasan sp. nov., holotype, ovigerous specimen (cl 3.7 mm) from the Farasan Islands, Saudi Arabia (FLMNH UF 36951): a—shrimp in life, dorsal; b—same, lateral. Photographs by the author.