Salmoneus arabicus sp. nov.

(Figs. 4–6)

Type material. Holotype, ovig. specimen (cl 2.8 mm), FLMNH UF 35964, Red Sea, Saudi Arabia, off Thuwal, Al Fahal Reef, 22°16'52.2"N, 38°57'45.8"E, exposed side of offshore coral reef, depth: 10–20 m, leg. A. Anker et al., 19.03.2013 [fcn BDJRS-3038]; paratypes: 1 ovig. specimen (cl 3.1 mm), FLMNH UF 35982, Red Sea, Saudi Arabia, northern Farasan Banks off Al-Lith, Whale Shark Reef, 20°07'01.2"N, 40°12'54.0"E, offshore coral reef, depth: 10 m, leg. A. Anker et al., 22.03.2013 [fcn BDJRS-3160]; 1 ovig. specimen (cl 2.9 mm), FLMNH UF 35985, same collection data as for previous paratype [fcn BDJRS-3163].

Description. Small-sized shrimp with moderately slender, non-compressed body. Carapace (Fig. 4a, b) smooth, glabrous, completely covering eyes dorsally, only partly concealing them laterally; anterolateral suture present; pterygostomial angle broadly rounded; cardiac notch deep. Rostrum (Fig. 4a, b) almost perfectly triangular, as long as broad, with acute tip, latter distinctly overreaching distal margin of first article of antennular peduncle; lateral margins straight to faintly convex; rostral carina short, low, not distinct in posterior half of rostrum; ventral margin unarmed. Orbital teeth (Fig. 4a, 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 occupying most of distal surface; anterodorsal margin without triangular process (Fig. 4a, b). Epistomial sclerites each with acute process.

Pleon (Fig. 4c) with pleura of first to fourth pleonite rounded antero- and posteroventrally; fifth pleuron acutely produced posteroventrally; sixth pleonite with acute subtriangular projection flanking base of telson, oblique suture at posteroventral angle not distinct; preanal plate rounded, with depressed median part.

Telson (Fig. 4d) slender, somewhat elongate, subrectangular, tapering distally, about 2.6 times as long as proximal width; dorsal surface with two pairs of stout spiniform setae situated at about 0.5–0.6 and 0.7–0.8 telson length, respectively; posterior margin with two pairs of slender spiniform setae, mesial distinctly longer than lateral, and moderately deep, U-shaped median notch, latter flanked by two long plumose setae.

Antennular peduncle (Fig. 4a, b, e) stout; dorsally visible portion of first article as long as wide; stylocerite stout, with subacute tip, latter reaching or slightly overreaching mid-length of second article; second article very stout, wider than long; lateral antennular flagellum biramous, with fused portion composed of two short subdivisions; shorter free ramus with at least three poorly demarcated subdivisions each furnished with bundle of aesthetascs. Antenna (Fig. 4a, b) with basicerite stout, armed with sharp distoventral tooth; scaphocerite not overreaching antennular peduncle, ovate, almost twice as long as broad; distolateral tooth not reaching anteriorly protruding distal margin of blade; carpocerite short, reaching half-length of scaphocerite; flagellum not particularly thickened, moderately slender.

Third maxilliped (Fig. 4f) slender; coxa with strap-like epipod and rounded lateral plate; antepenultimate article about 3.2 times as long as penultimate article; penultimate article moderately long, about 2.5 times as long as wide; ultimate article relatively short (compared to antepenultimate article), tapering distally, ending in corneous apical tooth, without spiniform setae; exopod well developed, reaching 0.8 length of antepenultimate article; arthrobranch rather small.

First pereiopods = chelipeds (Fig. 5) very different in shape, asymmetrical in size. Major cheliped (Fig. 5a–c) moderately robust, carried flexed under body at rest; ischium slender, about three times as long as wide, armed with one robust spiniform seta on ventrolateral surface; merus long, slender, almost straight, slightly widening distally, about 4.7 times as long as distal width, shallowly depressed ventrally; carpus cup-shaped, short, with rounded distal lobes, without acute or subacute process; chela somewhat enlarged and swollen, slightly longer than merus, with smooth surfaces; palm about 2.2 times as long as maximal width, with deep transverse groove proximo-ventrally, near carpus; fingers about 0.8 length of palm, not gaping when closed, not noticeably twisted, with gently crossing fingertips; cutting edges with about 10–12 rounded teeth in form of almost continuous serration (except for edges near fingertips), proximal-most and distal-most teeth smallest, those near mid-length largest. Minor cheliped (Fig. 5d) much smaller and weaker than major cheliped; ischium about 3.5 times as long as wide, armed with two stout spiniform setae on ventrolateral margin; merus slightly longer than ischium, slightly swollen, about 3.2 times as long as wide; carpus subcylindrical, slightly shorter than merus, widening distally; chela of about same length as carpus; palm as long as fingers, latter simple, with unarmed cutting edges.

Second pereiopod (Fig. 4g) slender; ischium elongate, almost seven times as long as wide, with one spiniform seta on ventrolateral surface, at about 0.3–0.4 of ischial length; merus slightly longer than ischium; carpus with five subarticles, proximal equal to sum of remaining four; length ratio of carpal subarticles approximately equal to 6: 2: 1: 1.5: 2.2.

Third pereiopod (Fig. 4h, i) moderately slender; ischium about 3.5 times as long as wide, with three spiniform setae on ventrolateral surface; merus about 1.4 times as long as ischium, about six 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 four slender spiniform setae on ventral margin and one pair of longer spiniform setae on distoventral margin, near dactylar base; dactylus moderately slender, gently curved, conical, about 0.4 length of propodus. Fourth pereiopod generally similar to third pereiopod, slenderer; ischium with two or three spiniform setae on distoventral margin. Fifth pereiopod (Fig. 4j, k) slenderer than third and fourth pereiopods; ischium about 3.5 times as long as wide, unarmed; merus about seven times as long as maximal width; carpus about as long as merus, much slenderer, with unarmed distoventral margin; propodus about 1.3 times as long as carpus, with four widely spaced spiniform setae along ventral margin and two longer spiniform setae on distoventral margin, near dactylar base; propodal cleaning brush well developed, composed of dozen or so transverse rows of microserrulate setae occupying distal third of propodus; dactylus slender, slightly curved, conical, about 0.3 length of propodus.

Second pleopod with appendix masculina of about same length as appendix interna. Uropod (Fig. 4l) with lateral lobe of protopod produced into sharp tooth; exopod moderately broad, ovate, with long spiniform seta flanked by small subacute distolateral tooth and subtriangular lateral tooth of somewhat sinuous diaeresis; endopod as long as exopod, noticeably narrower, without specific features.

Colour in life. Semi-transparent whitish; yellow-orange inner organs visible due to translucence of carapace; freshly laid eggs bright orange (Fig. 6).

Type locality. Thuwal, Saudi Arabia.

Distribution. Red Sea: presently known only from the reefs off Thuwal and Al-Lith (northern Farasan Banks), Saudi Arabia.

Ecology. The type specimens were collected under coral rubble on offshore coral reefs, at depths of 10–20 m.

Etymology. The new species’ name alludes to Saudi Arabia, the country of the type locality; used as an adjective.

Remarks. Salmoneus arabicus sp. nov. appears to be morphologically closest to S. latirostris, S. nhatrangensis Anker & Marin, 2006, S. serratidigitus, S. teres, S. inconspucuus, S. camaroncito Anker, 2010 and S. saotomensis Anker, 2020, especially in the presence of a basally broad rostrum with a short, not posteriorly extending carina, the dorsally completely or almost completely covered eyes, and the general shape of the chelipeds (Coutière 1899; Manning & Chace 1990; Anker & Marin 2006; Anker 2007, 2010, 2020). However, S. arabicus sp. nov. can be separated from S. latirostris, S. teres and S. inconspicuus by the more triangular rostrum, with the lateral margins almost straight (vs. proximally convex in S. latirostris); from S. latirostris and S. serratidigitus by the uniform whitish colouration (vs. red banded in S. latirostris and bright yellow-orange in S. serratidigitus); from S. nhatrangensis, S. serratidigitus and possibly S. latirostris by the ischia of the major and minor cheliped and the ischium of the second pereiopod armed with spiniform setae (vs. unarmed in the other species, to be confirmed for S. latirostris); from S. teres and S. inconspicuus by the major cheliped armed with a spiniform seta (vs. unarmed in the other two species); from S. serratidigitus, S. teres and S. inconspicuus by the shorter stylocerite, only slightly overreaching the mid-length of the second article of the antennular peduncle (vs. reaching to the end of the second article or beyond it in the other species); from S. nhatrangensis by the much shallower notches between the orbital teeth and the base of the rostrum; from S. teres by the third pereiopod ischium armed with spiniform setae (vs. unarmed in S. teres); from S. camaroncito and S. saotomensis by the minor cheliped non-enlarged and with the chela fingers unarmed (vs. noticeably enlarged and with the chela fingers armed with small teeth in S. camaroncito and S. saotomensis); from S. camaroncito by the rostrum directed forwards, without subdistal tooth on its ventral margin (vs. directed slightly downwards, with a small subdistal tooth, in S. camaroncito); and from S. saotomensis by the major cheliped carpus unarmed ventrally (vs. with a strong ventromesial process in S. saotomensis) (Coutière 1899; Banner & Banner 1981; Manning & Chace 1990; Anker & Marin 2006; Anker 2007, 2010, 2020).

All other species of Salmoneus differ from S. arabicus sp. nov. by a greater number of morphological features and/or colour (where known). This includes all remaining species known from the Red Sea and adjacent areas of the Indian Ocean, e.g. S. rashedi, S. venustus, S. chadwickae and S. cristatus (all with different colourations), as well as the above-described S. farasan sp. nov.