A New Species of the Shrimp Genus Salmoneus Holthuis, 1955 (Malacostraca: Decapoda: Alpheidae) from the Exposed Shores of Eastern and Southern Oman †

: Salmoneus sultanus sp. nov. is described based on several specimens collected on the exposed shores of Masirah Island and Dhofar, Oman, a region characterised by seasonal upwellings cooling water temperature to less than 23 ◦ C. The new species is compared with the morphologically most similar congeners present in the north-western Indian Ocean, e.g., S. latirostris (Couti è re, 1897), S. cristatus (Couti è re, 1897), S. serratidigitus (Couti è re, 1897), and S. chadwickae ˇDuriš and Hork á , 2016; the latter species is recorded for the first time from Oman. The conspicuous colour pattern of S. sultanus sp. nov. appears to be diagnostic, differing greatly from that of S. latirostris , S. cristatus , S. serratidigitus , and S. chadwickae .

In January and November 2022, several specimens of a brightly coloured species of Salmoneus were collected in the shallow waters of Mirbat, the Dhofar Governorate of Oman, and near the southern tip of Masirah Island, Ash Sharqiyah South Governorate of Oman, respectively.The diagnostic colour of the specimens suggested that they may belong to an undescribed species, which was confirmed by examination of the material and its comparison with all morphologically similar species.Therefore, in the present study, a new species of Salmoneus is described based on the aforementioned material from Oman.

Materials and Methods
The herein reported specimens were collected during two BioBlitz surveys in Oman in 2022 (see Acknowledgments).All shrimps were collected with a dip net while snorkelling in very shallow water (less than 1 m) at low tide.Type material was deposited in the collections of the Florida Museum of Natural History, University of Florida, Gainesville, FL, USA (FLMNH).The carapace length (cl, in mm) was measured from the tip of the rostrum to the posterior margin of the carapace.Comparative material used in this study, collected in Oman and Saudi Arabia in 2022, is listed below.

Taxonomy
Family Alpheidae Rafinesque, 1815 [16] Genus Salmoneus Holthuis, 1955 [ Description.Moderately sized species of Salmoneus (type material: cl 4.6-5.8mm).Carapace (Figure 1A,B) densely covered with erect setae; pterygostomial angle broadly rounded; cardiac notch deep.Rostrum (Figure 1A,B) subtriangular in dorsal view, horizontal in lateral view, 1.2 times as long as wide at base (measured between orbital notches) acute distally; tip reaching, almost reaching, or slightly overreaching distal margin of second article of antennular peduncle; lateral margins slightly convex in proximal half; dorsal carina distinct only in distal half, fading before reaching eye level; ventral carina without tooth; post-rostral tubercle.Orbital teeth (Figure 1A,B) moderately developed, about 0.2 of rostrum length, subtriangular, acute distally, slightly turned mesially, not extending beyond eyes; shape of orbital notches intermediate between V and U.Each epistomial sclerite with short blunt process.
Pleon (Figure 1C) patchily covered with erect setae; pleura of first to fifth pleonite rounded posteroventrally, that of fifth pleonite more angular; sixth pleonite not particularly elongate, with subacute projection flanking telson on posterior margin and barely discernible suture separating posteroventral angle; however, not forming articulated plate; preanal plate broadly rounded.Telson (Figure 1D,E) moderately stout, subrectangular, distinctly tapering distally, about 2.2 times as long as proximal width; dorsal surface covered with setae and armed with two pairs of stout spiniform setae situated at about 0.5 and 0.8 telson length, respectively, posterior pair located closer to lateral margin than anterior pair; posterior margin with two pairs of elongate spiniform setae, mesial almost twice as long as lateral, and broad V-shaped median notch, latter furnished with row of several plumose setae and with one stiff seta near each lateral margin.
Eyes (Figure 1A,B) partly exposed dorsally and largely exposed laterally, with only most proximal part of eyestalks concealed by base of rostrum and orbital teeth; cornea not particularly reduced, normally pigmented; anterodorsal margin rounded.
Antennular peduncle (Figure 1A,B,F) very stout; stylocerite stout, broad, with subacute tip, latter reaching or slightly overreaching distal margin of second article; ventromesial carina with anteriorly directed, sharp tooth; second article about 0.9 times as long as wide; third article slightly longer than second; lateral antennular flagellum with fused portion composed of three subdivisions; accessory (free) ramus with poorly demarcated subdivisions bearing seven or so groups of aesthetascs.Antenna (Figure 1A,B,G) with basicerite stout, armed with large, sharp, distoventral tooth; scaphocerite not reaching distal end of antennular peduncle, with moderately strong distolateral tooth, latter not reaching beyond anterior margin of broad blade; carpocerite stout, short, reaching half-length of scaphocerite; flagellum long, not particularly thickened.
Mouthparts typical for genus in external view.Third maxilliped (Figure 1H) slender; coxa with strap-like epipod (mastigobranch) and rounded lateral plate; antepenultimate article about 0.4 length of antepenultimate article, distally widening, almost three times as long as distal width; penultimate article more than twice as long as penultimate article, strongly tapering distally, apex in form of subacute corneous point, without spiniform setae; exopod well developed, however, not reaching end of antepenultimate article; arthrobranch normally developed.
First pereiopods = chelipeds (Figure 2) very different in size, asymmetrical in shape, carried folded at rest.Major cheliped (Figure 2A-C) moderately long and robust; ischium unarmed, somewhat depressed ventrally; merus long, slender, distally widening, about 5.5 times as long as distal width (height), depressed ventrally, with smooth margins; carpus cup-shaped, distally wider, with several blunt lobes distoventrally; chela moderately swollen, subcylindrical, longer than merus and ischium combined, smooth; palm about twice as long as maximal width, about 0.9 of merus length, smooth, with deep, complex groove ventroproximally; fingers about 0.8 length of palm, slightly twisted, pollex slightly longer than dactylus, fingertips strongly curved, crossing subapically; cutting edges of pollex and dactylus serrated on almost entire length (except for proximal and distal one-tenths), with 12-13 rounded-subtriangular teeth, proximal-most smallest.Minor cheliped (Figure 2D,E) much smaller and weaker than major cheliped, slender; ischium stout, almost four times as long as wide, unarmed; merus 1.6 times as long as ischium, about five times as long as maximal width; carpus subcylindrical, about 1.1 times as long as merus, distally widening; chela about 0.7 of carpus length; fingers slightly shorter than palm, simple, slightly gaping, with unarmed cutting edges.Second pereiopod (Figure 1I) moderately slender; ischium elongate, about six times as long as wide, unarmed; merus 1.5 times as long as ischium; carpus with five subarticles; first longer than combined length of remaining four, approximate length ratio of carpal subarticles: 6.0:1.2:1:1:2.0.Third pereiopod (Figure 1J,K,R) moderately stout; ischium about 2.5 times as long as distal width, unarmed or with one small spiniform seta on Second pereiopod (Figure 1I) moderately slender; ischium elongate, about six times as long as wide, unarmed; merus 1.5 times as long as ischium; carpus with five subarticles; first longer than combined length of remaining four, approximate length ratio of carpal subarticles: 6.0:1.2:1:1:2.0.Third pereiopod (Figure 1J,K,R) moderately stout; ischium about 2.5 times as long as distal width, unarmed or with one small spiniform seta on ventrolateral surface; merus somewhat swollen, with slightly convex ventral and dorsal margins, about 1.8 times as long as ischium, about four times as long as maximal width; carpus much slenderer than merus, about 0.65 length of merus, distoventrally with short spiniform seta; propodus subequal to carpus in length, ventral margin armed with three widely spaced spiniform setae, distoventral margin adjacent to dactylar base with one pair of spiniform setae, lateral longer and stouter; dactylus about 0.4 of propodus length, moderately slender, about 5.5 times as long as broad at base, gently curved, conical, simple.Fourth pereiopod (Figure 1L) generally similar to third pereiopod, noticeably shorter and slenderer; merus not swollen, about 4.2 times as long as wide; propodus distinctly longer than carpus, ventral margin armed with four spiniform setae, in addition to one distal pair of spiniform setae adjacent to dactylar base; dactylus similar to that of third pereiopod.Fifth pereiopod (Figure 1M-O) much slenderer than third and fourth pereiopods; ischium short, 1.8 times as long as broad, unarmed; merus about 2.3 as long as ischium, almost 4.5 times as long as wide; carpus 0.9 length of merus, slightly slenderer than merus; propodus 1.5 times as long as carpus, ventromesial margin with four or five widely spaced spiniform setae, in addition to one long distal spiniform seta adjacent to dactylar base; propodal grooming brush well developed, composed of 14 or so transverse rows of microserrulate setae extending from about mid-length of article to its distal end; dactylus slightly less than 0.3 length propodus, otherwise similar to those of third and fourth pereiopods.
Second pleopod with appendix masculina much longer than appendix interna (Figure 1P), not exceeding distal margin of endopod; appendix masculina furnished with slender spiniform setae along inner (mesial) margin and on apex.Uropod (Figure 1Q) with lateral lobe of protopod distally produced as small acute tooth; exopod moderately broad, ovate, with small distolateral tooth adjacent to stout spiniform seta; diaeresis sinuous, with blunt lateral tooth; endopod as long as exopod, slightly narrower, without diagnostic features.
Colour pattern.Body largely bright red, with some colourless areas on carapace, for instance, around postorbital area and near branchiostegial and posterior margins, and colourless patches on flanks of some pleonites; red chromatophores on pleon forming diffuse transverse bands; antennular peduncle and antennal scaphocerite with red markings, flagella with purplish tinge distally; major and minor cheliped hyaline white; remaining pereiopods whitish; pleopods with pale red pleopods and whitish exopods and endopods; telson and uropods deep red; eggs or ovaries dark orange red (Figures 3 and 4).
Etymology.The specific epithet refers to the Sultanate of Oman, which is governed by a Sultan (Latin noun sultanus); used as a noun in apposition.
Distribution.Presently known from two localities in Oman, southern tip of Masirah Island (type locality: holotype and one of the paratypes) and Mirbat, Dhofar (remaining paratypes).
Ecology.All specimens were collected under large rocks in fine sand, sometimes with a significant silt component, at depths not exceeding 0.5 m at low tide (about 1-1.5 m at high tide).
The specimen from Red Sea coast of Saudi Arabia, which is herein reported as S. latirostris (Figure 5), corresponds well to the very brief and superficial description provided by Coutière (1897) [5], with a few figures published in Coutière (1899) [6].Furthermore, this specimen has a red-banded colour pattern, as observed by Coutière (1899) [6] in Djibouti.This species awaits a full redescription; however, due to time constraints the author was able to prepare line drawings of the frontal region and major cheliped only (Figure 2F,G), for purely comparative purposes.The species will be eventually redescribed, although it would be better to wait until more material from the Red Sea and Gulf of Aden becomes available.Nevertheless, S. sultanus sp.nov.can be separated from S. latirostris (based on the present specimen and Coutière's (1897 [5], 1899 [6] accounts) by the welldemarcated rostral carina (which is very faint in S. latirostris, cf.Figures 1a and 2f; see also Coutière 1899 [6]: Figure 21); the slightly longer stylocerite, reaching the distal margin of the second article of the antennular peduncle (vs.falling well short of this margin in S. latirostris, cf.Figures 1a and 2f); the ischium of the minor cheliped and second pereiopod unarmed (vs. each armed with one stout spiniform seta in S. latirostris, A. Anker, pers.obs., see also Figures 1I and 2D); the second pereiopod carpus with the second to fourth subarticles being about equal in length (vs.with the second distinctly longer than the third or fourth in S. latirostris, cf. Figure 1I and Coutière 1899 [6]: Figure 299); the third pereiopod merus quite stout, at most four times as long as greatest width (vs.rather slender, almost five times as long as wide, in S. latirostris, cf.Figures 1J and 5B); and the third pereiopod ischium unarmed or armed with very small seta (vs.armed with two strong spiniform setae in S. latirostris, A. Anker, pers.obs., see also Figure 1J,R).The major chelae of the two species appear to be very similar, including the number of teeth on the serrated finger cutting edges (cf. Figure 2C,G).
The type species of Salmoneus, S. serratidigitus, was briefly described by Coutière (1897) [5], with some figures published in Coutière's (1899) [6] famous alpheid monograph.Banner and Banner (1981) [9] published a lengthy account on the results of their search for Coutière's type specimens of Salmoneus in European and US museums.These authors concluded that the original type specimens of S. serratidigitus, S. latirostris, S. cristatus, and also J. De Man's S. sibogae were probably lost.Nevertheless, they provided a detailed description and illustrations of a specimen from Djibouti (Museum of Comparative Zoology, Harvard University, MCZ 5556) personally collected and identified by H. Coutière as S. serratidigitus (Banner and Banner 1981 [9]: Figure 8a-i).These illustrations (but not Banner and Banner 1981 [9]: Figure 7a-g), should be used for any interspecific comparisons involving S. serratidigitus until a highly desirable redescription of the species.Salmoneus sultanus sp.nov.can be easily separated from S. serratidigitus by the shape of the rostrum, which is broader and with lateral margins slightly convex in the proximal half in the new species (vs.narrower and with lateral margins broadly concave throughout in S. serratidigitus); the eyes partly visible in dorsal view (vs.entirely concealed dorsally in S. serratidigitus); the posterior margin of the telson with a broadly V-shaped notch (vs.with a narrower and more U-shaped notch in S. serratidigitus); and the ischia of the third and fourth pereiopods either unarmed or armed with one very small spiniform seta (vs.armed with up to three strong spiniform setae in S. serratidigitus) (cf. Figure 1A,D,E,J,L,R; Banner and Banner 1981 [9]: Figure 8a,g-i).Using essentially the same criteria, the new species from Oman can be distinguished from S. sibogae (currently in the synonymy of S. serratidigitus, but possibly valid, see Anker and De Grave 2016 [32]), except for the posterior margin of the telson, which is very similar between these two species (cf.De Man 1911(1915) [19]: Figure 9).Salmoneus sultanus sp.nov.can be easily distinguished from S. mauiensis by the general shape of the rostrum (see under S. serratidigitus); the stylocerite reaching to the distal margin of the second article of the antennular peduncle (vs.by far overreaching this margin in S. mauiensis); the second article for the antennular peduncle subquadrate, as long as wide (vs.much wider than long in S. mauiensis); and the major chela fingers with 11-12 teeth (vs.with only 7-8 teeth in S. mauiensis) (cf.Figures 1A and 2C; Banner 1953 [21]: Figure 2).The new species also differs from the recently described S. farasan and S. arabicus, for instance, from the former species by the major and minor cheliped ischium being unarmed (vs.armed with one spiniform seta in S. farasan) and several features of the third pereiopod, including the armature of the ischium and relative proportions of the merus, propodus and dactylus (cf.Figures 1J and 2A,B; Anker 2022 [2]: Figures 1h and 2a,e), and from the latter species by the much longer stylocerite, reaching the distal margin of the second article of the antennular peduncle (vs.slightly overreaching the mid-length of this article in S. arabicus), and the armature of the ischium of the chelipeds and second and third pereiopods (cf.Figures 1A,I,J and 2A,B; Anker 2022 [2]: Figures 4a,g,h and 5b).Furthermore, S. sultanus sp.nov.can be easily discriminated from S. hilarulus by the different proportions of the third pereiopod dactylus (which is unusually stout in S. hilarulus), and from S. nhatrangensis by the rather normal configuration of orbital notches (which are very deep and peculiarly shaped in S. nhatrangensis) (cf.De Man 1911 (1915) [19]; Anker and Marin 2006 [17]).
Salmoneus sultanus sp.nov.differs from the eastern Atlantic S. kekovae and the western/central Atlantic S. setosus, S. rocas (possibly junior synonym of S. setosus), S. teres, and S. inconspicuus by several important morphological features, for example, from S. kekovae by the shape of the rostrum and telson, as well as the armature of the finger cutting edges of the major chela and third pereiopod ischium (cf.Grippa 2004 [23]); from S. setosus and S. rocas by the configuration of the rostrum and telson, and the relative proportions of the antennular parts, including the length of the stylocerite (cf.Manning and Chace 1990 [22]; Anker 2007 [24]); from S. teres and S. inconspicuus by the armature of the second pereiopod and configuration of the posterior margin of the telson; and specifically from S. inconspicuus also by the armature of the major and minor chelipeds and third pereiopod (cf.Manning and Chace 1990 [22]; Anker 2020 [27]).
The moderately developed, short rostral carina of S. sultanus sp.nov.can be used to separate the new species from all species with a well-developed rostral carina, often continuing posteriorly and sometimes reaching the posterior fourth of the carapace, including S. cristatus and S. chadwickae, which are distributed from the Red Sea to Iran, and S. auroculatus Anker andMarin, 2006 (Coutière 1899 [6]; Banner and Banner 1981) [9]; Anker and Marin 2006 [17]; Ďuriš and Horká, 2016 [10]).