Salmoneus singularis, Komai & Maenosono & Naruse, 2021

Komai, Tomoyuki, Maenosono, Tadafumi & Naruse, Tohru, 2021, A new species of alpheid shrimp tentatively assigned to Salmoneus Holthuis, 1955 (Decapoda: Caridea) from the Ryukyu Islands, Japan, Zootaxa 4920 (2), pp. 287-296 : 288-294

publication ID	https://doi.org/ 10.11646/zootaxa.4920.2.9
publication LSID	lsid:zoobank.org:pub:901B8453-CC3C-4C59-894C-7052186B46EF
DOI	https://doi.org/10.5281/zenodo.4520063
persistent identifier	https://treatment.plazi.org/id/22FD59C2-669E-45EA-9B56-E4FC55F2C0A5
taxon LSID	lsid:zoobank.org:act:22FD59C2-669E-45EA-9B56-E4FC55F2C0A5
treatment provided by	Plazi
scientific name	Salmoneus singularis
status	sp. nov.

Treatment

Salmoneus singularis n. sp.

[New Japanese name: Kawari-nokogiri-teppou-ebi]

( Figs. 1–5 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 )

Material examined. Holotype: CBM-ZC 16164, non-ovigerous specimen (cl 5.4 mm), NE point of Uchipanari Islet , Iriomote Island , Yaeyama Group, southern Ryukyu Islands, 24.3646°N, 123.7260°E, lower intertidal, seagrass bed, extracted from soft sediments, yabby pump, coll. T. Maenosono, 14 May 2014. GoogleMaps

Paratypes. Same data as holotype: RUMF-ZC-5923, 1 non-ovigerous specimen (cl 3.7 mm); CBM-ZC 16165, 1 ovigerous female (cl 5.8 mm).

Diagnosis. Medium-sized species of Salmoneus (cl of ovigerous specimen 5.8 mm), with moderately slender body. Rostrum 0.3–0.4 times as long as carapace, reaching or overreaching distal end of article 2 of antennular peduncle, narrowly triangular in dorsal view; mid-dorsal carina obsolete; ventral margin with 1 minute subterminal spine. Carapace with strong postorbital spine on each side; orbital spine reduced to small, bluntly triangular projection. Telson with deep, V-shaped, posteromedian notch. Eyes mostly covered by carapace in dorsal view, with only anterolateral part of cornea visible; eyestalk with minute distomesial projection; cornea moderately developed. Antennule with stylocerite strong, reaching mid-length of peduncular article 2. Antenna with carpocerite short, reaching mid-length of scaphocerite. Maxilliped 3 with lateral plate strongly produced dorsally, subacutely pointed. Chelipeds greatly unequal and dissimilar. Major cheliped with ischium unarmed; merus slender, elongate, mesioventrally flattened; palm subcylindrical, not particularly inflated, without grooves; fingers slightly shorter than palm, occlusal margins with 15–16 blunt triangular teeth over entire length. Minor cheliped much smaller and shorter than major cheliped; ischium with 1 spiniform seta; carpus subequal in length to merus; chela shorter than carpus. Pereopod 2 slender; ischium with 2 spiniform setae. Pereopods 3–5 slender; ischium of pereopods 3 and 4 each with 3 spiniform setae; dactylus very slender, exceeding half-length of propodus in pereopods 3 and 4. Second pleopod with appendix masculina elongate, almost reaching distal margin of endopod.

Description. Holotype. Body moderately stout for genus ( Fig. 1 View FIGURE 1 ).

Rostrum ( Fig. 2A, B View FIGURE 2 ) relatively long, 0.3 times as long as carapace, overreaching distal margin of article 2 of antennular peduncle, dorsoventrally flattened, narrowly triangular in dorsal view, distinctly longer than wide at base, nearly horizontal in lateral view, without distinct mid-dorsal carina; dorsal margin slightly sloping toward tip; lateral margins faintly concave in dorsal view; tip acute; ventral surface sharply carinate medially, with minute subapical spine. Carapace ( Figs. 1 View FIGURE 1 , 2A, B View FIGURE 2 ) slightly inflated dorsally, surface glabrous, armed with 1 pair of dorsolateral spines in postorbital position; dorsal mid-line without tubercle or spine; cardiac notch moderately deep; orbital spine reduced to small, bluntly triangular projection; anterolateral margin below orbital teeth broadly sinuous; pterygostomial angle broadly rounded.

Pleon ( Fig. 1 View FIGURE 1 ) with anterior 3 pleura rounded posteroventrally; pleuron 4 pointed at posteroventral angle, not acute; pleuron 5 with minute posteroventral spine. Pleomere 6 1.2 times as long as high, without articulated posteroventral plate, with faint suture; preanal plate rounded; posterolateral process short, terminating acutely. Telson ( Fig. 2C View FIGURE 2 ) moderately slender, tapering distally, 2.6 times as long as maximal (proximal) width; dorsal surface with 2 pairs of small spiniform setae both inserted at some distance from lateral margin, first pair at about telson mid-length, second pair at about 0.7 of telson length; posterior margin with deep V-shaped notch, remaining lateral portions straight, each bearing 2 unequal spiniform setae, mesial much stouter and about 1.3 times longer than lateral.

Eyestalks ( Fig. 2A, B, D View FIGURE 2 ) mostly concealed by anterior part of carapace, with minute dorsomesial distal tubercle; anterolateral part of cornea visible in dorsal view; cornea located at anterolateral part of eyestalk, darkly pigmented.

Antennular peduncle ( Fig. 2A, B View FIGURE 2 ) stout. Article 1 with small, anteriorly directed tooth on ventromesial ridge; stylocerite slender, with acute tip reaching beyond mid-length of article 2, its dorsal margin sharply carinate and broadly convex in lateral view. Article 2 subquadrate, 1.1 times as long as wide, slightly overreaching distal end of antennal scaphocerite. Lateral flagellum ( Fig. 2A View FIGURE 2 ) biramous, with fused portion very short; secondary ramus composed of 4 units with several groups of long aesthetascs.

Antenna ( Fig. 2A, B, E View FIGURE 2 ) with basicerite bearing small, ventrolateral distal spine; dorsomesial margin broadly bilobed distally, mesial lobe overhanging base of scaphocerite. Scaphocerite subovate with nearly straight lateral margin and gently convex mesial margin; distal blade broadly rounded, reaching slightly beyond small distolateral spine. Carpocerite short, stout, reaching mid-length of scaphocerite.

Epistomial sclerites each with short protuberance. Upper lip with crested median lobe.

Mouthparts typical for genus in external observation (not illustrated).

Maxilliped 3 ( Figs. 3A View FIGURE 3 , 5A, B View FIGURE 5 ) moderately slender, reaching distal margin of antennal scaphocerite. Coxa with lateral plate rounded-subquadrate. Antepenultimate article sinuously curved, proximal half flattened dorsoventrally. Penultimate article slightly widened distally. Ultimate article tapering distally from mid-length to acute tip, with 1 prominent subterminal seta; mesial face with several transverse tracts of stiff serrulate setae.

Pereopods 1 (chelipeds) strongly unequal in size and asymmetrical in shape; major (right) cheliped exceeding twice length of minor (right) cheliped, much more robust.

Major cheliped ( Fig. 4 View FIGURE 4 A–E) elongate, relatively slender, in full extension overreaching distal margin of antennal scaphocerite by length of chela and carpus. Ischium nearly straight, without spiniform seta; ventrolateral margin bluntly carinate. Merus fairly depressed dorsoventrally, slightly arcuate, slightly widened distally, about twice length of ischium; ventral surface shallowly concave to accommodate flexor surface of chela. Carpus short, widened distally, cup-shaped; distomesial margin produced into blunt projection. Chela 0.75 times as long as carapace, subcylindrical, smooth, without grooves, mesial margin gently sinuous; palm 3 times as long as wide; fingers not particularly elongate, 0.9 times as long as palm, strongly compressed; fingertips strongly curved, crossing, acuminate; occlusal margin of dactylus with 15 narrowly spaced, small, subtriangular, distally subacute or rounded teeth along its entire length; occlusal margin of pollex with 16 teeth similar to those of dactylus.

Minor cheliped ( Fig. 3B, C View FIGURE 3 ) in full extension reaching mid-length of scaphocerite by tip of chela. Ischium with 1 spiniform seta at mid-length of ventrolateral surface. Merus 1.3 times as long as ischium. Carpus subequal in length to merus, widened distally, 5 times as long as distal width. Chela 0.8 times as long as carpus; palm slightly depressed; fingers subequal to palm in length, not crossing distally, cutting edges unarmed, forming thin blade.

Pereopod 2 ( Fig. 3D View FIGURE 3 ) slender, moderately long, distinctly longer than minor cheliped, not reaching distal margin of scaphocerite. Basis unarmed. Ischium with 2 spiniform setae on lateral surface ventrally. Merus slightly longer than ischium. Carpus about 0.7 times as long as ischium and merus combined, subdivided into 5 articles, ratio of carpal subarticles from proximal to distal equal to: 3.1: 0.7: 0.5: 0.5: 1.0. Chela 1.8 times as long as distal-most carpal subarticle; dactylus 1.7 times as long as palm.

Pereopods 3–5 relatively slender, moderately long. Pereopod 3 ( Figs. 3E, F View FIGURE 3 , 5C View FIGURE 5 ) overreaching distal margin of scaphocerite by length of dactylus and 0.2 of propodus; ischium with 3 spiniform setae on ventrolateral surface; merus about 14 times as long as wide, unarmed; carpus slenderer than merus, slightly shorter, unarmed, subequal in length to propodus; propodus with 3 widely spaced, minute, slender, spiniform setae on flexor margin and 2 longer spiniform seta at flexor distal margin; dactylus about 0.5 times as long as propodus, very slender (11.3 times as long as wide), simple, gently curving, with tuft of minute setae at distal 0.3 of dactylar length (near demarcation of unguis); unguis elongate, occupying 0.3 length of dactylus. Pereopod 4 ( Figs. 3G View FIGURE 3 , 5D View FIGURE 5 ) similar to pereopod 3, overreaching scaphocerite by length of dactylus; ischium with 3 spiniform setae. Pereopod 5 ( Figs. 3H View FIGURE 3 , 5E View FIGURE 5 ) distinctly longer than pereopods 3 and 4 (in particular, length of carpus-propodus combined 1.3 times of that of pereopods 3 and 4); propodus with grooming apparatus consisting of setal brush on distal half of flexor margin and 2 slender spiniform seta on flexor distal margin; dactylus similar to those of pereopods 3 and 4, 0.4 times as long as propodus.

Pleopod 2 ( Fig. 2F View FIGURE 2 ) with appendix masculina elongate, distinctly longer than appendix interna, almost reaching distal margin of endopod, with some short setae distally; appendix interna curved mesially.

Uropod ( Fig. 2G View FIGURE 2 ) with lateral lobe of protopod terminating in minute spine. Endopod and exopod narrowly ovoid, former slightly shorter than latter. Exopod with straight lateral margin terminating posteriorly in minute blunt spine, latter reaching slightly beyond base of small distolateral spiniform seta; diaeresis sinuous, without noticeable tooth mesial to distolateral spiniform seta.

Gill-exopod formula typical for genus, consisting of 1 arthrobranch above base of maxilliped 3 (well developed, multi-lamellate; Fig. 5A View FIGURE 5 ), 1 pleurobranch on each thoracomeres 4–8 (pereopods 1–5), epipods on maxilliped 1 through pereopod 4 (those on maxilliped 3 to pereopod 4 strap-like with terminal hook), flagellum-like exopod on maxilliped 1–3 and setobranch on each pereopod 1–5, corresponding to epipod on maxilliped 3 and pereopod 1–4.

Paratypes. Two paratype specimens, including one ovigerous and one non-ovigerous specimens, are generally similar to holotype. Major cheliped clearly in process of regeneration in ovigerous specimen and missing in nonovigerous specimen. Rostrum reaching or overreaching distal margin of article 2 of antennular peduncle. Minor cheliped ischium armed with either 1 or 2 spiniform setae. Pereopods 3 and 4 ischia each armed with 3 spiniform setae.

Colour in life. Not recorded.

Etymology. The Latin adjective singularis refers to the uniqueness of the new species within Salmoneus , more precisely in possessing a pair of postorbital spines on the carapace (see below).

Type locality. Uchipanari Islet, Iriomote Island, Yaeyama Islands, southern Ryukyu Islands, Japan; lower intertidal.

Distribution. Presently known only from the type locality in the Ryukyu Islands, Japan.

Habitat. Extracted from soft sediments on a seagrass bed, suggesting an infaunal life style.

Remarks. The possession of a pair of postorbital spines on the carapace is clearly the most diagnostic feature of Salmoneus singularis n. sp., separating it from all other species in the genus. Considering the combination of all remaining morphological features, the new species shows substantial affinity to several species referred to the S. gracilipes Miya, 1972 species group, i.e., S. alpheophilus Anker & Marin, 2006 , S. cavicolus Felder & Manning, 1986 , S. colinorum De Grave, 2004 , S. falcidactylus Anker & Marin, 2006 , S. gracilipes , S. pusillus Anker & Marin, 2006 , S. rashedi Ashrafi, Ďuriš & Naderloo, 2020 and S. tafaongae Banner & Banner, 1966 (cf. Anker & Marin 2006; Ashrafi et al. 2020; De Grave et al. 2020). Shared characters are the relatively long, slender rostrum, with a small subdistal spine on the ventral margin; the dorsally partly concealed eyes (with only the anterior portion of the córneas being visible in dorsal view); the slender dactyli of the pereopods 3–5; and the strongly asymmetrical chelipeds, with the major cheliped fingers armed with a row of teeth over the entire length of the occlusal margins ( Anker & Marin 2006).

The presence of postorbital spines on the carapace makes the generic placement of the present new species somewhat problematic. The presence of these spines would seem to suggest a possible relationship of S. singularis n. sp. with some members of Triacanthoneus , such as T. akumalensis Alvarez, Iliffe, Gonzalez & Villalobos, 2012 , T. alacranes Anker, 2010b , T. blanca Anker, 2020a , T. pacificus Anker, 2010b and T. toro Anker, 2010b . However, the position of these spines is somewhat different between S. singularis n. sp. and the afore-mentioned species of Triacanthoneus . In five species of Triacanthoneus , they are in “hepatic” or “post-hepatic” position ( Anker 2010b, 2020a), although they are located slightly more dorsally to the hepatic spines of other carideans, e.g., crangonids and palaemonids (cf. Holthuis 1993). In addition, the carapacial spines are in general better developed and more posteriorly located in Triacanthoneus than in S. singularis n. sp. The most parsimonious hypothesis may be that the dorsolateral spines are homologous between the new species and the five species of Triacanthoneus , but it is not easy to fully assess the homology without phylogenetic analysis.

The new species differs from all members of Triacanthoneus in the lack of a mid-dorsal spine on the carapace, which is one of the main diagnostic characters of Triacanthoneus , although its position is somewhat variable among the species ( Anker 2010b, 2020a; Alvarez et al. 2012, 2014). Other similarities between S. singularis n. sp. and Triacanthoneus are the presence of a subdistal spine on the ventral margin of the rostrum and the flexed ischio-meral articulation of the pereopods 3–5 ( Anker 2020a). These features, however, are also present in some other species of Salmoneus (e.g., Anker & Marin 2006; Komai et al. 2015). On the other side, in the general shape of the major cheliped, especially the cup-shaped, non-elongate carpus, S. singularis n. sp. is closer to almost all other species currently placed in Salmoneus , except for the cavernicolous S. sketi Fransen, 1991 and S. antricola Komai, Yamada & Yunokawa, 2015 , in which the carpus is vase-shaped or long and cylindrical, as in Triacanthoneus ( Fransen 1991; Komai et al. 2015). It is important to note here that the development of the notch on the posterior margin of the telson is variable within both genera ( Anker 2010b, 2020a; Alvarez et al. 2012, 2014); however, most species of Triacanthoneus do not have one, whereas most species of Salmoneus present a fairly deep notch, as is the case of S. singularis n. sp. ( Fig. 2C View FIGURE 2 ). Based on the presently available evidence, it seems most reasonable to assign the present new species to Salmoneus and not Triacanthoneus as rediagnosed by Anker (2020a).

Salmoneus singularis n. sp. represents the eighth species of Salmoneus to be recorded from Japanese waters, the other seven species being S. antricola , S. babai Miyake & Miya, 1966 , S. brucei Komai, 2009 , S. gracilipes , S. pinguis Komai & Anker, 2012 , S. serratidigitus ( Coutière, 1896) and S. tricristatus Banner, 1959 ( Miya 1972; Hayashi 1995; Komai 2009; Komai & Anker 2012; Komai et al. 2015). All species have been recorded from the subtropical Ryukyu Islands, with only S. gracilipes also occurring in warm temperate areas of the Japanese mainland ( Miya 1972; Anker et al. 2020). In addition, Yoshigou (2009) recorded an unidentified species similar to S. colinorum , but its identity remains to be determined.