Salmoneus aduncus Komai 2022, n. sp.
Creators: name: Komai, Tomoyuki
Publisher: name: Zenodo
Year: 2022
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Alpheidae
Salmoneus
Salmoneus aduncus

description: Salmoneus aduncus n. sp.
[New Japanese name: Kagitsume-nokogiri-teppou-ebi]
(Figs. 1–5)
Material examined. Holotype: CBM-ZC 17107, non-ovigerous specimen (cl 6.3 mm), TRV “Toyoshio-maru”, 2009-21 cruise, stn 8, W of Yashiro Island, Iyo-nada, Seto Inland Sea, Japan, 33°54.92′N, 132°09.12′E, 17–25 m, 29 October 2009, dredge, coll. K. Kakui.
Paratype. CBM-ZC 7305, non-ovigerous specimen (cl 4.6 mm), TRV “Toyoshio-maru”, 1997-05 cruise, stn 2, E of Hashira-jima Island, Seto Inland Sea, 34°00’N, 137°27’E, 36 m, 27 May 1997, dredge, coll. T. Komai.
Description. Holotype. Body (Fig. 1) moderately slender.
Rostrum (Fig. 2A, B) narrowly triangular with straight lateral margins in dorsal view, 0.2 times as long as carapace, 1.6 times as long as basal width, curved slightly downward, flattened dorsoventrally, reaching distal margin of basal article of antennular peduncle; dorsal surface with trace of median carina; ventral surface carinate medially, with minute blunt tooth subterminally; tip acuminate in dorsal view; bluntly angular in lateral view. Carapace (Figs. 1, 2A, B) almost glabrous on surface, with prominent, subconical tubercle at about 0.4 length; dorsal profile in lateral view almost straight; orbital spine small, directed anteriorly; anterolateral margin sinuous, pterygostomial angle broadly rounded; cardiac notch moderately deep.
Pleon (Fig. 1) with anterior 3 pleura rounded marginally; pleuron 4 with tiny posteroventral tooth; pleuron 5 also with tiny posteroventral tooth. Pleomere 6 1.4 times as long as high, without articulated posteroventral plate, with faint suture visible inside; preanal plate rounded; posterolateral process short, terminating in acute tooth. Telson (Fig. 2C) relatively wide, tapering distally, 2.3 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 0.75 of telson length; posterior margin damaged at right side, intact left side bearing 2 long, unequal spiniform setae (mesial somewhat longer and stouter than lateral) and 1 minute seta mesially.
Cornea (Fig. 2A, B) subglobular, partially exposed in dorsal view, fully exposed in lateral view; no anteromesial spinule or tubercle apparent.
Antennular peduncle (Fig. 2A, B) stout, overreaching distal margin of antennal scaphocerite by 0.7 length of distal article. Basal article with small, anteriorly directed tooth on ventromesial ridge; stylocerite tapering to slightly overreaching distal margin of basal article, its dorsal surface somewhat inflated. Intermediate article subquadrate, about twice as long as wide. Lateral flagellum (Fig. 2A) biramous, with fused portion very short; secondary ramus composed of 4 units with several groups of aesthetascs.
Antenna (Fig. 2A, B, E) peduncle basicerite bearing ventrolateral distal spine; dorsodistal margin not particularly produced. Scaphocerite 0.4 times as long as carapace, subovate with faintly convex lateral margin and gently convex mesial margin; distal blade broadly rounded, reaching slightly beyond moderately small distolateral spine. Carpocerite short, stout, falling slightly short of distal margin of scaphocerite. Flagellum stout, somewhat flattened.
Epistomial sclerites each with low protuberance. Upper lip with crested median lobe.
Mouthparts typical for genus in external observation (not illustrated).
Maxilliped 3 (Fig. 3A, B) moderately slender, overreaching distal margin of antennal scaphocerite by halflength of ultimate article. Coxa with semi-circular lateral plate. Antepenultimate article slightly sinuous, proximal half flattened dorsoventrally. Penultimate article (= carpus) slightly widened distally. Ultimate article 1.9 times as long as and wider than penultimate article, tapering distally from mid-length to acute tip obscured by subterminal setae; mesial face with several transverse tracts of stiff serrulate setae.
Pereopods 1 (= cheliped) strongly asymmetrical in shape and unequal in size. Major (left) cheliped (Fig. 4A–D) carried flexed, overreaching distal margin of scaphocerite by length of chela and carpus, when extended. Ischiummerus somewhat compressed, slender, slightly flexed at articulation in lateral view, gently sinuous in ventral view; ischium about 0.6 times as long as merus, nearly straight in lateral view, slightly arched in ventral view; merus straight in lateral view, gently arched in ventral view, narrowing in proximal half. Carpus very short, subrectangular in outline, with 2 low protuberances on lateral surface. Chela subequal in length to carapace, slightly twisted; palm subcylindrical, 1.7 times as long as wide, with shallow longitudinal depressions on lateral surface dorsally and ventrally, lateral margin slightly convex, mesial margin with faint notch at base of pollex; pollex and dactylus strongly compressed; pollex gently curved, terminating in acute tip, occlusal margin with row of 4 small blunt teeth in proximal 0.3, otherwise unarmed; dactylus much broader than pollex, 1.2 times as long as palm, widened to distal 0.2 length, distal part abruptly tapering to acute tip and strongly curved, occlusal margin with row of 5 blunt teeth in proximal 0.3, otherwise unarmed.
Minor (right) cheliped (Fig. 3C, D) about half-length of major cheliped. Ischium-merus linear, merus 1.3 times as long as ischium. Carpus-chela combined subequal in length to ischium-merus combined; carpus slightly widened distally. Chela 0.7 times as long as carpus; occlusal margins of pollex and dactylus unarmed; dactylus gently curved, 1.4 times as long as palm.
Pereopod 2 (Fig. 3E) reaching distal margin of antennal scaphocerite. Merus 1.3 times as long as ischium. Carpuschela combined subequal in length to ischium-merus combined. Carpus consisting of 5 segments, proximalmost segment longest, distinctly longer than distal 4 segments combined. Chela small, 0.3 times as long as carpus; dactylus 1.5 times as long as palm.
Pereopods 3–5 moderately slender. Pereopod 3 (Fig. 3F, G) overreaching distal margin of antennal scaphocerite by half-length of propodus; ischium slightly widened distally, with 3 spiniform seta on lateral face; merus slightly narrowing distally, 5.8 times as long as greatest width, unarmed; carpus 1.1 times as long as propodus, unarmed; propodus with few minute setae at flexor distal margin and 1 minute spiniform seta at midlength of flexor margin; dactylus slender, gently curved, gradually tapering to acute tip, approximately half-length of propodus. Pereopod 4 (Fig. 3H, I) overreaching distal margin of scaphocerite by length of dactylus, generally similar to pereopod 3 in general armature and article proportions, but slightly slenderer; ischium with 2 spiniform setae on lateral face; dactylus 0.6 times as long as propodus. Pereopod 5 (Fig. 3J, K) ischium-merus shorter than those of pereopods 3 and 4, but carpus-propodus-dactylus distinctly longer than those of pereopods 3 and 4; ischium unarmed; merus 2.4 times as long as ischium, 7 times as long as wide; carpus 0.9 times as long as propodus; propodus with grooming apparatus on flexor margin distally, consisting of 5 transverse rows of serrulate setae; dactylus about 0.4 times as long as propodus.
Pleopod 1 (Fig. 2F, G) endopod about half-length of exopod, tapering to blunt terminus. Pleopod 2 (Fig. 2H) appendix masculina 1.5 times as long as appendix interna, with several setae on distal 0.3 of lower margin.
Uropod (Fig. 2I) protopod with posterolateral angle terminating in acute tooth; posteromedial lobe also terminating in acute tooth. Exopod ovate, with small acute posterolateral tooth and well-developed posterolateral spiniform seta; diaeresis sinuous. Endopod as long as exopod, narrowly ovoid, without specific features.
Paratype. Generally similar to holotype. Major cheliped and both pereopods 3 missing. Rostrum unarmed ventrally. Telson with 2 pairs of unequal spiniform setae and 1 mesial pair of stiff setae on posterior margin (Fig. 2D).
Colouration in fresh. Body, antennular and antennal peduncles, and uropods entirely orange; antennular and antennal flagella, maxilliped 3 and pereopods 1–5 all white; pleopods 1–5 pale orange (Fig. 5).
Distribution and habitat. Presently known only from the Seto Inland Sea, Japan, at depths of 17– 36 m. The two specimens are both collected from sand bottom. No evidence for association with other organisms has been obtained due to sampling deficiencies. The closely related Salmoneus rostratus is known to live in burrows of gobyassociated burrowing Alpheus shrimps (cf. Anker 2003; Anker & Marin 2006).
Etymology. From the Latin word aduncus (= hooked), in reference to the strongly hooked dactylus of the major cheliped of the new species.
Remarks. The present new species is strikingly similar to Salmoneus rostratus in the morphological aspect. The latter species has been recorded widely from the tropical Indo-West Pacific (Barnard 1962; De Grave & Wilkins 1997; Anker 2003; Anker & Marin 2006; Sha et al. 2019), but Anker & Marin (2006) noticed minor differences among specimens from different localities. Shared characters between S. aduncus n. sp. and S. rostratus include: the carapace has a distinct gastric tubercle; the dactylus of the major cheliped is broad, abruptly tapering to a strongly hooked distal part; occlusal teeth on the pollex and dactylus of the major cheliped are restricted to the proximal half or less. Only two specimens are available for the new species for study, and consequently evaluation of intraspecific variation is not easy. Nevertheless, the following minor particulars may be useful in differentiating morphologically the new species from S. rostratus: (1) the telson is relatively wider in S. aduncus n. sp. than in S. rostratus (Fig. 2C versus Anker & Marin 2006: fig. 14j); (2) longitudinal grooves on the major cheliped palm are less pronounced in S. aduncus n. sp. than in S. rostratus (cf. Fig. 4A, C, D) versus Barnard 1962: fig. 1c; Anker 2003: fig. 3c; Anker & Marin 2006: figs. 14 d, e, 15c, d); (3) occlusal teeth on the major cheliped pollex and dactylus are weaker in S. aduncus n. sp. than in S. rostratus (cf. Fig. 4C, D versus De Grave & Wilkins 1997: fig. 1e; Anker 2003: fig. 3c; Anker & Marin 2006: figs. 14e, 15d). The living colouration may be different between the new species and S. rostratus: in the new species, the body is generally orange (Fig. 5), whereas in S. rostratus, it is entirely vivid maroon red (Anker & Marin 2006: fig. 7b, c).
Salmoneus aduncus n. sp. is also similar to S. bruni Banner & Banner, 1966, originally described from the Gulf of Thailand, in the general shape and armature of the major cheliped, but it is distinguished from the latter by the presence of a gastric tubercle on the carapace (Figs. 1, 2A) and the ischium of the pereopod 3 being armed with three spiniform setae (Fig. 3F). In S. bruni, there is no gastric tubercle on the carapace; the ischium of the pereopod 3 is unarmed (Banner & Banner 1966: fig. 11a, b, i).
The topology of the best ML tree (Fig. 6) shows that S. aduncus n. sp. and S. rostratus are in sister relation with 82% bootstrap support. The K2P genetic divergence between S. aduncus n. sp. and S. rostratus is 3.3%, which falls within the range of interspecific K2P genetic divergence within Salmoneus (1.6 to 13.9%; Table 2). The recognition of the new species is supported also by the genetic evidence.
In the Japanese mainland, only S. gracilipes has been recorded from Honshu and Kyushu (Miya 1972; Hayashi 1995; Anker et al. 2020), although other seven species have been recorded from the Ryukyu Islands. The new species is the second of Salmoneus to be recorded from the Japanese mainland, although its real distribution remains to be clarified.
description: Published as part of Komai, Tomoyuki, 2022, A new species of the alpheid shrimp genus Salmoneus Holthuis, 1955 (Decapoda: Caridea) from the Seto Inland Sea, Japan, pp. 436-448 in Zootaxa 5200 (2) on pages 438-446, DOI: 10.11646/zootaxa.5200.5.2, http://zenodo.org/record/7270847