Salmoneus antricola, Komai, Tomoyuki, Yamada, Yusuke & Yunokawa, Kyo, 2015

Komai, Tomoyuki, Yamada, Yusuke & Yunokawa, Kyo, 2015, A new cave-dwelling species of the alpheid shrimp genus Salmoneus Holthuis, 1955 (Crustacea: Decapoda: Caridea) from the Ryukyu Islands, southern Japan, Zootaxa 4028 (3), pp. 413-420 : 414-419

publication ID	https://doi.org/ 10.11646/zootaxa.4028.3.6
publication LSID	lsid:zoobank.org:pub:45E8CEBA-FC8A-4359-9E65-574F1490D990
DOI	https://doi.org/10.5281/zenodo.3505808
persistent identifier	https://treatment.plazi.org/id/060187D5-FF81-6177-FF55-FF63FC60F8E4
treatment provided by	Plazi
scientific name	Salmoneus antricola
status	sp. nov.

Treatment

Salmoneus antricola View in CoL n. sp.

[New Japanese name: Gama-nokogiri-teppou-ebi] ( Figs. 1–5 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 )

Material examined. Holotype: Ohoba No. 2 Cave, Ie Island, Okinawa Islands, Ryukyu Archipelago, Japan, 12 m, 2015, scuba diving, coll. Y. Yamada and K. Yunokawa, ovigerous specimen (cl 5.7 mm), CBM-ZC 13120.

Description. Medium-sized species of Salmoneus (cl of ovigerous specimen 5.7 mm), with moderately slender body ( Fig. 1 View FIGURE 1 ). Rostrum ( Fig. 2 View FIGURE 2 A, B) reaching distal margin of second segment of antennular peduncle, dorsoventrally flattened, triangular, longer than wide at base, horizontal in lateral view, without distinct mid-dorsal carina; lateral margins faintly concave in dorsal view; tip acute, straight; ventral margin with minute subdistal tooth. Carapace ( Figs. 1 View FIGURE 1 , 2 View FIGURE 2 A, B) slightly inflated dorsally, surface glabrous; anterolateral region with faint suture; cardiac notch deep; orbital teeth small compared to rostrum, subtriangular, acute distally, directed slightly anterolaterally; anterolateral margin below orbital tooth broadly sinuous, pterygostomial angle broadly rounded.

Pleon ( Fig. 1 View FIGURE 1 ) with anterior 3 pleura rounded posteroventrally; fourth pleuron with tiny posteroventral tooth; fifth pleuron with larger posteroventral tooth. Sixth pleomere without distinct articulated plate, but with faint suture; preanal plate rounded; posterolateral process short, terminating in sharp tooth. Telson ( Fig. 2 View FIGURE 2 C) damaged (posterior part missing); dorsal surface with 2 pairs of small dorsolateral spines.

Eyes ( Fig. 2 View FIGURE 2 A, B) contiguous, partly concealed, with anterior-most portion visible in both dorsal and lateral view; anterior surface flattish; cornea located at anterolateral part of eyestalk, somewhat reduced, darkly pigmented, with several small white dots, possibly representing facets, on dorsal half ( Fig. 5 View FIGURE 5 C).

Antennular peduncle ( Fig. 2 View FIGURE 2 A, B) stout with second segment about as long as wide, slightly overreaching distal end of antennular peduncle. First segment with small, anteriorly directed tooth on ventromesial ridge; stylocerite terminating in slender, acute tooth reaching mid-length of second article, dorsal part somewhat compressed laterally, dorsal margin sharply carinate and broadly convex in lateral view. Distolateral margin of second segment with small notch. Lateral flagellum ( Fig. 2 View FIGURE 2 A) biramous, fused portion very short; accessory ramus with several long aesthetascs arranged in 2 rows.

Antenna ( Fig. 2 View FIGURE 2 A, B, D) with basicerite terminating in small tooth distoventrally, dorsomesial margin broadly bilobed distally. Scaphocerite subovate with nearly straight lateral margin and gently convex mesial margin; distal blade broadly rounded, reaching well-beyond small distolateral tooth. Carpocerite very short, stout, falling short of mid-length of scaphocerite.

Epistomial sclerites each with small anteromesial spine. Upper lip with crested median lobe.

Mouthparts typical for genus (not figured; external observation made).

Third maxilliped ( Fig. 3 View FIGURE 3 A) slender, falling short of distal margin of antennal scale. Coxa with lateral plate above strap-like epipod, rounded-subquadrate ( Fig. 3 View FIGURE 3 B). Antepenultimate segment sinuously curved, proximal half flattened dorsoventrally. Penultimate segment subcylindrical, dorsally with subterminal tuft of long stiff setae followed by row of long setae decreasing in length proximally. Ultimate segment tapering distally from mid-length, terminating in minute apical spinule, bearing 1 long subterminal seta; mesial face with several transverse tracts of stiff serrulate setae.

First pereopods (chelipeds) strongly unequal in size and asymmetrical in shape; major (left) cheliped about twice length of minor (right) cheliped, more robust; basis of each cheliped with conspicuous, subtriangular dorsal process ( Fig. 4 View FIGURE 4 A, D).

Major cheliped ( Fig. 3 View FIGURE 3 C) elongate, slender, in full extension overreaching distal margin of antennal scaphocerite by length of chela, carpus and 0.2 of merus length. Ischium slightly curved, with 3 small movable spines on ventrolateral surface. Merus about 7.5 times as long as greatest width, smooth, slightly depressed distoventrally, ventral margin slightly sinuous; ventral surface not conspicuously depressed. Carpus elongate, about 0.8 times as long as merus, distally widening, lateral surface slightly inflated distally ( Fig. 4 View FIGURE 4 B). Chela ( Fig. 4 View FIGURE 4 C) slightly compressed, suboval in cross-section, smooth, mesial surface gently convex; fingers elongate, 1.9 times as long as palm, strongly compressed laterally; finger tips strongly curved, crossing, acuminate; cutting edge of dactylus with 6 widely spaced, small, acute teeth; space between teeth slightly convex, smooth; cutting edge of pollex with 5 teeth similar to those of dactylus in distal 0.7 of pollex length, with row of at least 7 minute adjacent teeth in proximal 0.2 of pollex length.

Minor cheliped ( Fig. 3 View FIGURE 3 D) in full extension overreaching distal margin of antennal scaphocerite by length of chela. Ischium with 3 spines on ventrolateral surface. Merus slightly longer than ischium, with narrow ventral surface. Carpus slightly shorter than merus, widening distally, 4.5 times as long as distal width. Chela ( Fig. 3 View FIGURE 3 E) tapering distally, subequal in length to carpus; palm slightly depressed; fingers subequal in length to palm, not crossing distally, cutting edges unarmed, forming thin blade.

Second pereopod ( Fig. 3 View FIGURE 3 F, G) slender, moderately long. Ischium unarmed. Merus subequal in length to ischium. Carpus about 0.8 times as long as ischium and merus combined, subdivided into 5 articles, ratio of carpal articles from proximal to distal equal to: 4.7: 0.6: 0.6 1.1: 1.0. Chela slightly longer than distalmost carpal article.

Third to fifth pereopods slender, elongate. Third pereopod ( Fig. 3 View FIGURE 3 H, I) overreaching distal margin of antennal scaphocerite by full length of propodus; ischium with 1 subdistal spine on ventrolateral surface; merus about 14 times as long as wide, unarmed; carpus slenderer than merus, but subequal in length, unarmed; propodus with 5 slender movable spinules on ventral margin and 1 longer spinule at distoventral margin; dactylus about 0.3 times as long as propodus, slender (8.7 times as long as wide), simple, very slightly curving, with tuft of minute setae at distal 0.2 of dactylar length. Fourth pereopod ( Fig. 3 View FIGURE 3 J) similar to third pereopod; ischium unarmed. Fifth pereopod ( Fig. 3 View FIGURE 3 K) longer than third and fourth pereopods; ischium unarmed; carpus and propodus elongate, with welldeveloped setal brush on distal half of flexor margin.

Second pleopod with appendix masculina slightly longer than appendix interna ( Fig. 2 View FIGURE 2 E), distal half of lateral margin bearing row of 7 short setae.

Uropod ( Fig. 2 View FIGURE 2 F) with lateral lobe of protopod terminating in small subacute tooth. Endopod and exopod narrowly ovoid, former slightly shorter than latter. Exopod with straight lateral margin terminating posteriorly in small blunt process covering base of small distolateral movable spine; diaeresis sinuous, without noticeable tooth mesial to distolateral spine.

Gill-exopod formula typical for genus; third maxilliped and first through fourth pereopods bearing strap-like epipods.

Color in life. Body ( Fig. 5 View FIGURE 5 A, B) entirely yellowish translucent; ovary visible through integument as orange mass; cornea black, with white dots, possibly representing facets, on dorsal half ( Fig. 5 View FIGURE 5 C); pereopods translucent; eggs in eyed stage yellowish orange ( Fig. 5 View FIGURE 5 A).

Distribution. Presently known only from the type locality, Ohoba No. 2 Cave, Ie Island, Okinawa Islands, Japan.

Habitat. The holotype of Salmoneus antricola n. sp. was collected in a marine cave (named “Ohoba No. 2”) at a depth of 12 m, about 20 m from the entrance. Shrimp was on course sand bottom; the environment of the collection site was of aphotic; the water temperature at the time of the collection was about 25°C. Some individuals of the same species were encountered in the cave ( Fig. 5 View FIGURE 5 B), but not collected.

Remarks. Salmoneus antricola n. sp. has clear morphological similarities with S. erasimorum Dworschak, Anker & Abed-Navandi, 2000 , S. komaii Anker, 2011a , S. paulayi Anker, 2011a , S. poupini Anker, 2011a , and S. sketi Fransen, 1991 , all assigned to the fairly heterogeneous S. jarli ( Holthuis, 1951) species group ( Anker & Marin 2006; Anker 2011a), characterized mainly by the possession of small, widely spaced teeth on the cutting edges of the slender fingers of the major cheliped ( Fransen 1991; Anker 2011a). However, the combination of the elongate carpus of the minor cheliped (subequal in the length to the chela), the lack of teeth on the cutting edges of the minor cheliped fingers, the elongate second pereopod with the length of the first carpal article being subequal to that of the merus, and the very slender third to fifth pereopods, immediately distinguishes the new species from the five above-listed species. In these, the carpus of the minor cheliped is cup-like, distinctly shorter than the palm; the minor cheliped fingers bear a row of teeth on their cutting edges; the second pereopod is less elongate and with the first carpal article distinctly shorter than the merus; and the third to fifth pereopods are moderately slender, not quite as slender as in the new species ( Fransen 1991; Dworschak et al. 2001; Anker 2011a). Furthermore, in S. antricola n. sp., the basis of the first and second pereopods bears a peculiar subtriangular process on the proximodorsal portion; such a process has not been mentioned or illustrated in previous descriptions of species of Salmoneus and thus may be autapomorphic of the new species. The rostrum of S. antricola n. sp. is relatively longer and narrower than that of the first four species, but shorter than that of S. sketi , in which it may reach the distal end of the third article of the antennular peduncle. The glabrous carapace and the weakly inflated palm of the major cheliped separate S. antricola n. sp. from S. komaii , S. paulayi and S. poupini , in which the carapace bears scattered short setae at least on the dorsal surface, whereas the major cheliped palm is more strongly inflated, somewhat bulbous. In addition, S. paulayi and S. poupini have a unique configuration on the finger cutting edges of the major chela, consisting of thin, broadly rounded and finely striated plates, intercalated between strong teeth ( Anker 2011a); these plates not being present in S. antricola n. sp. The ischium of the second pereopod is armed with one or two spines in S. erasimorum , S. komaii , S. poupini and S. sketi , in contrast to the unarmed ischium of S. antricola n. sp. and S. paulayi . Among the five species presumably closely related to S. antricola n. sp., only S. sketi inhabits marine caves ( Fransen 1991).

Salmoneus jarli is the most distinctive species of the S. jarli species group because of the absence of teeth on the cutting edges of the unusually short major cheliped fingers, and also on the cutting edges of the minor cheliped fingers ( Holthuis 1951; Anker 2010). Anker (2010) suggested that S. jarli may be more distantly related to the other species referred to the S. jarli species group. The fact that the present new species lacks teeth on the fingers of the minor cheliped, may place S. antricola n. sp. between S. jarli and the other species of the S. jarli species group, although the absence of teeth on the minor cheliped is a common feature in several other groups of Salmoneus .

The discovery of S. antricola n. sp. brings the total number of the species of Salmoneus known from Japan to seven, the other six species being S. babai Miyake & Miya, 1966 , S. brucei Komai, 2009 , S. gracilipes Miya, 1972 , S. pinguis Komai & Anker, 2012 , S. serratidigitus ( Coutière, 1897) and S. tricristatus Banner, 1959 ( Hayashi 1995; Komai 2009; Komai & Anker 2012). The identity of S. serratidigitus requires reassessment ( Anker 2003). Considering the recent discoveries of numerous new species of Salmoneus in the Indo-West Pacific, there is no doubt that more species are awaiting to be discovered in Japanese waters.

Etymology. The specific epithet is a combination of the Latin “ antrum ” (= cave) and “- cola ” (dweller), in reference to the habitat of the new species; used as a noun in apposition.