Thuylamea shiranui, Komai, 2018

Komai, Tomoyuki, 2018, A new species of the alpheid shrimp genus Thuylamea Nguyên, 2001 (Crustacea: Decapoda: Caridea) from Yatsushiro Sea, Kyushu, Japan, Zootaxa 4378 (3), pp. 387-396 : 388-395

publication ID	https://doi.org/ 10.11646/zootaxa.4378.3.7
publication LSID	lsid:zoobank.org:pub:110496AC-8F8B-473F-A633-4EC0E4081838
DOI	https://doi.org/10.5281/zenodo.5975385
persistent identifier	https://treatment.plazi.org/id/D6ACA18B-A941-4A23-AA18-123E67306F8A
taxon LSID	lsid:zoobank.org:act:D6ACA18B-A941-4A23-AA18-123E67306F8A
treatment provided by	Plazi
scientific name	Thuylamea shiranui
status	sp. nov.

Treatment

Thuylamea shiranui View in CoL n. sp.

[New Japanese name: Shiranui-teppou-ebi] Figs 1–6 View FIGURE 1 View FIGURE 2 View FIGURE3 View FIGURE 4 View FIGURE 5 View FIGURE 6

Material examined. Holotype: CBM-ZC 14145, female (cl 5.1 mm; pereopods 2 and 4 missing), NE of Gosho-ura Island , 32°21.458'N, 130°22.906′E, 29 m, silt, stn 17, Smith-McIntyre grab, 30 May 2017. GoogleMaps

Paratype: CBM-ZC 14146, 1 specimen, sex not determinable (cl 3.7 mm; heavily damaged, antennae missing, only left maxilliped 3, left pereopod 1, 2 and 5 preserved), same data as holotype; CBM-ZC 14147, 1 female (cl 4.7 mm; antennae and maxillipeds 3 missing, only pereopods 1 present) GoogleMaps , same data as holotype; CBM-ZC 14 148, 1 female (cl 6.7 mm; maxilliped 3 damaged; all pereopods except for right pereopod 1 missing), off Hondo, Amakusa, 32°23.337′N, 130°13.647′E, 28.7 m, stn 14, Smith-McIntyre grab, silt and sand, 30 May 2017 GoogleMaps ; CBM-ZC 14149, 1 male (cl 4.3 mm; all pereopods missing), E of Himedo, Kami-Amakusa, 32°25.704’N, 130°27.712’E, 27 m, stn 13, Smith-McIntyre grab, silt, 31 May 2017.

Description of female holotype. Body ( Fig. 1A, B View FIGURE 1 ) elongate, subcylindrical; integument glabrous.

Rostrum ( Fig. 2A, B View FIGURE 2 ) very short, broadly triangular, flattened dorsoventrally, directed slightly downward; tip sharply pointed; lateral margin merging into evenly concave orbital margin; ventral surface unarmed. Carapace ( Figs 1A View FIGURE 1 , 2A View FIGURE 2 ) with broadly rounded anterolateral margin, without armature; length about twice of height; dorsum generally rounded in anterior half, dorsal profile in lateral view nearly straight, having shallow median sulcus between gastric and cardiac regions; posterodorsal margin slightly elevated in broad transverse ridge; cardiac notch deep.

Pleon ( Fig. 1B View FIGURE 1 ) with anterior 3 pleura rounded ventrally or posteroventrally; pleura 4 and 5 produced posteriorly but rounded, unarmed. Pleomere 6 1.3 times as long as pleomere 5, 1.3 times as long as high, without articulated plate at posteroventral angle; dorsal surface with short transverse groove anteriorly; posteroventral angle blunt; preanal plate unarmed; posterolateral process rounded. Telson ( Fig. 2C View FIGURE 2 ) 1.1 times as long as pleomere 6 and 2.3 times as long as wide, slightly narrowing posterior to mid-length, with 2 pairs of small dorsolateral spiniform setae (anterior pair located at about mid-length of telson, posterior pair at 0.6 length of telson); posterior margin produced, rounded, with row of long setae flanked by 2 lateral pairs of minute spiniform setae; dorsal surface nearly flat.

Eyestalks ( Figs 1A View FIGURE 1 , 2B View FIGURE 2 ); supplemented by Fig. 2H View FIGURE 2 of paratype) short, stout, subtriangular with produced anteromesial angles, contiguous, covered with frontal margin of carapace in dorsal view, cornea partially visible in lateral view, small, rounded, darkly pigmented, with scattered whitish spots possibly representing reduced facets.

Antennular peduncle ( Figs 1A View FIGURE 1 , 2B View FIGURE 2 ) about 0.4 times as long as carapace, exceeding distal margin of scaphocerite by half-length of article 2, but not reaching end of antennal carpocerite. Article 1 about twice as long as wide, gently inflated proximally with well-developed statocyst lobe; ventromesial ridge with strong subdistal spine directed forward; stylocerite closely adjoining lateral side of article 1, gradually tapering to spine falling slightly short of distal margin of article 1. Article 2 somewhat depressed, subequal in length to article 1, 3.0 times as long as wide. Article 3 short, also somewhat depressed, less than half length of article 2. Outer flagellum subequal in length to peduncle, bifurcate at eighth or ninth article; shorter ramus consisting of 2 or 3 articles, bearing some aesthetascs; longer ramus slender, multiarticulate; mesial flagellum much slenderer and slightly shorter than lateral flagellum.

Antenna ( Figs 1A View FIGURE 1 , 2B, D View FIGURE 2 ) with basicerite stout, with small, acute ventrolateral distal tooth. Distomesial angle of article 3 strongly produced distally. Carpocerite elongate (about 5 times as long as wide), subcylindrical, exceeding far beyond distal margin of scaphocerite by 0.3 of its length. Scaphocerite short, about 0.3 times as long as carapace, 2.5 times as long as wide, elongate subovate; lateral margin nearly straight, terminating in small spine falling slightly short of broadly rounded distal lamella.

Epistome ( Fig. 2F View FIGURE 2 ) with laminar median tooth.

Mouthparts not dissected, similar to those of T. camelus in external observation (cf. Nguyen 2001: figs 7–11).

Maxilliped 3 endopod ( Figs 1A View FIGURE 1 , 5A View FIGURE 5 ) moderately slender, reaching as far as distolateral spine of antennal scaphocerite. Coxa with lateral plate triangular with forwardly directed apex, bearing strap-like epipod arising from ventral surface ( Fig. 5B View FIGURE 5 ). Antepenultimate article sinuously curved in dorsal view, proximal half flattened dorsoventrally. Penultimate article (= carpus) subcylindrical, slightly widened distally. Ultimate article 1.4 times as long as penultimate article, gradually tapering distally, terminating in blunt tip, bearing some short terminal setae; mesial face with several transverse tracts of stiff serrulate setae. Exopod flagellum-like, overreaching distal end of antepenultimate article.

Pereopods 1 (chelipeds) ( Figs 3 View FIGURE3 , 4 View FIGURE 4 ) enlarged, subequal in length, symmetrical between right and left, extended forward, with dactylus articulated laterally to palm. Ischium short, strongly compressed, unarmed. Merus more strongly compressed proximally; dorsal margin sinuous; ventral margin nearly straight. Carpus short, cup-shaped, about half-length of merus. Chela subequal in length to carapace. Palm subcylindrical, slightly compressed dorsoventrally, 4.1 times (left) or 4.3 times (right) as long as wide, generally smooth on surfaces; ventral surface with shallow, saddle-like transverse depression proximal to base of fingers; dactylar articulation armed with triangular tooth on either side (left chela; Fig. 3E, F View FIGURE3 ) or unarmed (right chela; Fig. 4C, D View FIGURE 4 ); adhesive plaque poorly developed. Fixed finger slender, tapering to slightly curved unguis; ventral surface with shallow concavity proximally; occlusal margin proximally with low, rounded tooth, otherwise without conspicuous armature. Dactylus broad, strongly flattened, laminar, not tapering distally, slightly twisted, about 0.7 times as long as palm and about 3.7 times as long as wide; occlusal margin slightly serrulate with 1 low, broadly rounded proximal tooth, ending in a small spiniform claw exceeded by broadly rounded dactylar terminal margin; outer and trminal margins sharply edged, with row of short setae becoming more numerous distally.

Only left pereopod 3 and right pereopod 5 preserved. Pereopod 3 ( Fig. 5C View FIGURE 5 ) moderately stout; ischium widened distally, unarmed; merus strongly compressed laterally, narrowing distally; carpus slightly widened distally, distinctly shorter than merus, bearing extensor distal process; propodus subequal in length to carpus; dactylus ( Fig. 5D View FIGURE 5 ) slender, 0.8 times as long as propodus, slightly compressed dorsoventrally, very slightly curved. Pereopod 5 ( Fig. 5E View FIGURE 5 ) generally similar to pereopod 3, but distinctly shorter; carpus subequal in length to merus; propodus subequal in length to carpus, bearing grooming apparatus consisting of obliquely transverse rows of stiff serrulate setae increasing in length distally; dactylus slightly twisted, 0.8 times as long as propodus.

Pleopod 1 ( Fig. 5F View FIGURE 5 ) with small endopod about 0.3 length of exopod, not tapering, with slight notch on mesial margin, terminal margin rounded; exopod subequal in length to protopod. Pleopod 2 ( Fig. 5G View FIGURE 5 ) with protopod slightly longer than rami; endopod slightly longer than exopod, with appendix interna arising at mid-length of mesial margin and distally curved mesially. Appendices internae of pleopods 3–5 similarly curved mesially.

Uropod ( Fig. 2G View FIGURE 2 ) with protopod divided into 2 lobes by deep, narrow incision, each lobe terminating in tiny spine. Endopod and exopod suboval, subequal in length, overreaching posterior tip of telson. Exopod slightly thick, setose lateral margin terminating distally in light angle, forming base of tiny distolateral spiniform seta; diaeresis transverse, unarmed.

Notes on paratypes. All paratypes are more or less damaged; pereopod 2 (left) preserved only in the smallest specimen (cl 3.7 mm, sex not determinable; CBM-ZC14146); none of the specimens with pereopod 4.

Paratypes generally similar to holotype. Carapace dorsum flattened in anterior half and rounded in posterior half in male (CBM-ZC 14149), whereas rounded entirely in smallest specimen (CBM-ZC 14146); in other two female paratypes (CBM-ZC 14147, 14148), carapace dorsum similar to that of holotype. Eyestalks as figured ( Fig. 2H View FIGURE 2 ). Antennular peduncle overreaching distal margin of antennal scale by 0.2–0.4 length of article 2; lateral antennular flagellum bifurcate at 8th article in male paratype (CBM-ZC 14149) and at 11th article in largest female paratype (CBM-ZC 14148) (in other two specimens, the antennule and antennae are missing). Cheliped palm 4.3– 4.4 times as long as wide; dactylar articulation of palm without tooth in all preserved chela ( Fig. 4C, D View FIGURE 4 ) (1 pair from CBM-ZC 14147; one side from CBM-ZC 14146 and 14148). Pereopod 2 ( Fig. 5H View FIGURE 5 ) of smallest specimen with merus subequal in length to ischium; carpus divided into 5 articles, length ratio (proximal to distal) 2.9: 0.8: 0:8: 0.6: 1; chela about half-length of carpus; dactylus 1.7 times as long as palm.

Male pleopod 1 ( Fig. 5I View FIGURE 5 ) with endopod less than half-length of exopod, proportionally narrower than female endopod, with 3 plumose setae terminally and shorter scattered simple setae on ventral surface and mesial margin; exopod slightly longer than protopod. Male pleopod 2 ( Fig. 5J View FIGURE 5 ) with protopod slightly longer than rami; endopod with appendices interna and masculina arising at mid-length of mesial margin, appendix interna straight, rod-like, appendix masculina also rod-like, distinctly longer than appendix interna, bearing 5 simple setae in distal half; exopod slightly shorter than endopod.

Colour in life. Unknown.

Etymology. Derived from another Japanese name of the type locality. “Shiranui” Sea is another name of the Yatsushiro Sea, referring to a kind of mysterious mirage occurring in the area, called as “ shiranui ”.

Distribution and habitat. So far known only from Yatsushiro Sea, western Kyushu, Japan; at depths of 27– 29 m. All specimens were collected from silt sediments using a Smith-McIntyre grab; other information on ecology is presently unavailable. Other benthic animals found in these samples were: Labiosthenolepis sp. (Polychaeta: Polynoidae ; stn 13, 14, 17), Sigambra hanaokai (Kitamori) (Polychaeta: Plargidae: stn 13, 14, 17), Magelona japonica Okunoda (Polychaeta: Magelonidae ; stn 13, 14, 17), Asthenognathus inaequipes Stimpson (Brachyura: Varunidae ; stn 13, 17), Amphiuridae sp. (Ophiuroidea; stn 13, 14, 17), Glandiceps hacksi Marion (Enteropneusta: Spengelidae ; stn 13, 17), and Paratrypauchen microcephalus (Bleeker) (Teleostei: Gobiidae ; stn 13, 14, 17).

Remarks. The type series of the new species consists of one small specimen of unidentified sex (cl 3.7 mm), three female (none ovigerous) specimens (cl 4.7–6.7 mm) and one male specimen (cl 4.3 mm). As noted above, none of them is intact. The largest female (CBM-ZC 14148, paratype, cl 6.7 mm, total length about 20 mm) has an ovary with partially formed eggs, which is visible inside the cephalothorax ( Fig. 6 View FIGURE 6 ), suggesting the sexual maturity. The type series of T. camelus consists of five male specimens (total length 31–39 mm) ( Nguyen 2001). Considering the possible variation related to size and sex, a small male specimen of T. camelus (ZRC 1994.4387, cl 4.2 mm) was examined for comparison. The description of a female specimen from Guangdong, South China, provided by Wang & Sha (2016), is also referred for the comparison.

The present new species share many features with Thuylamea camelus , e.g., the elongate, subcylindrical body; the greatly reduced rostrum; the unarmed frontal or anterolateral margins of the carapace; the absence of an articulated flap at the posteroventral angle of the pleomere 6; the partially exposed eyes, the elongate carpocerite of the antennal peduncle; and the enlarged, anteriorly extended, symmetrical chelipeds, with thin lamella-like dactyli positioned laterally. As has been described by Nguyen (2001) and Wang & Sha (2016), T. camelus is quite distinctive in having peculiar submedian crests near the posterodorsal margin of the carapace. Anker & De Grave (2016) remarked that the submedian crests on the posterior part of the carapace is poorly developed in their young male specimen from Singapore, suggesting the ontogenetic variation in the development of this peculiar structure. Reexamination of this specimen (ZRC 1994.4387) has confirmed that there is a pair of low tubercles ( Fig. 7A, B View FIGURE 7 ), corresponding to the prominent crests in the adults, near the posterodorsal margin of the carapace. As described above, the posterior part of the carapace dorsum is smooth without any ornamentation in T. shiranui n. sp. The antennular peduncle is relatively longer in T. shiranui n. sp. than in T. camelus [overreaching the distal margin of the antennal scaphocerite by the 0.2–0.5 length of the article 2 in T. shiranui n. sp. ( Fig. 1A View FIGURE 1 ) versus just reaching or overreaching it by the half-length of the article 3 in T. camelus ( Fig. 7A View FIGURE 7 )]. Furthermore, comparison with the description of a female specimen (cl 11.5 mm) given by Wang & Sha (2016) shows that the shape of the cheliped dactylus is different between the two species. In T. shiranui n. sp., the claw is exceeded by the rounded terminal margin of the dactylus ( Figs 3E View FIGURE3 , 4C, D View FIGURE 4 ), whereas in T. camelus , the unguis is terminal in the position ( Wang & Sha 2016: fig. 1F). In the small male specimen from Singapore, the claw of the cheliped dactylus is also terminal, although in the adult males, the claw is exceeded by the terminal margin of the dactylus ( Nguyên 2001: fig 13). The observation suggests that the shape of the dactylus is ontogenetically variable in males of T. camelus and is sexually dimorphic.

With the addition of the new species and the observed intraspecific variation in T. camelus , the generic diagnosis of Thuylamea (see above) is slightly emended.

Nguyên (2001) emphasized the uniqueness of Thuylamea , not specifying closely related taxa. Anker et al. (2006), who performed phylogenetic analysis of Alpheidae using morphological characters, estimated that the sister taxon of Thuylamea camelus is Notalpheus imarpe Méndez & Wicksten, 1982 , a unique member of the genus Notalpheus Méndez & Wicksten, 1982 and that the next closely related taxon is Orygmalpheus politus De Grave & Anker, 2000 , the type species of the monotypic Orygmalpheus . However, these two allied genera are morphologically quite different from Thuylamea (cf. Méndez & Wicksten 1982; De Grave & Anker 2000).