Nikoides subdistalis, Komai & Hirabayashi, 2021

Komai, Tomoyuki & Hirabayashi, Isao, 2021, A new species of the processid shrimp genus Nikoides Paul’son, 1875 (Decapoda: Caridea) from Japan, Zootaxa 5057 (1), pp. 114-126 : 116-124

publication ID	https://doi.org/ 10.11646/zootaxa.5057.1.7
publication LSID	lsid:zoobank.org:pub:CFF38AB9-FE38-491E-9219-0A1BE0D7EAFC
DOI	https://doi.org/10.5281/zenodo.5587951
persistent identifier	https://treatment.plazi.org/id/D8349FD3-FA5A-43F5-A93B-B2E2AC37B848
taxon LSID	lsid:zoobank.org:act:D8349FD3-FA5A-43F5-A93B-B2E2AC37B848
treatment provided by	Plazi
scientific name	Nikoides subdistalis
status	sp. nov.

Treatment

Nikoides subdistalis n. sp.

[New Japanese name: Togetsuno-minami-rousoku-ebi]

( Figs. 1–6 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6 )

Material examined. All specimens were collected from Sabiura, Arita , Kushimoto , Wakayama Prefecture (Kii Peninsula) by the second author (IH) using SCUBA equipment. Holotype: CBM-ZC 16573, ovigerous female (cl 9.1 mm), 12 m deep, 26 May 2019.

Paratypes. CBM-ZC 16574, 1 ovigerous female (cl 9.1 mm), 12 m deep, 8 July 2018, DNA voucher; CBM-ZC 16575, 1 male (cl 8.0 mm), 12.3 m, 23 June 2021; CBM-ZC 16576, 1 male (cl 7.7 mm), 7.3 m deep, 25 June 2021; CBM-ZC 16577, 1 female (cl 10.7 mm), 7 m deep, 14 July 2021.

Diagnosis. Rostrum slightly overreaching anteriorly extended eyes, dorsal tooth relatively large, subdistal in position (located at distal 0.2 of rostral length), ventral margin concave. Pleomere 5 with pleuron faintly angular or rounded. Pleomere 6 with posterolateral lobe terminating in spine. Telson with 2 pairs of dorsolateral spines, posterior margin drawn out into spiniform projection. Antennular peduncle with stylocerite distinctly bi-toothed. Antennal scaphocerite with distolateral spine overreaching blade, basicerite bearing 1 blunt process on ventral face in addition to distolateral spine. Pereopod 2 distinctly unequal with right longer than left; right with 52–62 carpal segments, left with 25–28 carpal segments. Pereopods 3 and 4 ischia each with 2 spiniform setae; propodus of pereopod 4 with 2 rows of tufts of short stiff setae on extensor surface in male, only with sparse setae in female; pereopod 5 propodus with 2 rows of tufts of short setae on extensor surface in both male and female. Maximum postorbital carapace length 10.7 mm.

Description. Holotype ovigerous female. Body ( Figs. 1A View FIGURE 1 ; 2A, B View FIGURE 2 ) moderately robust for genus.

Rostrum ( Fig. 3A, B View FIGURE 3 ) slender, 0.3 times as long as carapace, widened at base in dorsal view, nearly straight, directed forward, slightly overreaching distal corneal margins; apex simple, acuminate; dorsal margin armed with 1 small tooth located at distal 0.25 and with tuft of short setae just anterior to base of tooth; lateral face ventrally with submarginal row of short setae extending onto orbital margin; ventral margin nearly straight. Carapace ( Figs. 2A View FIGURE 2 ; 3A, B View FIGURE 3 ) dorsal midline rounded, dorsal outline in lateral view nearly straight; orbital margin evenly concave; suborbital lobe well developed, separated from antennal spine by deep concavity; antennal spine distinct; anterolateral margin below antennal spine shallowly concave, pterygostomial angle rounded, with fringe of short setae.

Thoracic sternite 7 ( Fig. 3C View FIGURE 3 ) with low transverse crest divided into 2 parts by shallow median notch. Sternite 8 ( Fig. 3C View FIGURE 3 ) with semicircular plate divided by two parts by deep, slit-like median cleft followed by deep groove.

Pleon( Figs. 2B View FIGURE 2 ; 3D View FIGURE 3 ) smooth, almost glabrous, ventral margins of pleura1–5 rounded ventrally or posteroventrally. Pleomere 6 1.3 times as long as pleomere 5, 1.2 times as long as high, with acute posteroventral tooth; posterolateral process acuminate. Sternites 1–5 unarmed.

Telson ( Figs. 2B View FIGURE 2 ; 3E, F View FIGURE 3 ) about twice length of pleomere 6, gradually tapering; dorsal surface medially grooved in anterior half, bearing transverse row of short setae near base and 2 pairs of dorsolateral spiniform setae, these setae subequal in length; anterior spiniform setae located at 0.25 of telson length, posterior pair at 0.6 of telson length; posterior margin drawn into median spine, flanked by 2 pairs of unequal spiniform setae (mesial pair exceeding twice length of lateral pair, distinctly overreaching posteromedial spine).

Eye ( Figs. 2A View FIGURE 2 ; 3B View FIGURE 3 ) large, slightly depressed dorsoventrally, corneal width subequal to length of eyestalk and cornea combined, 0.25 of carapace length.

Antennular peduncle ( Figs. 2A View FIGURE 2 ; 3B View FIGURE 3 ) overreaching rostral apex by 0.4 length of article 1 and falling short of distal margin of antennal scaphocerite. Ultimate article about half-length of penultimate article. Penultimate article about 4.7 times as long as basal width. Basal article longer than distal two articles combined, with ventral tooth located slightly distal to midlength; stylocerite ( Fig. 3B, G View FIGURE 3 ) bi-toothed distally, mesial tooth larger than lateral tooth, directed distomesially, lateral tooth directed distolaterally. Outer flagellum with thickened proximal portion consisting of 25 articles (distal 10 articles bearing aesthetascs); inner flagellum long, at least twice as long as carapace.

Antennal peduncle ( Figs. 2A View FIGURE 2 ; 3A, B View FIGURE 3 ) with scaphocerite 0.8 times as long as carapace, 5 times as long as wide; distolateral spine slightly overreaching rounded distal margin of blade. Basicerite with small ventrolateral distal spine; ventral surface with small tubercle-like projection bearing apical seta. Carpocerite reaching midlength of scaphocerite.

Mouthparts not dissected.

Maxilliped 3 ( Fig. 4A View FIGURE 4 ) moderately slender, overreaching antennal scaphocerite by length of ultimate article. Antepenultimate article subequal in length to distal two articles combined; proximal 0.3 of dorsal margin shallowly excavated. Penultimate article (= carpus) subcylindrical. Ultimate article subequal in length to penultimate article, gradually tapering to spine-like apex; mesial surface with grooming apparatus consisting of several transverse or obliquely transverse tracts of stiff setae and some spiniform setae adjacent to dorsal margin. Exopod not reaching midlength of antepenultimate article.

Left pereopod 1 ( Fig. 4B, C View FIGURE 4 ) non-chelate, slightly longer and slenderer than right, reaching distal margin of antennal scale by tip of dactylus; ischium short; merus slightly shorter than propodus and carpus combined, with sparse row of setae on dorsal and ventral margins; carpus distinctly shorter than propodus; propodus tapering distally, 4.9 times as long as greatest width, with sparse row of tufts of individual setae on extensor and flexor margins; dactylus gently curved, 0.3 times as long as propodus; exopod well developed, reaching proximal 0.2 of merus. Right pereopod 1 ( Fig. 4D, E View FIGURE 4 ) chelate, moderately slender, reaching distal margin of antennal scale by tip of chela; ischium short; merus not tapering distally and proximally, distinctly longer than chela and carpus combined, dorsal and ventral margins with row of setae; carpus cup-shaped, subequal in length to palm; chela 4.8 times as long as wide, fingers 0.6 length of palm, noticeably curved distally and crossing each other; exopod reaching midlength of merus.

Pereopods 2 ( Fig. 4F, G View FIGURE 4 ) strongly asymmetrical, right appreciably longer than left. Left pereopod 2 ( Fig. 4F View FIGURE 4 ) overreaching distal end of basicerite by mero-carpal articulation, overreaching distal margin of scaphocerite by 0.7 length of carpus; ischium not subdivided, subequal in length to merus, with distinct proximal lobe on ventral margin; merus divided into 9 segments; carpus divided into 26 segments; chela with dactylus about 0.7 times as long as palm. Right pereopod 2 ( Fig. 4G View FIGURE 4 ) long, reaching distal end of scaphocerite by mero-carpal articulation; ischium slightly shorter than merus, with 3 faint annulation distally, ventral margin with distinct proximal lobe; merus divided into 21 segments; carpus divided into 52 segments; dactylus subequal in length to palm.

Pereopod 3 ( Fig. 5A, B View FIGURE 5 ) moderately long and slender, overreaching scaphocerite by 0.3 length of carpus, combined lengths of propodus and carpus slightly longer than that of merus and ischium; ischium with 2 widely spaced spiniform setae on lateral face ventrally, ventral margin with row of short setae; merus with 5 evenly spaced spiniform setae on lateral face, ventral margin with row of setae; carpus elongate, 1.8 times as long as propodus, with sparse setae on extensor and flexor margins; propodus also with tufts or individual short setae on extensor and flexor margins; dactylus slightly curved, simple, 0.2 times as long as propodus, with subapical tuft of short setae on lateral face. Pereopod 4 ( Fig. 5C, D View FIGURE 5 ) distinctly longer than pereopod 3, overreaching scaphocerite by 0.3 length of carpus, combined lengths of propodus and carpus distinctly longer than that of merus and ischium; ischium with 2 widely spaced, slender spiniform setae on lateral face ventrally, ventral margin with row of short setae; merus with 4 spiniform setae on lateral face, ventral margin with row of short setae; carpus elongate, 1.7 times as long as propodus, with sparse setae on extensor and flexor margins; propodus also with sparse tufts or individual setae on extensor and flexor margins; dactylus 0.2 times as long as propodus, gently curved, with subapical tufts of short setae on lateral face. Pereopod 5 ( Fig. 5E–G View FIGURE 5 ) shorter than pereopods 3 and 4, overreaching antennal scale by 0.2 length of propodus; ischium unarmed on lateral face, ventral margin with sparse setae; merus 1.5 times as long as ischium, unarmed, with row of sparse setae on ventral margin; carpus 0.8 times as long as propodus, with row of sparse setae on extensor margin, with few setae on flexor margin; propodus with row of about 20 tufts of short setae on extensor surface laterally and sparse row of longer individual setae mesially, flexor margin with 6 evenly spaced, slender spiniform setae and tufts of thin setae, flexor distal margin with pair of spiniform setae; dactylus gently curved, 0.2 times as long as propodus, with subdistal tuft of short setae on lateral face.

Pleopods 1–5 ( Fig. 2B View FIGURE 2 ) normal, without distinctive features.

Uropod ( Figs. 2B View FIGURE 2 ; 3H View FIGURE 3 ) with protopod subacutely pointed posterolateral angle. Endopod elongate subovate, reaching beyond tip of telson, with scattered short setae on dorsal surface. Exopod slightly longer and distinctly wider than endopod; lateral margin faintly sinuous, terminating posteriorly in small spine; diaeresis distinct, notched laterally, armed with spiniform setae just mesial to posterolateral spine.

Paratypes. Generally similar to holotype. Carapace dorsal outline in lateral view nearly straight or slightly sinuous. Antennular upper flagellum with thickened proximal portion relatively longer in male than in female ( Fig. 6A View FIGURE 6 ); aesthetascs better developed in male than in female. Left pereopod 2 with 6–12 meral and 25–29 carpal segments; right pereopod 2 with 20–27 meral and 57–62 carpal segments. Pereopod 3 propodus with or without 2 rows of tufts of short stiff setae in male ( Fig. 6B View FIGURE 6 ), always without setal rows in female. Pereopod 4 propodus with 2 rows of about 20 tufts of short stiff setae in male ( Fig. 6C View FIGURE 6 ), without such setal rows in female. Pereopod 5 propodus with 25–30 tufts of short stiff setae in both male ( Fig. 6D View FIGURE 6 ) and female, Male pleopod 1 endopod ( Fig. 6E View FIGURE 6 ) with nearly straight mesial and noticeably convex lateral margins, former with row of slender, stiff setae; appendix interna well differentiated, stout, terminal in position, with cluster of adhesive hooks on mesial side; distolateral lobe triangular, far exceeded by appendix interna. Male pleopod 2 ( Fig. 6F, G View FIGURE 6 ) with appendix masculina elongate, rod-like, reaching distal 0.3 of endopod, bearing some bristle-like setae apically.

Size. Largest male cl 8.0 mm; largest female cl 10.7 mm, ovigerous females (two specimens available) cl 9.1 mm.

Colouration in life. Fig. 1A View FIGURE 1 . Body and appendages generally pinkish semi-translucent, body with scattered white spots; cornea gray. Eggs in non-eyed stage greenish gray.

Distribution. Presently known only from Kushimoto, Kii Peninsula (Wakayama Prefecture), Japan; at depths of 7– 12 m.

Ecological note. Nocturnal life style of processid shrimp has been well documented (e.g., Hayashi 1991a; Unsworth et al. 2007; De Grave & Anker 2013). The present new species is no exception. The type specimens of Nikoides subdistalis n. sp. were all collected at night from sandy bottom mixed with dead coral rubble or reef head, where they were roaming ( Fig. 1B View FIGURE 1 ). In aquarium, specimens were observed to burrow into sand or rubble during daytime, and to be active at night.

Etymology. The specific epithet refers to the subdistal position of the dorsal tooth on the rostrum in the new species.

Remarks. Nikoides subdistalis n. sp. is readily distinguished from the 10 known congeners by the characteristic armature of the rostrum. In the new species, the dorsal rostral tooth is relatively large and located at the distal 0.25 of the rostrum, being fairly remote from the rostral apex ( Figs. 3A View FIGURE 3 ; 6A View FIGURE 6 ). Nikoides maldivensis also has a distinct dorsal tooth on the rostrum, but the tooth is located at about the midlength of the rostrum and is still larger in the new species (cf. Hayashi 1975: fig. 5a). In other nine species, the rostrum is bifid at the apex, or with the dorsal tooth is located at the subapical position ( Hayashi 1975; Hayashi 1981; Noël 1986; Burukovsky 2002, 2007). Nikoides maldivensis resembles N. subdistalis n. sp. also in the deeply bi-toothed antennular stylocerite, but the shape of the stylocerite is substantially different between the two species. In the new species, both distal teeth are acute, the distomesial tooth is distinctly stronger than the distolateral tooth. In contrast, in N. maldivensis , the distomesial tooth is blunt; the distolateral tooth is slender and acuminate, distinctly exceeding the distomesial tooth.

In the genetic analysis using the mitochondrial 16S rRNA gene, a DNA matrix of 444 aligned base positions of four taxa ( N. danae , N. schmitti , N. subdistalis n. sp. and Nikoides sp. ) was obtained (a complete deletion option was employed). The interspecific divergence among the four taxa ranges from 17.9–23.5% ( Table 3 View TABLE 3 ), well supporting that these four taxa are specifically distinct.

From Japanese waters, the following six species of Nikoides have been recorded ( Hayashi 1975, 1981; 1991a, 1991b; Minemizu 2014): N. danae , N. gurneyi , N. maldivensis , N. multispinatus , N. sibogae and N. steini .All species occur in the Ryukyu Islands, but only N. sibogae has been recorded from the Japanese mainland, i.e., Kii Strait and Tosa Bay ( Hayashi 1975; Baba et al.1986). The present new species is the seventh of the Japanese representative of the genus and the second of the genus occurring in the Japanese mainland.