Tethylembos japonicus Ariyama, 2004

Ariyama, Hiroyuki & Kodama, Masafumi, 2024, Three species of the family Aoridae Stebbing, 1899 (Crustacea: Amphipoda) collected from remote islands in southern Japan, with a key to all Japanese species of the family, Zootaxa 5433 (4), pp. 500-528 : 517-524

Tethylembos japonicus Ariyama, 2004

[Japanese name: Nippon-maeashi-yokoebi]

( Figs 14–18 )

Tethylembos japonicus Ariyama, 2004a: 9 , figs 6–10.

Material examined. Male, 5.1 mm (OMNH-Ar-12907), and 2 ovigerous females, 6.6, 6.0 mm (OMNH-Ar-12908, 12909), Miyanohama, Chichijima Island , Ogasawara Islands , Tokyo Prefecture, 27°06 ’ 14 ’’ N, 142°11 ’ 40 ’’ E ( Fig. 1F ), snorkeling, 2–3 m depth, among a brown alga Dictyopteris undulata , 19 July 2022, coll. M. Kodama.

Material for comparison ( Ariyama 2004a). Holotype: male, 4.5 mm (OMNH-Ar-4933), eastern part of Shionomisaki in Kushimoto , Wakayama Prefecture (33°27 ’ N, 135°48 ’ E), subtidal zone of rocky coast, phytal, 30 July 1989, coll. H. Ariyama. Allotype: ovigerous female, 6.9 mm (OMNH-Ar-4934), Kushimoto , Wakayama Prefecture, from surface of a brown alga Eckloniopsis radicosa , 29 July 1989, coll. H. Ariyama. Paratypes: male, 5.9 mm (OMNH-Ar-4935), and female, 4.9 mm (OMNH-Ar-4936), Engetsu Island in Shirahama , Wakayama Prefecture, attaching to an experimental block, 3 July 1998, coll. H. Kitada; 2 males , 4.0, 4.7 mm (OMNH-Ar-4937, 4938), and ovigerous female, 5.5 mm (OMNH-Ar-4939), Oura in Hidaka , Wakayama Prefecture, from surface of an oyster Crassostrea nippona (2 m depth), 9 August 1998, coll. H. Ariyama ; female, 4.2 mm (OMNH-Ar-4940), Kii-yura , Wakayama Prefecture, among a red alga Gelidium elegans , 6 March 1988, coll. H. Ariyama.

Type locality. Shionomisaki , Kushimoto in Wakayama Prefecture, Japan ( Ariyama 2004a) .

Description of male. Based on male, 5.1 mm (OMNH-Ar-12907).

Head ( Figs 14 , 15 ). Rostrum small, anteroventral corner slightly projected. Eyes relatively small, about quarter of head length. Antenna 1 slender; length ratio of peduncular articles 1–3 1:1.2:0.35, article 1 with 2 ventral robust setae; accessory flagellum short, with 4 long and 1 short articles; primary flagellum with 15 articles, last article minute, articles 2–14 each with aesthetasc distally. Antenna 2 shorter and thicker than antenna 1; peduncle long, length ratio of peduncular articles 3–5 1:3.3:3.55; flagellum short, shorter than peduncular article 5, consisting of 6 normal and 1 minute articles, articles 1–6 with 4, 4 (1 lost), 2, 2, 2, 2 robust setae, respectively. Upper lip produced ventrally, with many thin setae. Mandibles with length ratio of palp articles 1–3 1:1.7:2.35, article 1 bare, article 2 with 5–6 setae, article 3 almost straight, slightly narrowed distally, ventral margin with dense short setae and many long setae, medial and lateral surfaces setose dorsally; body with 5-toothed incisor, 4-toothed lacinia mobilis, 7 accessory setae and 2 plumose setae in left, and with 6-toothed incisor, 4-toothed lacinia mobilis, 7 slender accessory setae and 3 plumose setae in right; molar large, developed, surface with oblique lamellae in left. Lower lip, outer lobes with relatively long mandibular lobes, setose mediodistally, ventral surface with many thin setae, apical and ventral parts of inner lobes covered with thin setae. Maxilla 1, inner plate short and rounded, bearing a long plumose seta; outer plate with 10 distal robust setae; palp article 1 bearing a long seta, article 2 with 6 apical robust setae and 5 slender setae. Maxilla 2, inner plate narrower than outer plate; inner plate with mediodistal setae and mediofacial row of setae; outer plate bearing mediodistal long setae and laterodistal thin setae. Maxilliped, basis without triangular flange; inner plate with 3 stout robust setae distally and 1 inward robust seta; outer plate bearing 15 long-to-short robust setae mediodistally; palp article 2 long, slightly exceeding outer plate, setose medially, article 3 setose distally, article 4 narrow, with slender nail on tip.

Pereon ( Fig. 16 ). Ventral surface lacking sternal processes. Gnathopod 1 enlarged, subchelate; coxa, anteroventral corner roundly projected; basis wide, with hollow for receiving carpus anterolaterally, distal end of anterolateral margin strongly expanded anterodistally, posterior margin and medial surface each with a long seta; ischium short; merus posterior margin weakly setose; carpus roundish triangular, posterior margin setose; propodus enlarged, about 1.6 times of carpus length, posterior margin with roundish-quadrate and triangular projections distally, moderately setose, medial surface heavily setose anteriorly and weakly setose posteriorly; dactylus relatively short, almost straight, posterior margin minutely serrate. Gnathopod 2 smaller than gnathopod 1, subchelate; coxa roundish quadrate; basis slender, slightly curved anteriorly, anterodistal corner weakly expanded, anterior margin lined with several short setae, posterior margin bearing a long seta; merus posterodistal margin setose; carpus longish triangular, posterior margin setose, medial surface bearing several setae distally; propodus almost same length as carpus, palm slightly oblique, defined by a robust seta, anteromedial surface and anterodistal corner with many long setae, posterior margin moderately setose; dactylus short, curved posteriorly, posterior margin minutely serrate. Pereopods 3 and 4 similar in shape, pereopod 3 almost same length as gnathopod 2 and longer than pereopod 4; coxae roundish square; bases slender, posterior margins with a long seta; meri, carpi and propodi relatively narrow, weakly setose posteriorly; dactyli short, slightly curved posteriorly. Pereopod 5 shorter than pereopod 4; coxa bilobed; basis ovoid, with anterolateral ridge, posteroproximal corner projected, anterior margin with 2 robust setae, posterior margin bearing several short setae; merus posterodistal corner slightly projected, with a thick seta; carpus posterior margin with a robust seta, posterodistal corner bearing 1 thick and 1 robust setae; propodus with 1+1+1+2 posterior robust setae; dactylus short, curved. Pereopod 6 about 1.4 times as long as pereopod 5; coxa short, bilobed, anterior margin with 3 plumose setae; basis roundish rectangular, with anterolateral ridge, posteroproximal corner acutely projected, anterior margin with 2 robust setae, posterior margin with 1 robust and 2 plumose setae; merus posterior margin without robust setae; carpus posterior margin with 1+2 robust setae; propodus with 1+1+2+2 anterior robust setae, posterodistal corner with many long setae; dactylus short, curved. Pereopod 7 very long, about 1.4 times as long as pereopod 6; coxa short, rectangular, not lobed; basis long, almost rectangular, with anterolateral ridge, posteroproximal corner weakly projected, anterior margin with 2 small robust setae, posterior margin bearing 3 small robust setae; merus posterior margin with 2 robust setae; carpus anterior and posterior margins lacking robust setae; propodus long, anterior margin with 1+2 robust setae, posterodistal corner with dense long setae; dactylus short, curved.

Pleon ( Fig. 17 ). Epimeral plates 1–3, posteroventral corners each with small notch and minute seta, lateral surfaces with ridge, ventral margins bare. Pleopods, pleopod 2 longest; each peduncle bearing several plumose setae and 2 coupling hooks; outer rami shorter than inner rami, outer rami with 9, 9, 8 articles, respectively, inner rami with 9 articles. Uropod 1, peduncle with a basofacial robust seta, dorsal surface bearing 2 lateral and 3 medial robust setae, mediodistal corner acutely projected, ventrodistal end with long inter-ramal process (about 0.6 times length of peduncle proper); both rami longer than peduncle (about 1.1 times), outer ramus subequal in length to inner ramus, former with 2 dorsolateral, 2 dorsomedial and 4 terminal robust setae, latter bearing 3 dorsomedial and 5 terminal robust setae. Uropod 2 about 0.75 times as long as uropod 1; peduncle with long inter-ramal process at ventrodistal end (about 0.8 times length of peduncle proper), dorsal surface with 1 lateral and 1 medial robust setae distally; outer ramus about 1.2 times length of peduncle, outer ramus shorter than inner ramus, former with 2 dorsolateral, 1 dorsomedial and 4 terminal robust setae, latter bearing 2 dorsolateral, 3 dorsomedial and 5 terminal robust setae. Uropod 3 short, about half length of uropod 2; peduncle slightly longer than wide, swollen medially, ventrodistal end with short inter-ramal process, medioproximal corner with 2 short setae, distal margin bearing ventrolateral, dorsal and dorsomedial robust setae; outer ramus about 1.35 times length of peduncle, with 3 dorsolateral setae, tip bearing tiny second article and 6 long and 1 short terminal setae; inner ramus longer than outer ramus, with 2 lateral and 2 medial robust setae, tip bearing 1 robust and 3 slender setae. Telson fleshy, wider than long, with a pair of hooked cusps dorsodistally, dorsal surface with pairs of 3–4 setae and 2 short sensory setae.

Description of female. Based on ovigerous female, 6.6 mm (OMNH-Ar-12908). Almost similar to male, 5.1 mm (OMNH-Ar-12907) except for gnathopods and oostegites. Gnathopod 1 ( Fig. 17F 1-G1 ) subchelate, smaller than that of male; coxa rhomboidal; basis slightly stout, with hollow for receiving carpus anterolaterally, distal end of anterolateral margin angularly expanded anterodistally, posterior margin and medial surfaces each with a long seta; ischium short, posterodistal corner setose; merus posterior margin with many setae; carpus longish triangular, posterior margin and posteromedial surface setose; propodus long, about 1.25 times as long as carpus, posterior margin with small triangular projection bearing a robust seta, posterior margin and anterodistal corner moderately setose, medial surface with many long setae anteriorly; dactylus long, curved, posterior margin minutely serrate. Gnathopod 2 ( Fig. 17F 1-G 2 ) smaller than gnathopod 1, subchelate; coxa wide, roundish; basis straight, anterodistal corner faintly expanded, anterior margin with several short setae, posterior margin bearing 2 long setae; merus posterodistal margin setose; carpus longish triangular, anterior margin with a few setae, posterior margin densely setose; propodus almost same length as carpus, palm weakly oblique, smooth, defined by a robust seta, anterior and posterior margins moderately setose, anteromedial surface bearing several setae; dactylus short, curved posteriorly, posterior margin minutely serrate.

Coloration in life. Male, 5.1 mm (OMNH-Ar-12907, Fig. 18A ): head faintly-brownish white with light brown patches, eyes dark brown and white; pereonites and pleonites also faintly-brownish white with light brown patches; antenna 1 light brown and partly white, antenna 2 faintly-brownish white and partly light brown; gnathopods, pereopods, pleopods and uropods faintly-brownish white. Ovigerous female, 6.0 mm (OMNH-Ar-12909, Fig. 18B ): almost same as male, but deeper; eggs green.

Remarks. Morphological features of the specimens from the Ogasawara Islands well agree with the original description of Tethylembos japonicus ( Ariyama 2004a) except for the shape of the gnathopod 1 basis in both sexes. The original T. japonicus has the anterolateral margin of the basis almost straight, whereas the margin is strongly expanded anterodistally in the Ogasawara specimens. Re-examination of the type specimens revealed that “almost straight” should be corrected to “strongly expanded anterodistally” (see Fig. 17 M-G1-DB and F2-G1-DB); therefore, the Ogasawara specimens can be identified as T. japonicus .

Habitat. Among algae and surfaces of block and oyster in the shallow subtidal zone (2–3 m depth).

Distribution. Japan: from Kushimoto to Kii-yura in Wakayama Prefecture ( Ariyama 2004a), and the Ogasawara Islands in Tokyo Prefecture (present study).

Figures

FIGURE 1. Map showing collecting sites of the examined specimens.

FIGURE 2. Protolembos ryukyuensis sp. nov. Holotype, male, 8.8 mm (OMNH-Ar-12888). Habitus.

FIGURE 14. Tethylembos japonicus Ariyama, 2004. Male, 5.1 mm (OMNH-Ar-12907). Habitus.

FIGURE 15. Tethylembos japonicus Ariyama, 2004. Male, 5.1 mm (OMNH-Ar-12907). Scales: 0.05 mm.

FIGURE 16. Tethylembos japonicus Ariyama, 2004. Male, 5.1 mm (OMNH-Ar-12907). Scales: 0.1 mm.

FIGURE 17. Tethylembos japonicus Ariyama, 2004. All except for M, F1 and F2: male, 5.1 mm (OMNH-Ar-12907); M, holotype, male, 4.5 mm (OMNH-Ar-4933); F1, ovigerous female, 6.6 mm (OMNH-Ar-12908); F2, allotype, ovigerous female, 6.9 mm (OMNH-Ar-4934). Scales: 0.1 mm.

FIGURE 18. Tethylembos japonicus Ariyama, 2004. Photograph of live specimens by M. Hirose.A: male, 5.1 mm (OMNH-Ar- 12907); B: ovigerous female, 6.0 mm (OMNH-Ar-12909).