Protolembos ryukyuensis, Ariyama & Kodama, 2024

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 : 504-509

Protolembos ryukyuensis sp. nov.

[Japanese name: Ryūkyū-maeashi-yokoebi, new]

( Figs 2–7 )

Type material. Holotype: male, 8.8 mm (OMNH-Ar-12888), Yaeyama Laboratory of the Japan Fisheries Research and Education Agency ( Fukai-ōta , Ishigaki Island , Okinawa Prefecture), 24°27 ’ 17 ’’ N, 124°12 ’ 49 ’’ E ( Fig. 1B ), rearing tank, 17 December 2021, coll. T. Sanda . Paratypes: 2 males, 7.4, 7.2 mm (OMNH-Ar-12889, 12890), ovigerous female, 8.0 mm (OMNH-Ar-12891), and female with juveniles, 7.9 mm (OMNH-Ar-12892), same data as holotype; male, 7.6 mm (OMNH-Ar-12893), Arakawa, Ishigaki Island , Okinawa Prefecture, 24°21 ’ 31 ’’ N, 124°07 ’ 16 ’’ E ( Fig. 1C ), intertidal, among a seagrass Cymodocea rotundata , 18 May 2022, coll. H.Yamada & I. Tanita ; ovigerous female, 7.4 mm (OMNH-Ar-12894), Arakawa, Ishigaki Island , Okinawa Prefecture, 24°21 ’ 21 ’’ N, 124°07 ’ 26 ’’ E ( Fig. 1D ), intertidal, among a seagrass Cymodocea rotundata , 19 May 2022, coll. H. Yamada & I. Tanita ; 3 males, 8.4, 8.4, 8.3 mm (OMNH-Ar-12895–12897), 2 females, 7.9, 7.9 mm (OMNH-Ar-12898, 12899), and ovigerous female, 7.4 mm (OMNH-Ar-12900), Kubota, Tanegashima Island , Kagoshima Prefecture, 30°49 ’ 32 ’’ N, 131°03 ’ 44 ’’ E ( Fig. 1A ), using SCUBA, 2–3 m depth, among a brown alga Sargassum alternato-pinnatum , 23 June 2022, coll. M. Kodama.

Type locality. Fukai-ōta , Ishigaki Island in Okinawa Prefecture, Japan .

Etymology. Referring to the collected sites. Both of Ishigaki Island and Tanegashima Island belong to the Ryukyu Archipelago.

Description of male. Based on holotype, male, 8.8 mm (OMNH-Ar-12888) and paratype, male, 7.4 mm (OMNH-Ar-12889) only for epimeral plates.

Head ( Figs 2 , 3 ). Rostrum small, anteroventral corner acutely projected. Eyes relatively small, about quarter length of head. Antenna 1 slender; length ratio of peduncular articles 1–3 1:1.5:0.35, article 1 with 2 ventral robust setae; accessory flagellum long, with 7 long and 1 minute articles; primary flagellum with 26+ articles, tip lost. Antenna 2 shorter and thicker than antenna 1; peduncle long, length ratio of peduncular articles 3–5 1:4.0:4.45; flagellum short, shorter than peduncular article 5, consisting of 13 normal and 1 minute articles, articles 2–13 each with 2 robust setae. Upper lip produced ventrally, bearing many thin setae. Mandibles with length ratio of palp articles 1–3 1:1.3:2.45, article 1 bare, article 2 with 3–4 short setae, article 3 almost straight, narrowed distally, ventral margin with dense short setae and many long setae, medial surface setose dorsally, dorsolateral surface with several setae; body with 5-toothed incisor, 4-toothed lacinia mobilis and 8 serrated accessory setae in left, and with 5-toothed incisor, 5-toothed lacinia mobilis, 7 serrated accessory setae and 2 plumose setae in right; molar large, developed, surface with rounded plate in left. Lower lip, outer lobes with relatively long mandibular lobes (lost in right), setose mediodistally, ventral surface with many thin setae, apical 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 8 apical robust setae and 4 slender setae. Maxilla 2, both plates subequal in shape; inner plate with distal and medial setae and mediofacial row of setae; outer plate bearing distal long setae and laterodistal thin setae. Maxilliped, basis with triangular flange on laterodistal corner; 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 4 narrow, with slender nail on tip.

Pereon ( Fig. 4 ). Ventral surface lacking sternal processes. Gnathopod 1 greatly enlarged, subchelate; coxa rhomboidal; basis stout, with hollow for receiving carpus and propodus anterolaterally, distal end of anterolateral margin weakly expanded distally, posterior margin with a long seta; ischium short; merus posterior margin with many plumose setae; carpus triangular, posterior margin bearing many plumose setae; propodus greatly enlarged, about 4.1 times length of carpus, posterior margin with quadrate and longish-triangular projections distally, heavily setose with plumose setae, anterodistal corner bearing a few simple setae; dactylus long, slightly curved, posterior margin minutely serrate. Gnathopod 2 smaller than gnathopod 1, subchelate; coxa roundish; basis slender, slightly curved anteriorly, anterior margin with many plumose setae, posterior margin bearing 3 long setae; merus posterodistal margin with many plumose setae; carpus long, narrow, anterior margin densely setose with plumose setae, posterior margin bearing many plumose setae; propodus also narrow, about 0.9 times as long as carpus, palm strongly oblique, defined by a robust seta, anterior and posterior margins with dense and many plumose setae, respectively, but anterodistal corner bearing several simple setae; dactylus short, curved posteriorly, posterior margin minutely serrate. Pereopods 3 and 4 similar in shape, pereopod 3 slightly longer than pereopod 4, almost same length as gnathopod 2; coxae roundish square; bases slender, posterior margins with 5–6 long setae; meri, carpi and propodi relatively narrow, weakly setose posteriorly; dactyli short, curved posteriorly. Pereopod 5 slightly longer than pereopod 4; coxa bilobed, anteromedial surface setose; basis rectangular, with anterolateral ridge, posteroproximal corner projected, anterior margin with 7 short robust setae, posterior margin bearing 2 plumose setae; merus with a robust seta at posterodistal corner; carpus and propodus with 1+2+3 and 1+1+1+2 posterior robust setae, respectively; dactylus short. Pereopod 6 about 1.35 times as long as pereopod 5; coxa short, bilobed, anterior margin with several plumose setae; basis rectangular, with anterolateral ridge, posteroproximal corner projected, anterior margin with 6 small robust setae, posterior margin with 2 small robust setae and 4 plumose setae; merus posterior margin and posterodistal corner each with a robust seta; carpus anterior and posterior margins with 1 and 1+2+1+2 robust setae, respectively; propodus with 1+1+1+2+1+2+2 anterior robust setae, posterodistal corner with many long setae; dactylus short, curved. Pereopod 7 very long, about 1.45 times as long as pereopod 6; coxa short, ovoid, not lobed, anterior margin with 3 plumose setae; basis long rectangular, with anterolateral ridge, posteroproximal corner projected, anterior margin with 5 small robust setae, posterior margin with 5 small robust setae and 4 plumose setae; merus posterior margin with 5 robust setae; carpus anterior and posterior margins with 3 and 5 robust setae, respectively, anterodistal corner bearing 2 robust setae medially; propodus anterior margin with 8 single and 1 double robust setae, posterodistal corner with dense long setae; dactylus short, curved.

Pleon ( Fig. 5 ). 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 many plumose setae and 2 coupling hooks; outer rami shorter than inner rami, former with 15–16 articles, latter with 16 articles. Uropod 1, peduncle with a basofacial robust seta, dorsal surface bearing 3 lateral and 7 medial robust setae, mediodistal corner triangularly projected, ventrodistal end with long inter-ramal process (about 0.45 times length of peduncle proper); both rami longer than peduncle, outer ramus subequal in length to inner ramus, former with 2 dorsolateral, 4 dorsomedial and 4 terminal robust setae, latter bearing 1 ventrolateral, 1 dorsolateral, 6 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 0.6 times length of peduncle proper), dorsal surface with 2 lateral and 3 (1 lost) medial robust setae; outer ramus about 1.3 times length of peduncle, outer ramus shorter than inner ramus, former with 4 dorsolateral, 5 dorsomedial and 4 (1 lost) terminal robust setae, latter bearing 3 dorsolateral, 6 dorsomedial and 5 terminal robust setae. Uropod 3 about 0.65 times length of uropod 2; peduncle slightly longer than wide, swollen medially, ventrodistal end with short inter-ramal process, medial margin with 1 slender and 1 short robust setae, distal margin bearing dorsolateral, dorsomedial and ventrolateral robust setae; outer ramus about 1.9 times length of peduncle, with several lateral setae and 3 medial robust setae, tip bearing tiny second article and 5 long and 2 short terminal setae; inner ramus longer than outer ramus, with 3 lateral and 5 medial robust setae, tip bearing 1 robust and 3 short slender setae. Telson fleshy, slightly wider than long, with a pair of hooked cusps dorsodistally, dorsal surface with pairs of 2 setae and 2 short sensory setae.

Description of female. Based on paratype, female with juveniles, 7.9 mm (OMNH-Ar-12892). Almost similar to holotype, male, 8.8 mm (OMNH-Ar-12888) except for gnathopods and oostegites. Gnathopod 1 ( Fig.5 F-G1) subchelate, smaller than that of male; coxa rhomboidal; basis stout, with hollow for receiving carpus anterolaterally, distal end of anterolateral margin weakly expanded anterodistally, posterior margin with a small robust seta, medial surface bearing 3 long setae and 2 robust setae; ischium short, posterodistal corner setose; merus posterior margin setose; carpus triangular, posterodistal corner with many setae; propodus long, about 1.75 times as long as carpus, posterior margin with indistinct projection and triangular projection bearing a small robust seta, posterior margin weakly setose; dactylus long, curved, posterior margin minutely serrate. Gnathopod 2 ( Fig. 5 F-G2) smaller than gnathopod 1, subchelate; coxa wide, roundish, posteroproximal margin with 4 thick setae; basis straight, anterodistal corner pointed, anterior margin with several short setae, posterior margin bearing 2 (1 lost) long setae; merus posterodistal margin densely setose; carpus longish triangular, anterior margin with several setae, posterior margin densely setose; propodus slightly shorter than carpus (about 0.95 times), palm weakly oblique, smooth, defined by a robust seta, anterior and posterior margins weakly and strongly setose, respectively; dactylus short, curved posteriorly, posterior margin minutely serrate.

Variation ( Fig. 6 ). Paratype, male, 8.3 mm (OMNH-Ar-12896): gnathopod 1 ( Fig. 6G 1 ), propodus posterodistal margin with angular and acute teeth; gnathopod 2 ( Fig. 6G 2 ), carpus and propodus narrower than those of holotype, male, 8.8 mm (OMNH-Ar-12888); pereopods 3 and 4 ( Fig. 6P 3 , P 4 ), meri and carpi wider than those of holotype; pereopod 5 ( Fig. 6P 5 ), basis without posterior plumose setae. Paratype, male, 8.3 mm (OMNH-Ar-12897): gnathopod 1 ( Fig. 6M 1-G1 ), propodus posterior margin with a robust seta proximal to triangular projection. Paratype, male, 8.4 mm (OMNH-Ar-12895): gnathopod 1 ( Fig. 6M 2-G 1 ), propodus posterior margin with minute proximal projection and a short robust seta. Paratype, ovigerous female, 7.4 mm (OMNH-Ar-12894): gnathopod 1 ( Fig. 6F 1-G1 ), propodus posterior margin with indistinct and triangular projections and a long robust seta. Paratype, ovigerous female, 8.0 mm (OMNH-Ar-12891): gnathopod 1 ( Fig. 6F 2-G 1 ), propodus posterior margin with 2 indistinct projections and 2 long robust setae (probably abnormal because of abnormal denticles on dactylus posterior margin).

Coloration of frozen-thawed specimens. Holotype, male, 8.8 mm (OMNH-Ar-12888, Fig. 7A ): head yellowish brown with dark brown patches, eyes light brown; pereonites and pleonites dark yellow with dark brown bands or patches; antenna 1 peduncular articles 1, 2 and antenna 2 peduncular articles 4, 5 crimson, other parts of antennae pale crimson and white; gnathopods and pereopods faintly-brownish white; pleopods and uropods pale brown. Paratype, ovigerous female, 8.0 mm (OMNH-Ar-12891, Fig. 7B ): head yellowish brown with brown speckles, eyes light brown; pereonites and pleonites yellowish brown with light brown bands or patches; antenna 1 peduncular article 1 light brown, other parts of antenna 1 and antenna 2 faintly-brownish white; gnathopods, pereopods, pleopods and uropods faintly-brownish white.

Remarks. Morphological features of this new species indicate that this species belongs to the genus Protolembos (see Table 1 ). Protolembos ryukyuensis sp. nov. is characterized by the posteriorly setose male gnathopod 1 and the anteriorly setose male gnathopod 2. This new species shares both features with four congeners ( P. arinyas , P. clematis , P. murrarum , and P. yaranus ); however, all these species have the heavily setose basis and ischium of the male gnathopod 1, whereas those of P. ryukyuensis are slightly setose.

Natural habitat. Among seagrass and algae in the intertidal zone and the shallow subtidal zone (2–3 m depth).

Distribution. Japan: Ishigaki Island in Okinawa Prefecture and Tanegashima Island in Kagoshima 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 3. Protolembos ryukyuensis sp. nov. Holotype, male, 8.8 mm (OMNH-Ar-12888). Scales: 0.1 mm.

FIGURE 4. Protolembos ryukyuensis sp. nov. Holotype, male, 8.8 mm (OMNH-Ar-12888). Scales: 0.3 mm.

FIGURE 5. Protolembos ryukyuensis sp. nov. All except for M and F: holotype, male, 8.8 mm (OMNH-Ar-12888); M: paratype, male, 7.4 mm (OMNH-Ar-12889); F: paratype, female with juveniles, 7.9 mm (OMNH-Ar-12892). Scales: 0.2 mm.

FIGURE 6. Protolembos ryukyuensis sp. nov. All except for M1, M2, F1 and F2: paratype, male, 8.3 mm (OMNH-Ar-12896); M1: paratype, male, 8.3 mm (OMNH-Ar-12897); M2: paratype, male, 8.4 mm (OMNH-Ar-12895); F1: paratype, ovigerous female, 7.4 mm (OMNH-Ar-12894); F2: paratype, ovigerous female, 8.0 mm (OMNH-Ar-12891). Scales: 0.2 mm.

FIGURE 7. Protolembos ryukyuensis sp. nov. Photograph of frozen-thawed specimens by M. Kodama. A: holotype, male, 8.8 mm (OMNH-Ar-12888); B: paratype, ovigerous female, 8.0 mm (OMNH-Ar-12891).