Six species of Grandidierella collected from the Ryukyu Archipelago in Japan with descriptions of four new species (Crustacea: Amphipoda: Aoridae) Author Ariyama, Hiroyuki text Zootaxa 2020 2020-07-09 4810 1 1 44 journal article 10.11646/zootaxa.4810.1.1 1175-5326 3936945 BBD6D565-039A-47C7-9110-653DD75EBDBF Grandidierella nana sp. nov. [Japanese name: Chibi-dorosokoebi, new] ( Figs 25–29 ) Type material. Holotype : male, 2.6 mm (OMNH-Ar-11546), Funaura , Iriomote Island , Okinawa Prefecture , 24°23'49"N , 123°49'31"E ( Fig. 1G ), middle intertidal, fine sand bottom, 18 July 2015 , coll. H. Ariyama. Paratypes : 3 males , 2.3, 2.0, 1.8 mm (OMNH-Ar-11547–11549) and 2 ovigerous females, 3.2, 2.7 mm (OMNH-Ar-11550, 11551), same data as holotype; male, 2.3 mm and ovigerous female, 3.4 mm (OMNH-Ar-11552, 11553), mouth of Nakama River , Iriomote Island , Okinawa Prefecture , 24°16'50"N , 123°52'53"E ( Fig. 1I ), upper–middle intertidal, sandy mud bottom with gravel, 15 July 2015 , coll. H. Ariyama. Type locality. Funaura in Iriomote Island , Okinawa Prefecture , Japan . Etymology. From the Greek nanus , -a, -num (= very small), referring to the size of the species. Diagnosis. Male pereon , ventral process absent. Male gnathopod 1 , posterodistal corners of ischium and merus without projection; carpus wide, with 2 teeth posterodistally; propodus curved posteriorly, posterodistal corner swollen. Male gnathopod 2 , coxa without posteromedial projection; basis curved anteriorly; carpus longer than propodus; propodus with a few robust setae on posterodistal corner and posterior margin. Uropod 1 peduncle with inter-ramal process. Description of male. Based on holotype , male, 2.6 mm (OMNH-Ar-11546). Head ( Figs 25 , 26 ) depressed dorsoventrally. Eyes medium-sized, about quarter length of head. Antenna 1 slender, about 0.6 times as long as body; length ratio of peduncular articles 1–3 1:1.15:0.4, article 1 with 4 ventral robust setae; accessory flagellum vestigial, uniarticulate; primary flagellum with 11 articles, terminal article minute, posterodistal corners of articles 5–10 each bearing aesthetasc. Antenna 2 stout, length about 0.45 times as long as body; length ratio of peduncular articles 3–5 1:2.9:2.8, article 3 with 2 medial robust setae; flagellum short, consisting of 3 normal and 1 minute articles, articles 2, 3 with 3 and 2 robust setae, respectively. Upper lip slightly hollowed ventrally, bearing many thin setae. Mandibles with length ratio of palp articles 1–3 1:1.4:1.2, articles 1, 2 each with 2 setae, article 3 clavate, setose distally; incisor with 4 and 5 cusps in left and right, respectively, lacinia mobilis with 3 cusps, 5 accessory setae present. Lower lip , distal margin of outer lobe slightly projected in middle, apical parts of outer and inner lobes covered with thin setae. Maxilla 1 , outer plate with 12 distal robust setae, palp article 2 bearing 5 robust and several slender setae apically. Maxilla 2 with inner plate setose on distal and medial margins, lacking mediofacial row of setae, outer plate setose on distal margin. Maxilliped , distal part of inner plate setose, with 3 robust setae; outer plate bearing 7 long-to-short robust setae mediodistally; palp article 2 long, articles 2, 3 with several setae. Pereon ( Fig. 27 ). Ventral surface lacking process. Gnathopod 1 , coxa roundish trapezoidal; basis wide, lateral surface with ridge, posterior margin a little convex; ischium short, without posterodistal projection; merus posterodistal margin bearing a few setae, lacking projection; carpus ovoid, length about 1.2 times width, distal margin with small blunt tooth, posterodistal corner with large sharp tooth, posterior margin setose moderately; propodus curved posteriorly, posterodistal corner swollen roundly, setose; dactylus short, slightly curved posteriorly, posterior margin without denticle. Gnathopod 2 , coxa trapezoidal; basis slender, curved anteriorly, with ridge anterolaterally; merus posterodistal margin setose; carpus, distal half of posterior margin densely setose; propodus 0.8 times as long as carpus, posterodistal corner and posterior margin with 2 and 1 short robust setae, respectively; dactylus short, curved posteriorly, posterior margin with 2 denticles. Pereopods 3 and 4 , pereopod 3 slightly longer than pereopod 4; coxae trapezoidal; bases long; meri wide, a little dilated distally; carpi shorter than meri; propodi and dactyli narrow. Pereopod 5 shorter than pereopod 4; coxa bilobed; basis rectangular, posteroproximal corner angular, anterior margin with several setae, posterior margin bearing a few short setae and long plumose seta; merus with long thick seta each on anterodistal and posterodiatal corners; carpus bearing anterodistal thick seta and posterodistal robust seta; propodus with 2 lateral and 2 posterodistal robust setae; dactylus short, strongly curved. Pereopod 6 about 1.75 times as long as pereopod 5; coxa short, slightly bilobed; basis rectangular, posteroproximal corner angular, anterior margin with several short setae, posterior margin with many plumose setae; merus anterodistal corner with robust seta, posterior margin and posterodistal corner each bearing thick seta; carpus with lateral robust seta, posterodistal corner bearing 1 robust and 1 thick setae; propodus with 3 anterior robust setae, posterodistal corner setose; dactylus curved. Pereopod 7 about 1.2 times as long as pereopod 6; coxa short, slightly bilobed; basis rectangular, posteroproximal corner angular, anterior margin with several short setae and plumose seta, posterior margin bearing many plumose setae and several short setae; merus anterodistal corner with robust seta, posterior margin bearing 3 thick setae; carpus with lateral robust seta, posterodistal corner bearing 1 robust and 1 thick setae; propodus with 2 anterior robust setae and posterior thick seta, posterodistal corner setose; dactylus curved. FIGURE 25. Grandidierella nana sp. nov. Holotype, male, 2.6 mm (OMNH-Ar-11546). Habitus. Pleon ( Fig. 28 ). Epimeral plates 1–3 rounded posteroventrally, without setae, ventral margins bare ( Fig. 25 ). Pleopods , each peduncle bearing several plumose setae and 2 coupling hooks; inner ramus longer than outer, both rami each with 6–7 articles. Uropod 1 , dorsal surface of peduncle bearing 2 lateral and 3 medial robust setae, ventrodistal end with inter-ramal process; both rami shorter than peduncle, outer ramus subequal to inner ramus, former with 4 terminal robust setae, latter bearing 1 dorsomedial and 3 terminal robust setae. Uropod 2 about half length of uropod 1; peduncle dorsal surface with 1 laterodistal and 1 mediodistal robust setae; both rami shorter than peduncle, outer ramus shorter than inner ramus, former with 2 terminal robust setae, latter bearing 3 terminal robust setae. Uropod 3 about 0.55 times as long as uropod 2; peduncle slightly wider than long, swollen medially, lateral margin with seta; single ramus almost same length as peduncle, with tiny second article and 1 lateral and 4–5 terminal setae. Telson wider than long, laterodistal corners each with 2 setae. Description of female. Based on paratype , ovigerous female, 3.2 mm (OMNH-Ar-11550). Gnathopod 1 ( Fig. 28 F-G1), coxa trapezoidal; basis almost straight; ischium and merus short, both lacking projection; carpus wide, posterior margin without projection, setose; propodus about 0.9 times as long as carpus, posterior margin with 2 robust setae; dactylus slightly curved posteriorly, posterior margin with 3 denticles. Gnathopod 2 ( Fig. 28 F-G2) almost same as that of holotype , male, 2.6 mm (OMNH-Ar-11546) except for oostegite, but coxa longer, basis almost straight, carpus shorter. Variation. Paratype , small male, 1.8 mm (OMNH-Ar-11549). Gnathopod 1 ( Fig. 28 SM-G1) almost same as that of holotype , male, 2.6 mm (OMNH-Ar-11546), but propodus wider, posterior margin of dactylus with 2 denticles. Coloration in recently fixed specimen ( Fig. 29 ). Eyes dark brown; dorsal surfaces of head, pereonites and pleonites yellowish light brown. Antenna 1 peduncles and proximal part of antenna 2 peduncular article 4 also yellowish light brown. Other parts white. Remarks. Grandidierella nana sp. nov. is a small species (maximum BL: 2.6 mm in male and 3.4 mm in female). The wide and short carpus (length:width=1:1.2) of the male gnathopod 1 in adults is unique in the genus. Grandidierella propodentata Moore, 1986 and G. rhizophorae Myers, 2009 both from Australia have a relatively wide and short carpus (length:width=1:1.4) of the male gnathopod 1; however, G. propodentata possesses a posteroproximal tooth on the male gnathopod 1 propodus and G. rhizophorae has a single posterodistal tooth on the male gnathopod 1 carpus. FIGURE 26. Grandidierella nana sp. nov. Holotype, male, 2.6 mm (OMNH-Ar-11546). Scales: 0.05 mm. FIGURE 27. Grandidierella nana sp. nov. Holotype, male, 2.6 mm (OMNH-Ar-11546). Scales: 0.05 mm. FIGURE 28. Grandidierella nana sp. nov. All except for F and SM: holotype, male, 2.6 mm (OMNH-Ar-11546); F, paratype, ovigerous female, 3.2 mm (OMNH-Ar-11550); SM, paratype, male, 1.8 mm (OMNH-Ar-11549). Scales: 0.05 mm. Habitat. Fine sand bottom in the middle intertidal zone, marine; sandy mud bottom with gravel in the up-per–middle intertidal zone, brackish. Distribution. Japan : Iriomote Island (present study).