Grandidierella pseudosakaensis, Ariyama, 2020

Ariyama, Hiroyuki, 2020, Six species of Grandidierella collected from the Ryukyu Archipelago in Japan with descriptions of four new species (Crustacea: Amphipoda: Aoridae), Zootaxa 4810 (1), pp. 1-44 : 34-40

Grandidierella pseudosakaensis sp. nov.

[Japanese name: Nise-ōsaka-dorosokoebi, new]

( Figs 30–36 )

Type material. Holotype: male, 3.9 mm (OMNH-Ar-11554), mouth of Nakara River, Iriomote Island , Okinawa Prefecture, 24°21'11"N, 123°45'12"E ( Fig. 1H ), upper–middle intertidal, sandy mud bottom under stones and soft sandstone, 16 July 2015, coll. H. Ariyama. Paratypes: 3 males, 4.0, 3.5, 3.1 mm (OMNH-Ar-11555–11557) and 2 ovigerous females, 4.5, 3.5 mm (OMNH-Ar-11558, 11559), same data as holotype .

Material for comparison ( Grandidierella osakaensis Ariyama, 1996 ). Holotype, male, 6.9 mm (OMNH-Ar- 3855), mouth of Yodo River, Osaka City , 34°41'N, 135°25'E, 11 May 1991, coll. H. Ariyama. Allotype, female, 7.1 mm (OMNH-Ar-3856), same data as holotype. Paratypes: male, 6.1 mm (OMNH-Ar-3857), same data as holotype; male, 6.1 mm [corrected from 7.5 mm] (OMNH-Ar-3858) and female, 6.9 mm (OMNH-Ar-3859), mouth of Higashi River in Misaki , Osaka Prefecture, 20 February 1992, coll. H. Ariyama ( Ariyama 1996) . Male, 5.8 mm (OMNH- Ar-10297) and female, 6.3 mm (OMNH-Ar-10298), mouth of Tadori River in Bishamon, Minami-shimoura-cho, Miura City , Kanagawa Prefecture, 35°08'35"N, 139°39'49"E, 7 June 2015, coll. M. Taru ; male, 7.0 mm (OMNH- Ar-10301) and ovigerous female, 6.7 mm (OMNH-Ar-10302), anchialine pool in Okada-shinkai, Izu Oshima Island ( Oshima Town ), Tokyo Prefecture, 34°47'41"N, 139°21'34"E, 31 March 2017, coll. O. Hoshino ; male, 4.9 mm (OMNHAr-10299) and ovigerous female, 4.2 mm (OMNHAr-10300), mouth of Aono River in Minato, Minami-izu Town , Shizuoka Prefecture, 34°38'05"N, 138°53'11"E, 31 August 2014, coll. M. Taru ( Ariyama & Taru 2017) . Two males, 4.7, 4.0 mm (OMNH-Ar-11560, 11561), ovigerous female, 4.6 mm (OMNH-Ar-11562) and female, 4.0 mm (OMNH-Ar-11563), mouth of Yodo River, Osaka City , 34°41'16"N, 35°25'19"E, lower intertidal, mud under stones in artificial tidepool, 29 May 2017, coll. H. Ariyama.

Type locality. Mouth of Nakama River in Iriomote Island, Okinawa Prefecture, Japan .

Etymology. From the Greek pseud (= false) + osakaensis (closely related species).

Diagnosis. Male pereon, ventral process absent. Male gnathopod 1, ischium lacking posterodistal projection, merus posterodistal corner with 2 projections, posterior surface sparsely rugose; carpus with 3 teeth posterodistally, middle and proximal teeth large; propodus almost straight, widened in middle. Male gnathopod 2, coxa without posteromedial projection; basis slightly curved anteriorly; carpus longer than propodus; propodus with a few robust setae on posterodistal corner and posterior margin. Uropod 1 peduncle lacking inter-ramal process.

Description of male. Based on holotype, male, 3.9 mm (OMNH-Ar-11554), paratype, male, 4.0 mm (OMNH- Ar-11555) for lower lip and uropod 1, and paratype, male, 3.5 mm (OMNH-Ar-11556) for telson .

Head ( Figs 30 , 31 ). Eyes small, about 20% length of head. Antenna 1 slender, about 55% length of body; length ratio of peduncular articles 1–3 1:1.05:0.45, article 1 with 3 ventral robust setae; accessory flagellum very short, minutely 2-articulate; primary flagellum with 12 articles, terminal article minute. Antenna 2 relatively stout, length about 0.45 times as long as body; length ratio of peduncular articles 3–5 1:2.1:1.9, article 3 with 2 lateral and 4 medial robust setae; flagellum short, consisting of 5 normal and 1 minute articles, articles 3–5 with 1, 2, 2 robust setae, respectively. Upper lip rounded ventrally, bearing many thin setae. Mandibles with length ratio of palp articles 1–3 1:1.25:1.3, articles 1, 2 with 1 and 6 setae, respectively, article 3 clavate, densely setose distally; incisor with 5 cusps, lacinia mobilis with 4 and 3 cusps in left and right, respectively, 7 accessory setae present. Lower lip, mediodistal corner of outer lobe slightly projected, apical parts of outer and inner lobes covered with thin setae. Maxilla 1, outer plate with 9 distal robust setae, palp article 2 bearing 5 robust and 3 slender setae apically. Maxilla 2, inner plate bearing distal and medial setae and mediofacial row of setae, outer plate setose on distal margin. Maxilliped, distal part of inner plate setose, with 3 quadrate and 1 narrow robust setae; outer plate bearing 9 long-to-short robust setae mediodistally; palp article 2 long, setose medially, article 3 setose distally.

Pereon ( Fig. 32 ). Ventral surface lacking process. Gnathopod 1, coxa trapezoidal; basis very wide, lateral surface with ridge, posterior margin convex; ischium short, posterodistal corner lacking projection; merus posterodistal corner projected, distal margin with small projection and several setae, posterior surface sparsely rugose; carpus wide, length about 1.55 times width, with 3 teeth posterodistally, distal tooth small, middle and proximal teeth large, posterior margin sparsely setose; propodus almost straight, posterior margin swollen in middle, anterodistal corner and posterior margin setose; dactylus short, slightly curved posteriorly, posterior margin with single denticle. Gnathopod 2, coxa trapezoidal; basis slender, slightly curved anteriorly; merus posterodistal margin setose; carpus relatively wide, posterior margin densely setose; propodus 0.7 times as long as carpus, posterodistal corner and posterior margin with 3 and 2 short robust setae, respectively; dactylus short, curved posteriorly, posterior margin with 4 denticles. Pereopods 3 and 4, pereopod 3 slightly longer than pereopod 4; coxa 3 trapezoidal; bases long; meri wide, slightly dilated distally; carpi shorter than meri; propodi and dactyli narrow. Pereopod 5 shorter than pereopod 4; coxa bilobed; basis rectangular, posteroproximal corner projected, anterior margin with proximal plumose seta and several setae, posterior margin bearing several setae; merus with long thick seta each on posterior margin and anterodistal and posterodiatal corners; carpus bearing anterodistal thick seta and posterior and posterodistal robust setae; propodus with 3 lateral and 1 posterodistal robust setae; dactylus short, strongly curved. Pereopod 6 about 1.7 times as long as pereopod 5; coxa short, slightly bilobed; basis rectangular, posteroproximal corner roundly projected, anterior margin with 4 proximal and 1 distal plumose setae and several setae, posterior margin with many plumose setae; ischium laterodistal surface bearing plumose seta; merus posterior margin with 3 thick setae, posterodistal corner bearing 1 robust and 1 thick setae; carpus with 3 lateral robust setae, posterodistal corner bearing 1 robust and 1 thick setae; propodus with 5 anterior robust setae, posterodistal corner setose; dactylus curved. Pereopod 7 about 1.1 times as long as pereopod 6; coxa short, slightly bilobed; basis rectangular, posteroproximal corner angular, anterior margin with 1 proximal and several distal plumose setae, posterior margin bearing many plumose setae; ischium laterodistal surface bearing plumose seta; merus posterior margin bearing 3 thick setae, posterodistal corner with 1 robust and 1 thick setae; carpus with 2 lateral robust setae, anterodistal corner with thick seta, posterodistal corner bearing 1 robust and 1 thick setae; propodus with 4 anterior robust setae and 2 posterior thick seta, posterodistal corner setose; dactylus curved.

Pleon ( Fig. 33 ). Epimeral plates 1–3 each with long thick seta on posteroventral corner, ventral margins bare ( Fig. 30 ). Pleopods, each peduncle bearing many plumose setae and 2 coupling hooks; inner ramus longer than outer, outer rami with 8–10 articles, inner rami with 9–10 articles. Uropod 1, dorsal surface of peduncle bearing 2 lateral and 3 medial robust setae, ventrodistal end lacking inter-ramal process; both rami shorter than peduncle, outer ramus slightly shorter than inner ramus, former with 3 dorsal and 4 terminal robust setae, latter bearing 1 dorsolateral, 2 dorsomedial and 4 terminal robust setae. Uropod 2 about half length of uropod 1; peduncle dorsal surface with 1 lateral, 1 laterodistal and 1 mediodistal robust setae; both rami shorter than peduncle, outer ramus shorter than inner ramus, former with 1 dorsal and 4 terminal robust setae, latter bearing 1 dorsolateral, 1 dorsomedial and 4 terminal robust setae. Uropod 3 about half length of uropod 2; peduncle slightly wider than long, swollen medially, bare; single ramus longer than peduncle, with tiny second article and 8 setae. Telson wider than long, laterodistal corners each with 2 setae.

Description of female. Based on paratype, ovigerous female, 4.5 mm (OMNH-Ar-11558). Antenna 2 ( Fig. 33 F-A2) similar to that of holotype, male, 3.9 mm (OMNH-Ar-11554), but flagellar articles 2–5 with 1, 2, 2, 2 robust setae, respectively. Gnathopod 1 ( Fig. 33 F-G1), coxa trapezoidal; basis relatively wide; ischium and merus short, both without projection; carpus wide, posterior margin with single robust seta and many long setae, lacking projection; propodus about 1.15 times as long as carpus, posterodistal corner and posterior margin with 3 and 1 robust setae, respectively; dactylus slightly curved posteriorly, posterior margin with 4 denticles. Gnathopod 2 ( Fig. 33 F-G2) resembling that of holotype, male, 3.9 mm (OMNH-Ar-11554) except for oostegite, but coxa longer, basis wider and almost straight, carpus shorter.

Coloration in recently fixed specimen ( Fig. 34 ). Eyes dark brown; head, pereonites and pleonites brown; antennae mostly pale red; other appendages whitish, but propodi of pereopods 3 and 4 each with red vermiform spot.

Remarks. Grandidierella pseudosakaensis sp. nov. is characterized by the male gnathopod 1 with a posterodistal projection on the merus and three distinct teeth on the propodus and the uropod 1 without an inter-ramal process. This new species shares these characters only with G. osakaensis from Tokyo–Shizuoka, Osaka and Shimane Prefectures in Japan ( Ariyama & Taru 2017). But this new species can be distinguished from G. osakaensis by the ischium of the male gnathopod 1 lacking a posterodistal projection. Large or middle-sized males of G osakaensis always have a distinct projection on the ischium ( Ariyama 1996, Ariyama & Taru 2017), and small males have an indistinct projection ( Fig. 35 ). Both species are also different in their body sizes and the growth process of the male gnathopods. Maximum sizes of G. pseudosakaensis are 4.0 mm in male and 4.5 mm in female, whereas those of G. osakaensis are 7.0 mm in male and 7.1 mm in female. Relationship of the body length with “length of proximal tooth / length of middle tooth” in the male gnathopod 1 and relationship of the body length with “propodus length / carpus length” in the male gnathopod 2 apparently disagree in both species ( Figs 35 , 36 ), viz. G. pseudosakaensis develops to the adult form in the far smaller size than G. osakaensis . In addition, the shape of the male gnathopod 1 in G. pseudosakaensis also resembles those in G. dentimera Myers, 1970 and G. palama J.L. Barnard, 1977 both from Hawaii (probably different growth stages of the same species), although the presence or absence of an inter-ramal process on the uropod 1 peduncle is unknown. However, G. pseudosakaensis differs from the latter two species in the shorter merus of the male gnathopod 2 and the wider propodus of the female gnathopod 1.

Habitat. Sandy mud bottom under stones and soft sandstone in the upper–middle intertidal zone, brackish. This species occurs together with G. contigua .

Distribution. Japan: Iriomote Island (present study).

Figures

FIGURE 1. Map showing collecting sites of the examined specimens in the Ryukyu Archipelago.

FIGURE 30. Grandidierella pseudosakaensis sp. nov. Holotype, male, 3.9 mm (OMNH-Ar-11554). Habitus.

FIGURE 31. Grandidierella pseudosakaensis sp. nov. All but M1, holotype, male, 3.9 mm (OMNH-Ar-11554); M1, paratype, male, 4.0 mm (OMNH-Ar-11555). Scales: 0.05 mm.

FIGURE 32. Grandidierella pseudosakaensis sp. nov. Holotype, male, 3.9 mm (OMNH-Ar-11554). Scales: 0.1 mm.

FIGURE 33. Grandidierella pseudosakaensis sp. nov. All except for F, M1 and M2: holotype, male, 3.9 mm (OMNH-Ar- 11554); F, paratype, ovigerous female, 4.5 mm (OMNH-Ar-11558); M1, paratype, male, 4.0 mm (OMNH-Ar-11555); M2, paratype, male, 3.5 mm (OMNH-Ar-11556). Scales: 0.1 mm.

FIGURE 34. Grandidierella pseudosakaensis sp. nov. Photograph of paratype, male, 3.5 mm (OMNH-Ar-11556), fixed specimen (6.5 hours after fixation).

FIGURE 35. Grandidierella pseudosakaensis sp. nov. and G. osakaensis Ariyama, 1996. Comparison of male gnathopods. Grandidierella pseudosakaensis: paratypes, males, 3.5, 3.1 mm (OMNH-Ar-11556, 11557); G. osakaensis: males, 4.7, 4.0 mm (OMNH-Ar-11560, 11561). Scales: 0.1 mm.

FIGURE 36. Grandidierella pseudosakaensis sp. nov. and G. osakaensis Ariyama, 1996. Relationship of body length with “length of proximal tooth / length of middle tooth” in male gnathopod 1 (left) and relationship of body length with “propodus length / carpus length” in male gnathopod 2 (right).