Lobatoradarea Ariyama, 2025

Lobatoradarea Ariyama , gen. nov.

[New Japanese name: Udenaga-yokokoebi-zoku]

Type species. Lobatoradarea littoralis Ariyama , sp. nov.

Diagnosis. Body slender, weakly compressed laterally, integument lacking scales; posterodorsal margin of pereonite 7 projected or not, posterodorsal margins of pleonites 1, 2 usually projected. Head with anteroventral corner acutely or slightly produced, rostrum distinct. Antennae long, slender, flagella lacking calceoli; antenna 1 peduncular articles progressively shorter, dorsodistal and ventrodistal corners of article 2 projected, accessory flagellum 1-articulate; antenna 2 peduncular articles 3–5 progressively longer. Mandible, molar triturative, columnar; palp article 2 longer than article 3. Lower lip with inner lobes rounded proximally. Maxilla 1, inner plate with many medial setae, outer plate with many robust setae distally; palp article 1 shorter than article 2, article 2 bearing distal robust setae. Maxilla 2, inner plate wider than outer plate; inner plate with facial row of many setae and medial setae, outer plate bearing distal setae. Coxae medium length, margins usually with small notches; coxa 1 with anterodistal corner rounded, coxa 4 excavated posteroproximally, coxae 5, 6 bilobed; gills present on coxae 2–7, oostegites present on female coxae 2–5. Gnathopod 1 short, subchelate; propodus as long as or slightly longer than carpus, palm oblique. Gnathopod 2 much longer than gnathopod 1, subchelate, sexual dimorphism indistinct; carpus and propodus elongate, with many short posterior setae, propodus longer than carpus, palm oblique, dactylus short. Pereopods 3–7 slender, dactyli smooth or with a minute projection on inner margins; laterodistal margins of bases and ischia in pereopods 3, 4 each with a semicircular lobe; bases of pereopods 5–7 lobate, with posterior margins serrated. Epimeral plates 1–3, posteroventral corners usually produced. Pleopod 3, peduncle bearing several robust setae on posteromedial surface. Uropods 1–3 progressively shorter, outer rami shorter than inner rami; uropods 1, 2 similar, both rami usually with dorsolateral, dorsomedial and terminal robust setae; uropod 3, both rami lanceolate in dorsal view, with dorsolateral and dorsomedial robust setae. Telson longer than wide, entire, but sometimes with 1–4 small notches; distal margin rounded or truncated.

Etymology. From the Latin lobato (=lobate) and Oradarea (closely related genus), referring to the lower lip with inner lobes. Gender: feminine.

Included species (11 species). Lobatoradarea angulata Ariyama & Kodama , sp. nov.; L. anko Ariyama & Hoshino , sp. nov.; L. coccina Ariyama, Kohtsuka & Hoshino , sp. nov.; L. inermis Ariyama, Kohtsuka & Kodama , sp. nov.; L. kagoshimensis Ariyama & Kodama , sp. nov.; L. lignorum Ariyama & Moritaki , sp. nov.; L. littoralis Ariyama , sp. nov.; L. longimana ( Boeck, 1871) , comb. nov.; L. obliquua Ariyama & Kodama , sp. nov.; and L. subinermis Ariyama & Kohtsuka , sp. nov.; and L. thermicola Ariyama & Chen , sp. nov.

Remarks. The most distinctive character of Lobatoradarea gen. nov. is the presence of inner lobes of the lower lip, and this new genus can be distinguished from Oradarea using this character. The inner lobes are unique in having a shape that is rounded proximally, whereas they are rounded distally in typical amphipods (if present). Oradarea longimana is here transferred to Lobatoradarea owing to exhibiting such a lower lip ( Boeck 1876, Shoemaker 1930). Leptamphopus novaezealandiae sensu Nagata (1965) has “lower lip bearing well developed inner lobes”, so this species also represents a member of Lobatoradarea .

Another distinctive character of the new genus is the gnathopod 2 with elongate carpus and propodus in both sexes. Besides Oradarea , Bouvierella Chevreux, 1900 and Leptamphopus Sars, 1895 in Calliopiidae , the genera Bathyschraderia Dahl, 1959 , Djerboa Chevreux, 1906 , Luckia Bellan-Santini & Thurston, 1996 , and Schraderia Pfeffer, 1888 in Pontogeneiidae Stebbing, 1906 also share such a gnathopod 2. Morphological differences between Lobatoradarea and other related genera are summarized in Table 1. Lobatoradarea is most close to Oradarea , and all the genera except Lobatoradarea never possess such inner lobes of the lower lip.

The semicircular lobes on the laterodistal margins of bases and ischia of pereopods 3 and 4 may be also distinctive, and all species of Lobatoradarea including L. longimana have this character, although species of the related genera shown in Table 1 generally do not have the character except for Oradarea shoemakeri Pirlot, 1934 [indistinct] and Luckia striki Bellan-Santini & Thurston, 1996 . In addition, the presence of the gill on coxa 7 and the robust setae on pleopod 3 peduncle seems to also be characteristic; however, presence or absence of them have not been noted in all the studies on the related genera.

Distribution. Only in the Northern Hemisphere: Japan (present study); Arctic ( Boeck 1871, Gurjanova 1951), Northwest Atlantic ( Shoemaker 1930) and Northeast Pacific ( Shaw 1989, Thomas & McCann 1995, Bousfield & Hendrycks 1997). Depth range: 0–2200 m.