Cryptodius Moore, 1992 ( Moore 1992 : 913 )

Labay, Vjacheslav S., 2019, Review of amphipods of the genus Cryptodius Moore, 1992 (Amphipoda: Ochlesidae) from the coastal waters of Sakhalin Island (Far East of Russia), Zootaxa 4603 (3), pp. 501-519 : 503-504

Genus Cryptodius Moore, 1992 ( Moore 1992: 913)

Cryptodius Moore, 1992 ( Moore 1992: 913 — Berge et al. 1998: 244.— Kim & Hong 2014: 137.

Odius Liljeborg, 1865 : Gurjanova 1951: 496 (part).— Barnard & Karaman 1991: 397 (part).

Type species. Cryptodius kelleri ( Brüggen, 1907) : 478.

Species. Including the new species described here, Cryptodius contains 3 species ( Ariyama 2011, Brüggen 1907, Gurjanova 1938, Gurjanova 1951, Kim & Hong 2014, Moore 1992, new data): C. kelleri ( Brüggen, 1907) , C. sakhalinensis sp. nov. and C. unguidactylus Moore, 1992 .

Diagnosis (from Moore 1992, with additions). Body smooth. Pereon lacking a conspicuous narrow, mid-dorsal keel or carinated middorsally on pereon. Head telescoped into a pereon segment 1. Rostrum overriching antenna 1 peduncle segment 1. Eyes large, reniform. Antennae short. Antenna 1, peduncle segment 1 subequal to 2 an 3 together. Antenna 2, peduncle segment 4 and 5 subequal. Upper lip asymmetrically incised. Mandible elongate, spine row strong, molar below of level with palp origin, well developed, palp segment 1 small, segments 2 and 3 elongate, subequal. Maxilla 1, inner plate reduced, with 2–3 setae apically; outer plate conical, medial margin with curved dentate stout setae distally; palp 1-segmented, with 1–2 setae apically. Maxilliped, palp segment 2 produced medially, distally concave or not, segment 4 not reduced. Coxae 1–4 not shortened; coxa 1 triandular or concave anteriorly; coxae 2 and 3 distally truncate; coxa 4 with posterodistal lobe truncated obliquely to produce an acute posterior tooth. Pereopods dactylus with unguis. gnathopod 1 flagellar. Pereopod 1 (gnathopod 1) propodochelate, carpus and propodus elongate, subequal in length; dactylus bearing several long plumose setae. Pereopod 2 (gnathopod 2) broader than 1, merus with triangular lobe, propodus triangular, with long palm. Bases of pereopods 5–7 not bearing teeth or cusps. Uropod 1, rami subequal. Uropod 2 reaching or exceecling uropod 3, inner ramus longer than outer. Uropod 3, inner ramus longer than outer and subequal to peduncle. Telson ventrally boat-keeled, apex acutely rounded, entire or slightly incised.

Distribution. Marine waters of arctic and boreal part of Northern hemisphere ( Berge et al 1998, Gurjanova 1938, 1951, Kim & Hong 2014, Moore 1992).

Remarks. Moore (1992) allocated Odius kelleri Brüggen, 1907 as the type species of Cryptodius Moore, 1992 , that is a derivative of Odius Liljeborg, 1865 , alluding to this genus hitherto hidden identity. The main features of the genus after Moore (1992): pereon lacking a conspiciuous narrow, mid-dorsal keel; head telescoped into a peraeon segment 1; eyes large; antennae short; antenna 1, peduncle segment 1 subequal to 2 an 3 together; antenna 2, peduncle segment 4 and 5 subequal; epistome raised in a median keel; upper lip elongate, asymmetrically incised; mandible elongate, spine row strong, molar on level with palp origin, well developed, palp segment 1 small, segments 2 and 3 elongate, subequal; maxilla 1, inner plate reduced, few setose; outer plate conical, medial margin with curved dentate spines distally, setose proximally; palp 1-segmented; maxilla 2, inner plate with medial margin setulose, outer plate with lateral margin setulose; maxilliped, palp segment 2 produced medially, segment 4 not reduced, inner plate subequal to or longer than outer plate; coxae 1–4 not shortened; coxa 1 triangular; coxae 2 and 3 distally truncate; coxa 4 with posterodistal lobe truncated obliquely to produce an acute posterior tooth; gnathopods and pereopods 3–7 dactylus with unguis; gnathopod 1 flagellar, propodochelate, carpus and propodus elongate, subequal; dactylus bearing several long plumose setae and 2 unguinal spines distally; gnathopod 2 broader than 1, propodus triangular, with long palm, dactylus with accessory tooth on posterior margin; bases of pereopods 5–7 not bearing teeth or cusps; epimeral plates 2 and 3 posterodistal angles acute; uropod 1, rami subequal; uropod 2, inner ramus longer than outer; uropod 3, inner ramus longer than outer and subequal to peduncle; telson ventrally boatkeeled, apex acutely rounded, entire.

Berge et al. (1998: appendices 1 and 2) changed the diagnosis of the genus Cryptodius . It was added new main features—the structure of mandible, maxilliped, pereopods 1 and 2, uropod 2: “Attachment of mandible palp in relation to molar: … below”; “Mandible projection of the hingeline: … absent”; “Maxilliped palp article 2 distally: … concave”; “Pereopod 1 propodus: … at least as long as carpus”; “Uropod 2: … reaching or exceecling uropod 3”.

Features of the dorsal armament, maxilliped and telson of Cryptodius sakhalinensis sp. nov. indicate that this features is unstable and can not be used as a generic characteristic. With the addition of new species described here, the only stable features of the genus Cryptodius are signs of structure of pereopod 6 and pereopod 7 (basis smooth posteriorly), uropod 2 (reaching or exceecling uropod 3); telson (entire or slightly incised).