Guernea ezoensis Ishimaru, 1987

Sidorov, Dmitry A., 2023, On a small collection of amphipods (Crustacea, Amphipoda) from the Lesser Kuril Chain, Amurian Zoological Journal XV (1), pp. 42-49 : 43-47

Guernea ezoensis Ishimaru, 1987

( Figs. 1–3 )

Guernea ezoensis Ishimaru, 1987: p. 1404 , Figs. 7–11 (original description). — Hirayama, Takeuchi 1993: p. 142. — Kim et al. 2011: p. 5 , Figs. 2A , 3 -5.

Material examined (new record). Russia, Yuri Is. (sta. k28), 16♀ (oostegites developed,some brooding 15-22 eggs), 2♂ (BL = up to 2.8 mm), Shirokaya Bay , 12.08.2013, coll. Sidorov D. A., seashore, Karaman-Chappuis pits in finely rolled pebbles, DAS 1-14/01 .

Description. Female, ovigerous with 19 eggs (B = 2.25 mm). GENERAL BODY MORPHOLOGY ( Figs. 1 : a–c, 3: a–g, 3: l). Body stout, strongly calcified; alive coloration whitish, translucent. Head subtriangular, rostrum indistinct; lateral cephalic lobe broadly rounded, inferior antennal sinus moderate; eyes pigmented, relatively small, composed of 28 ommatidia. Urosomite I with weak triple dorsal crest, bearing upper group of setae and lower group of 2 spines, urosomites II–III (coalesced) with double dorsal crest, almost evenly rounded and sloping forwards, bearing 4 spines accompanied with setae. Coxa IV curved; coxa V broad, posterior lobe evenly rounded; coxa VII deep, anterior lobe absent. Gills of coxae II– V large sacs, of coxa VI smaller, absent on coxa VII. Oostegites II – V (brood plates) well-developed, narrow, plate V the smallest.

Epimera I–III with distinctly inward forward anteroventral lobe. Telson 1.4 times as long as broad, deeply cleft, with a few minute setae along lateral margins, lobes apically with 1 spine each. ANTENNAE ( Figs 1a, 1d, 1e ). Antenna I about 15% of body length, peduncle articles in relation 1:0.6:0.3, flagellum of 6 articles, a couple of terminal flagellar articles with oblong aesthetasc each; accessory flagellum 1-segmented, reduced. Antenna II 90% of antenna I length, peduncle articles (4 + 5) about twice longer than flagellum, bearing rare long setae on ventral face; flagellum of 4 articles, modestly equipped with short setae; gland cone reaches one-third of article 4. MOUTH PARTS ( Figs. 2 : a–h). Mandibular incisors with 2 weak teeth, molar without a seta. Maxilla I outer lobe with 9 pectinate (or bifid) spines, palp 2-segmented, slightly asymmetric, distally with group of setae. GNATHOPODS ( Figs 1f, 1g ). Gnathopod II longer than gnathopod I; propodi (article 6) of both gnathopods with palmar angle defined and armed with 4 distally-notched spines. PEREOPODS ( Figs. 1 : a, 3: a–e), without peculiarities. PLEOPODS AND UROPODS ( Figs. 1 : a, 3: h–l), ordinary, shaped and setose like in the original description.

Sexual dimorphism. Pronounced, expressed in the larger body size in females, in contrast with two male specimens of 2.2 mm body length ( Figs. 2 : i–m). Sexually dimorphic appendages as antenna II long, flagellum with 20 articles; among other features females differ by lacking long plumose setae on uropod III rami and first peduncular article of antenna I richer setose on ventral margin.

Variation. Not observed.

Remarks. The examined specimens correspond well with the earlier descriptions of G. ezoensis by ( Ishimaru 1987) and ( Kim et al. 2011), however, it differ in a number of minor characters: the lower edge of head without a pronounced cheek, the posterior lobe of coxa V is distinctly shallow, gland cone of antenna II noticeably exceeding article 3 in both sexes, telson lacking sub-apical spines on dorsal surface (replaced with setae), both gnathopods with 4 spines at palmar angle, male antenna II weakly setose, mouthparts slightly differ in the armament pattern.

Distribution and ecology. Guernea ezoensis is a common gammaridean amphipod inhabiting predominantly intertidal biotopes (recorded at depths from 0 to 40 m) in the Far Eastern marine region ( Table 1 ). Previously recorded from the northern Japan ( Ishimaru 1987) and around the Korean Peninsula and Jejudo Isl. ( Kim et al. 2011), the finding of the species in the Matsukawa-ura Lagoon ( Hirayama, Takeuchi 1993) deserves attention. Besides the above-mentioned locations, the species was observed in tide pools among finely rolled pebbles from Yuri Isl., Southern Kurils, where it occurs together with unidentified pontogeneiid amphipod juveniles Paramoera sp.

Figures

Fig. 1. Guernea ezoensis Ishimaru, 1987, female, 2.25 mm: a — habitus (left side view); b — head; c — urosome (left side view); d — antenna I; e — antenna II; f — gnathopod I; g — gnathopod II. Scale bars: 0.2 mm Рис. 1. Guernea ezoensis Ishimaru, 1987, самка, 2.25 мм: a — габитус (виà сбоку); b — гоΛова; c — уросома (виà сбоку); d — антенна I; e — антенна II; f — гнатопоà I; g — гнатопоà II. Λинейки 0.2 мм

Fig. 2. Guernea ezoensis Ishimaru, 1987, female, 2.25 mm (a-h): a — lower lip; b — upper lip; c, d — mandibles; e — maxilla I (right); f — palp of maxilla I (left); g — maxilla II; h — maxilliped; male, 2.2 mm (i-m): i — antenna I; j — antenna II; k — uropod I; l — uropod III; m — telson. Scale bars: 0.2 mm Рис. 2. Guernea ezoensis Ishimaru, 1987, самка, 2.25 мм (a-h): a — нижняя губа; b — верхняя губа; c, d — манÃибуΛы; e — максиΛΛа I (правая); f — щупик максиΛΛы I (Λевый); g — максиΛΛа II; h — ногочеΛюсть; самец, 2.2 мм (i-m): i — антенна I; j — антенна II; k — уропоà I; l — уропоà III; m — теΛьсон. Λинейки 0.2 мм

Fig. 3. Guernea ezoensis Ishimaru, 1987, female, 2.25 mm: a — pereopod III; b — pereopod IV; c — pereopod V; d — pereopod VI; e — pereopod VII; f — urosome (dorsally); g — epimeral plates; h — pleopod II; i — uropod I; j — uropod II; k — uropod III; l — telson. Scale bars: 0.2 mm Рис. 3. Guernea ezoensis Ishimaru, 1987, самка, 2.25 мм: a — переопоà III; b — переопоà IV; c — переопоà V; d — переопоà VI; e — переопоà VII; f — уросома (виà сверху); g — эпимераΛьные пΛастинки; h — пΛеопоà II; i — уропоà I; j — уропоà II; k — уропоà III; l — теΛьсон. Λинейки 0.2 мм

Tables

Table 1 Distribution and habitat preferences of Guernea ezoensis, (n) — number of collected specimens ТабΛица 1 Распространение и местообитания Guernea ezoensis, (n) — коΛичество собранных экземпΛяров

Locality	(n)	Method of capture	Depth range (m)	Substrate	References
Hokkaido, Japanese Archipelago	10	light trap	0–40	sand, mud, gravel, oyster beds	Ishimaru (1987)
Honshu, Japanese Archipelago	—	plankton net	—	—	Hirayama, Takeuchi (1993)
Korean Peninsula	>500	light trap / sieving	1–12	sand, mud	Kim et al. (2011)
Southern Kurils	18	Karaman-Chappuis pits	littoral	pebbles	Present study