Guernea nullispina Hirayama, 1985

Kim, Young-Hyo, Hendrycks, Ed A. & Lee, Kyung-Sook, 2011, The genus Guernea Chevreux, 1887 from Korean waters (Crustacea: Amphipoda: Dexaminidae), Zootaxa 3104, pp. 1-25 : 21-24

Guernea nullispina Hirayama, 1985

(Korean Name: Min-ga-si-but-eun-kko-ri-yeop-sae-u, new) ( Figs. 2 D, 14–15)

Guernea (Prinassus) nullispina Hirayama, 1985 , p. 18, figs. 134–136.

Material examined. 24 3, Anpo, Yeosu-si, 20 March 2004; 1 3, Doyang, Goheung-gun, 7 July, 2005; 4 3, Yonggipo, Baengnyeongdo Is., 12 July 2006; 2 3, Yongdong-ri, Goheung-gun, 22 June 2008.

Type locality. Tomioka Bay, Kyushu, Japan.

Description. Male. Body ( Figs. 2 D, 14A) slender, small, about 2.7 mm long, strongly chitinized; cephalon slightly longer than pereonites 1–2 combined; eye small, round, black; lateral cephalic lobe round, produced forward; pereonites smooth; pleonite 1 ( Fig. 14 B) broader than pleonites 2 and 3, with 1 ventral and 2 anterodistal setae; pleonite 2 subequal in width to pleonite 3, ventral margin rounded, with 6–7 setae; urosomite 1 with characteristic strong dorsal carina, gradually rising dorsodistally well beyond end of urosomite 1.

Antenna 1 ( Fig. 14 C) length ratio of peduncular articles 1–3 = 1.00: 0.52: 0.26, peduncular article 1 widest in middle, about 0.6 x as long as wide, distal half of ventral margin with long setular tufts; flagellum 7-articulate, shorter than peduncle, with slender aesthetascs ventrally.

Antenna 2 ( Fig. 14 D) elongate, slightly shorter than body length; peduncular articles 1–3 short, peduncular article 4 convex ventromedially, 1.60 x as long as article 5, with numerous setular tufts dorsally; flagellum slender, elongate, about 4 x as long as peduncle, more than 26-articulate.

Lower lip ( Fig. 14 E) inner lobes well developed, as long as outer; outer lobes subquadrate, apical margin flat, with fine pubescence.

Mandible ( Figs. 14 F–G) similar to each other, subtriangular; incisor broad, smooth and blunt; lacinia mobilis medium, left bidentate, right tridentate; molar prominent, well developed.

Maxilla 1 ( Fig. 14 H) inner plate small, lacking apical seta; outer plate with 7 tooth-like spines apically; palp biarticulate, distal article slightly shorter than proximal, with 2 simple setae apically and slender acute tooth.

Maxilla 2 ( Fig. 14 I) inner plate medium, apical margin with 3 setae; outer plate about twice length of inner one, with 1 seta laterally and 6 setae apically.

Maxilliped ( Fig. 14 J) inner plate very small, with 2 unequal setae apically; outer plate large, broad, not reaching end of palp article 2, medial margin with 7 setae and 4 spine-teeth distally; palp 4-articulate, medial margins with fine setae; article 2 elongate, 1.29 x as long as article 1, 2.30 x as long as article 3; article 4 0.45 x as long as article 3, with long claw apically.

Gnathopod 1 ( Fig. 14 K) coxa slender, elongate-ovate, with 1 long seta and 2 short setules apically; basis elongate, 1.22 x as long as carpus and propodus combined, curved and narrowing proximally, with 2 setae anteriorly, 1 long seta posterodistally; ischium 0.66 x as long as merus, with 1 posterodistal seta; merus with 6 simple setae posterodistally; carpus widening distally, 1.66 x as long as merus, anterior margin with 2 strong setae, with 4 simple, 3 pinnate setae ventrally; propodus subequal in length to carpus, anterior margin about twice length of posterior; palm oblique, with fine unequal setules marginally, defined by 4 spines on palmar corner; dactylus falcate, about half length of propodus, with distinct tooth on inner margin.

Gnathopod 2 ( Fig. 15 A) similar to gnathopod 1, but basis proximally straight not curved, carpus and propodus thin, narrower and longer than those of gnathopod 1; carpus 1.39 x as long as propodus.

Pereopod 3 ( Fig. 15 B) coxa subquadrate, with rounded corners, ventral margin with 4 setae; basis rectangular, subequal in length to merus–carpus combined, anterior margin with 7 long setae; merus 1.56 x as long as carpus, with long setae on both margins; carpus slightly shorter than propodus, with 6 long setae ventrally; propodus 1.46 x as long as dactylus.

Pereopod 4 similar to pereopod 3.

Pereopod 5 ( Fig. 15 C) coxa bilobate, posterodistal lobe large, round, broadly expanded ventrally; basis subovate, somewhat pear-shaped, gradually narrowing proximally, 0.75 x as wide as long, anterior margin curved, with row of 17 short pinnate setae, posterior margin straight, with 6 fine setules; merus 1.15 x as long as and about 2.5 x as wide as carpus, with 4 pinnate setae anteriorly, 4 short pinnate setae posteriorly and 1 spine posterodistally; carpus slender, subequal in length to propodus, with 2 posteromedial and 2 posterodistal spines; dactylus falcate, about half length of propodus.

Pereopod 6 ( Fig. 15 D) coxa subovate, weakly bilobate, anterior lobe small, posterior lobe large, with 1 ventral setule; basis anterior margin straight, proximoposterior margin broadly expanded, narrowing strongly distally, proximal width about 2.9 x as wide as distal; merus 1.13 x as long as carpus, with pinnate setae on both margins; propodus 1.07 x as long as carpus, with 3 anteromedial setae; dactylus slender, long, 0.68 x as long as propodus.

Pereopod 7 ( Fig. 15 E) coxa semicircular, ventral margin broadly convex; basis anterior margin straight, greatly expanded posteriorly, 0.81 x as wide as long; merus comparatively thick, 0.57 x as wide as long, with rows of pinnate setae on both margins, spines on anterior margin, 1 spine posterodistally; carpus as long as propodus, with rows of pinnate setae, small spines on anterior margin, pinnate setae posteriorly, long slender spine posterodistally; dactylus about half length of propodus.

Uropod 1 ( Fig. 15 F) peduncle 1.61 x as long as outer ramus, with 2 dorsolateral, 2 dorsomedial, 2 basofacial and 1 apicomedial spine; outer ramus slightly longer than inner, with 2 apical spines of unequal length; inner ramus with 1 long spine apically.

Uropod 2 ( Fig. 15 G) peduncle 1.49 x as long as outer ramus, with 4 dorsolateral and 1 apicomedial spine; outer ramus slightly longer than inner, both with long spines apically.

Uropod 3 ( Fig. 15 H) peduncle stout, slightly longer than outer ramus, slightly shorter than inner one, with 1 distal spine; inner ramus longer than outer, with row of long pinnate setae.

Telson ( Fig. 15 I) gradually rounded and slightly narrowing distally, length about 1.4 x width, deeply cleft (89%), lobes with long pinnate or penicillate setae apically and subapically.

Distribution. Japan (Kyushu), Korea (west and south coasts).

Remarks. The shape of the dorsal process of urosomite 1 is a unique and characteristic feature for the genus Guernea . Our specimens are in good agreement with the original description of Hirayama (1985), as it pertains to urosomite 1. However several morphological differences are found between our specimens and Hirayama’s: 1) maxilla 1 palp biarticulate (nonarticulated in original description); 2) maxilla 2 inner lobe with 3 apical setae (2 setae in original description); 3) uropod 3 peduncle slightly longer than outer ramus, slightly shorter than inner one (peduncle shorter than rami in original description); 4) uropod 3 inner ramus slightly longer than outer (both rami equal in length in original description). These slight differences (except the biarticulate palp) are deemed insufficient to warrant the erection of a new species for our material at this time, especially as we have not examined Hirayama’s type material for the condition of the maxilla 1 palp.

Figures

FIGURE 14. Guernea nullispina Hirayama, 1985, male, 2.7 mm, Anpo, Yeosu-si, Korea: A, habitus, lateral; B, pleonites and urosomites; C, antenna 1; D, antenna 2; E, lower lip; F, left mandible; G, right mandible; H, maxilla 1; I, maxilla 2; J, maxilliped; K, gnathopod 1. Scale bars = 0.2 mm (A – B), 0.1 mm (C – D, K), 0.05 mm (E – J).

FIGURE 15. Guernea nullispina Hirayama, 1985, male, 2.7 mm, Anpo, Yeosu-si, Korea: A, gnathopod 2; B, pereopod 3; C, pereopod 5; D, pereopod 6; E, pereopod 7; F, uropod 1; G, uropod 2; H, uropod 3; I, telson. Scale bars = 0.1 mm (A – H), 0.05 mm (I).

FIGURE 2. A, Guernea ezoensis; B, G. jejuensis sp. nov.; C, G. namhaensis sp. nov.; D, G. nullispina. Scale bars = 0.5 mm.