Eudorella acuticaudata Akiyama & Gamô, 2012, sp. nov.

Eudorella acuticaudata sp. nov.

(Figs. 1–3)

Eudorella sp. Akiyama 2009: 487.

Material examined. Holotype, ovigerous female, 4.2 mm (dissected) (NSMT-Cr 22093), off Abashiri, southern Okhotsk Sea, 44°07ˏN, 144°, 34ˏE – 44°06ˏN, 144°34ˏ E, 305–309 m (KT-01-14, St. AB-5), 20 September, 2001. Paratypes: 2 ovigerous females, 4.2 mm (dissected) (NSMT-Cr 22094), off Abashiri (KT-01-14, St. AB-5); 2 adult males, 4.3, 6.5 mm (dissected) (NSMT-Cr 22095), 8 preparatory females, 4.2–6.7 mm (dissected) (NSMT-Cr 22096), off Abashiri, Hokkaido, Okhotsk Sea, 44°06ˏN, 144°42ˏE–44°06ˏN, 144°43ˏE, 313–335 m (KT-04-20, St. AB-3), 12 September, 2004.

Description. Ovigerous females (Figs.1, 2). The 11 specimens examined were classified into two size groups: 4.2–4.6 mm in length (6 specimens), and 5.7–6.7 mm in length (5 specimens). Data for the larger group are presented within parentheses.

Body weakly calcified, with few setae (Fig. 1 A, B). Length of carapace 0.18–0.19 (0.19–0.20) times total body length, 1.0–1.1 (1.1–1.2) times carapace width, and 1.0–1.1(1.0–1.1) times carapace depth; upper front corner vaulted, with a bundle of short setae projecting upward; anterior margin not serrated; antennal notch (arrowheads in Fig. 1 C, D) with 0–3 (0–4) minute teeth on upper end and 2–3 (3–4) prominent teeth on lower end; inferior margin with 6–9 (10–17) teeth, foremost one large, directed forward. Pereon length 1.3–1.5 (1.3–1.5) times carapace length. Pleon length 0.53–0.55 (0.53–0.54) times total body length; dorso-posterior end of pleonite 5 without long setae; middle portion of posterior end of pleonite 6 pointed.

Antenna 1 (Fig. 1 E) robust; 1st article of peduncle with 2–3 (2–3) and 3 (2–4) plumose setae on lower and inner margin; 3rd article of peduncle swollen at distal portion, shorter than 2nd, with 3 (3–6) plumose and 1 simple setae on outer margin, 4 (4–6) plumose setae on inner margin, and 1 simple seta on frontal margin. Main flagellum as long as 2nd article of peduncle, with 1 (1) simple seta on outer margin of 1st article; accessory flagellum, thickened distally, slightly longer than 1st article of main flagellum. Antenna 2 (Fig. 1 F) with no plumose setae on lower margin. Mandibles (Fig. 1 G) broad and truncated at base; 2 thin setae between molar process and pars incisiva; right mandible with small spiniform seta, located on the same locus as lacinia moils on right mandibles. Maxilla 1 (Fig. 1 H), outer endite with 9 stout setae, inner endite with 4 setae; palp with 1 long filament. Maxilla 2 (Fig. 1 I): 2 narrow endites with 3 and 4 stout setae; lower half of protopod with thick plumose setae. Maxilliped 1 (Fig. 1 J) with 5–6 (7–9) branchial lobules. Maxilliped 2 (Fig. 1 K) basis longer than combined length of succeeding 3 articles, with 1 short simple seta on inner margin of basal region; carpus with about 10 setae on inner margin. Maxilliped 3 (Fig. 1 L) basis 1.2–1.3 (1.3–1.5) times distal articles combined, with 8–11 (8–12) and 6–9 (7–12) plumose setae on inner and ventral surface; ischium without spine on inner margin; carpus with 5 (5) plumose setae on inner margin.

Pereopod 1 (Fig. 1 M) basis length 0.8 (0.9–1.0) times distal articles combined, with 8–11 (15–22) and 8–10 (9–13) plumose setae on inner and outer margin; propodus 1.3–1.4 (1.3–1.5) times carpus; dactylus 0.5–0.6 (0.5) times propodus. Pereopod 2 (Fig. 2 A) basis 0.8–0.9 (0.8–1.0) times distal articles combined, with 10–16 (10–19) plumose setae on inner margin; carpus 0.9–1.1 (1.0–1.3) times merus; propodus short, with very shallow notch on distal corner; dactylus with 9–10 (11–13) stiff setae. Pereopod 3 (Fig. 2 B) basis 1.9–2.1 (2.0–2.3) times distal articles combined. Pereopod 4 (Fig. 2 C) basis 1.2–1.6 (1.5–1.7) times distal articles combined. Pereopod 5 (Fig. 2 D) basis 0.9–1.1 (1.0–1.4) times distal articles combined.

Uropod (Fig. 2 E) robust. Peduncle length 1.2–1.3 (1.3) times as long as pleonite 6, 1.18–1.28 (1.09–1.22) times exopod, 0.83–0.96 (0.90–1.03) times endopod, with 5–9 (6–11) robust setae on inner margin. Exopod 1.07– 1.18 (1.10–1.16) times 1st article of endopod, with 7–8 (8–10) setae on inner margin and 3–5 (5–6) simple setae on dorsal surface. Endopod 1st article 2.4–2.9 (2.5–3.0) times 2nd article, with 8–9 (9–12) spiniform setae on inner margin and 3–4 (4–6) setae on inner and outer margin; 2nd article with 4 and spiniform setae on inner margin; terminal robust seta defined at base.

Adult males 4.3 mm and 6.5 mm in length (Fig. 3). Data for larger specimen presented in parentheses. Body covered with sparse short hairs. Carapace 0.22 (0.20) times total body length, 1.3 (1.3) times greatest width, width subequal to depth (Fig. 3 A, B); upper front corner round, antennal notch obsolete; frontal margin not serrated; antero-lateral corner with a tooth projecting forward (Fig. 3 C). Pereon 1.20 (1.35) times carapace. Pleon 0.53 (0.53) times total body length, with 2 pairs of pleopods; dorso-posterior end of 5th pleonite with no long seta; hind margin of pleonite 6 triangular in shape, pointed at middle portion.

Antenna 1 (Fig. 3 D) robust; 3rd article of peduncle much shorter than 2nd, with 3 (3) plumose and 1 (2) simple setae on outer surface, 4 (4–5) plumose setae on inner, and 1 simple seta on frontal margin. 4-articulate main flagellum shorter than 2nd joint of peduncle and much longer than 3rd, with 1 (1) simple seta on outer margin of 2nd article; frontal margin of basal article with 6 (6) aesthetascs. Accessory flagellum longer than combined length of 1st and 2nd articles of main flagellum. Antenna 2 (Fig. 3 E) with 4 plumose setae on basal articles; flagellum reaching near posterior end of pleon. Maxilliped 3 (Fig. 3 F) basis length 1.6 (1.7) times distal articles combined, with 7 (11) and 5 (11) plumose setae on inner margin and ventral surface.

Pereopod 1 (Fig. 3 G) basis 1.0 (1.1) times distal articles combined, with 8 (17) and 8 (15) plumose setae on inner and outer margin; propodus 1.3 (1.3) times merus; dactylus 0.6 (0.5) times propodus. Pereopod 2 (Fig. 3 H) basis 1.4 (1.3) times distal articles combined, with 11 (22) plumose setae on inner margin; carpus as long as merus; dactylus slightly swollen, with 8 (11–12) stiff simple setae, more than twice as propodus length. Pereopods 3–5 (Fig. 3 I–K) bases 3.8 (3.0), 2.6 (2.6), 1.6 (1.6) times distal articles combined, respectively. Pleopod 1 (Fig. 3 L) normal.

Uropod (Fig. 3 M) peduncle 1.2 (1.3) times as long as pleonite 6, 1.00 (1.00) times exopod, 0 79 (0.83) times endopod, with 6 (10) short and 5 (7) long setae on inner margin. Exopod 1.07 (1.12) times 1st article of endopod, with 7 (8) and 4 (4) setae on inner margin and dorsal surface, respectively. Endopod 1st article, 2.7 (2.8) times 2nd, with 12 (17) spiniform setae and 6 (7) long setae on inner margin, 3 (7) setae on outer margin; 2nd article with 5 (5) spiniform setae and 1 simple setae on inner and outer margin, respectively; a long terminal seta present at apex.

Etymology. The species name refers to the pointed posterior end of pleonite 6 (Fig. 2 E).

Remarks. The present new species is distinguished from the other species in the genus by the pointed posterior end of pleonite 6 in both females and males (Figs. 2 E, 3M). Eudorella acuticaudata sp. nov. resembles E. pusilla Sars, 1871, from the Atlantic coast of North America in their vaulted pseudorostral lobes of the carapace. These two species also resemble each other in the strongly constructed antenna 1 with the 3rd peduncular article widened apically; main flagellum having only one seta on the outer margin. However, the new species is distinguished from E. pusilla in the following: (1) the uropod exopod is longer than the endopod 1st article (shorter than the endopod 1st article in E. pusilla); (2) the uropod endopod 1st article is less than three times longer than the 2nd article (4 times in E. pusilla); and (3) the pointed last pleonite (not pointed in E. pusilla), and (4) uropod endopod terminal seta articuleted (fused in E. pusilla). The morphological characteristics of the large-sized group of specimens agree with those of the small-sized group, except that the appendages are more setiferous in the new species. Two adult males, sorted from the same sediment sample (KT-04-20, St. AB-3), were placed into the smaller and larger size groups.

Distribution. Northern coast of Hokkaido, Okhotsk Sea, Pacific coast of northern Honshu, 249– 335 m.