Eudorella emarginata ( Kröyer, 1846 ), Kroyer, 1846

Akiyama, Tadashi & Gamô, Sigeo, 2012, The cumacean Genus Eudorella (Crustacea: Peracarida) from Japanese Waters, Northwest Pacific, and E. suluensis sp. nov. from the Sulu Sea, Indo-West Pacific, Zootaxa 3319, pp. 1-56 : 27-30

Eudorella emarginata ( Kröyer, 1846)

( Figs. 18 , 19 )

Leucon emarginattus Kröyer, 1846: 181 , 209, 211, pl. 2, fig. 3a–h.

Eudorella emarginata Sars, 1900: 36 , pls. 27–28; Stebbing 1913, 75–77, Figs. 40–42; Jones 1976, 28, Fig9 E–H; Akiyama 2009: 486.

Material examined. 5 ovigerous females, 9.1–11.1 mm, 1 adult male, 9.7 mm, 3 subadult males, 9.0 mm, 8.8 mm (NSMT-Cr 22127), off Kushiro, Hokkaido, 42°28ˏN,144°15ˏE – 42°27ˏN, 144°13ˏE, 965–982 m (KH-01-2, St. XR-2), 15 September 2001; 1 ovigerous female, badly damaged, 2 preparatory females, 12.1 mm, 11.4 mm, 1 subadult male, 9.3 mm (NSMT-Cr 22128), 42°10ˏN, 144°10ˏE – 42°11ˏN, 144°12ˏE, 1134–1219 m (KH-01-2, St. KC0), 18 September, 2001 (NSMT-Cr 22129). 6 ovigerous females, 9.8–12.1 mm, 5 preparatory females, 10.6– 13.0 mm, 1 adult male (pleonite 6 and uropods lost), 3 subadult males, length 9.2 mm, 8.6 mm (NSMT-Cr 22130), off Todogasaki, northeast of Honshu, 39°31ˏN, 142°32ˏE – 39°32ˏN, 142°34ˏE, 1002–1069 m (KH-01-2, St. TD- 2), 25 September, 2001. 3 ovigerous females, 8.7–9.4mm, 3 adult males, length 8.9–9.5 mm (NSMT-Cr 22131), off Abashiri, Okhotsk Sea, 44°06ˏN, 144°42ˏE – 44°06ˏN, 144°43ˏE, 313–335 m (KT-04-20, St. AB-3), 12 September, 2004.

Description. 13 ovigerous and 7 preparatory females, 8.6–13.0 mm ( Fig. 18 ). Carapace length 0.18–0.20 times total body length, 1.1–1.2 times greatest width, latter being 1.1–1.2 times depth; frontal margin not serrated, except for a few specimens having very weakly serrated frontal margin; antennal notch and lower region forming large, somewhat triangular sinus; anterolateral angle with prominent tooth directed forward, succeeded by a series of teeth on inferior margin; pereon 1.2–1.5 times carapace. Pleon 0.53–0.60 times total animal length. Dorso-posterior end of pleonite 5 with 0 or 2 thin long setae.

Antenna 1 ( Fig. 18 C) 1st article of peduncle with 2–6 and 2–4 plumose setae on lower and inner margins respectively; 3rd article of peduncle subequal or shorter than 2nd, with 6–9 plumose setae and 1 simple seta on outer margin, with 6–9 plumose setae on inner margin, and with 3–6 plumose setae on frontal margin. Main flagellum longer than 2nd joint of peduncle; basal article with 4–7 simple setae on outer margin. Accessory flagellum shorter than 1st article of main flagellum. Antenna 2 ( Fig. 18 D) with 5–6 plumose setae on proximal region of peduncle; flagellum long, exceeding pleon. Mandibles, maxilla 1 and maxilla 2 normal ( Fig. 18 E–G). Maxilliped 1 with 11–14 branchial lobules ( Fig. 18 H). Maxilliped 2 ( Fig. 18 I) basis strongly constructed, subequal to combined length of succeeding 3 articles, with several plumose setae on distal end; inner proximal corner of basis with a row of spines or teeth in ovigerous females. Maxilliped 3 ( Fig. 18 J) basis length 1.2–1.4 times length of distal articles combined, 10–33 and 9–17 plumose setae on inner margin and ventral surface respectively; ischium without a spine on inner margin; carpus with 7–10 plumose setae on inner margin.

Pereopod 1 ( Fig. 18 K) basis length 0.6–0.9 times length of distal articles combined, with many plumose setae on inner and outer margins and with 1–2 robust spiniform setae on ventral surface; propodus 1.1–1.4 times carpus; dactylus 0.5–0.6 times propodus. Pereopod 2 ( Fig. 18 L) basis length 0.6–0.8 times length of distal articles combined; carpus subequal to merus; propodus with deep notch on distal corner, for nearly entire length of article; dactylus swollen distally, with 19–27 stiff setae on lateral margin and apical end. Pereopods 3–5 ( Fig. 18 M–O) basis length 1.6–2.0, 1.4–2.1 and 1.2–1.9 times lengths of distal articles together respectively.

Uropod ( Fig. 18 P) peduncle 1.4–1.6 times as long as pleonite 6, 1.06–1.31 times exopod, 0.82–1.09 times endopod, with 9–16 simple setae on inner margin; exopod 0.9–1.0 times 1st article of endopod, with 11–16 plumose setae on inner margin and apical end, and with 4–9 simple setae on dorsal surface. Endopod 1st article 3.8–5.3 times 2nd article, with 16–22 spiniform setae on inner margin and with 7–11 setae on outer margin; 2nd article with 3–6 spiniform setae on inner margin; terminal robust setae defined at base.

Adult males (5 specimens) 8.9–10.2 mm ( Fig. 19 ). Carapace length 0.20–0.22 times total body length; upper front corner with few bristles; lower portion of frontal margin smooth or with a few teeth ( Fig. 19 C–E); antennal notch absent; anterolateral angle with 1 or a few small teeth ( Fig. 19 C–E). Pereon length 1.2 times that of carapace. Ventral surface of pereonite 5 with a pair of penial lobes ( Fig. 19 M). Pleon 0.54–0.56 times total body length; posterior end of pleonite 6 slightly elongate, reaching opening of anus ( Fig. 19 O).

Antenna 1 ( Fig. 19 F), 3rd article of peduncle subequal to 2nd, with 5–7 plumose setae on outer margin, 7 plumose setae on inner margin, and 2–3 plumose or simple setae on frontal margin; main flagellum 4-articulate, with numerous aesthetascs on frontal margin of basal article. Accessory flagellum a little longer than basal article of main flagellum. Antenna 2 ( Fig. 19 G) with 4–5 plumose setae on peduncle. Maxilliped 3 ( Fig. 19 H) basis length 1.5–1.6 times length of distal articles combined, with 8–16 and 8–12 plumose setae on inner margin and ventral surface, respectively.

Pereopod 1 ( Fig. 19 I) basis length 0.85–1.0 times length of distal articles combined, with 15–21 and 8–21 plumose setae on inner and outer margins, respectively, and with 1–2 spiniform setae on ventral surface; propodus longer than merus; dactylus 0.5–0.6 times as carpus. Pereopod 2 ( Fig. 19 J) basis length 1.1–1.2 times that of distal articles combined; carpus 0.9–1.1 times length merus; dactylus 1.1–1.3 times carpus and 3.3–3.9 times propodus, with 20–22 stiff simple setae projecting radially. Pereopods 3–5 ( Fig. 19 K–M) basis lengths 2.2–3.0, 2.3–3.2, 1.5– 2.4 times combined distal articles, respectively. Pleopod 1 normal ( Fig. 19 N).

Uropod ( Fig. 19 O) peduncle length1.3–1.4 times length of pleonite 6, 1.0–1.1 times exopod, 0.80–0.89 times basal article of endopod, with 9–13 spiniform setae on upper inner margin and with 9–11 simple setae on lower inner margin. Exopod length 0.80–0.89 times length of 1st article of endopod, with 12–16 setae on inner margin and apical end, and with 7–11 setae on dorsal surface. Endopod basal article length 4.7–5.4 times that of 2nd article, with 24–33 spiniform setae and 5–11 setae on inner margin, and with 13–15 setae on outer margin; 2nd article with 6–8 small spiniform setae on inner margin; terminal setae minute, defined at base.

Remarks. The morphology of the specimens examined in the present study agree with the description of Eudorella emarginata ( Kröyer, 1846) from the Atlantic region ( Sars 1900; Jones 1976). This species and five species of congeners, E. fallax Zimmer, 1909 , E. gracilior Zimmer, 1907 , E. groenlandica Zimmer, 1926 , E. minor Lomakina, 1952 , and E. spitzbergensis Zimmer, 1926 , are characterized by a large sinus on the frontal margin of the carapace. Eudorella emarginata is distinguished from the others in that the accessory flagellum of antenna 1 is much shorter than the 1st article of the main flagellum.

Noteworthy characters of the Japanese specimens are that: (1) antenna 2 has two plumose setae on its lower margin; (2) the basis of maxilliped 2 of ovigerous females has some teeth or spines at the inner proximal corner, and several plumose setae on the distal end; and (3) the basis of the pereopod 1 has one or two robust spiniform setae on the ventral surface.

Previous studies have reported very wide, circumpolar distribution of this species ( Bäcescu 1988) which possibly consists of local populations each with minor morphological variations. Some characters of the Japanese specimens do not agree with those of Atlantic specimens. (1) large sinus on the frontal margin of the carapace occasionally bears small teeth on the bottom, which is similar to E. groenlandica . (2) In Japanese ovigerous females (N = 13), pereonites 2 and 3 are characterized by relatively narrow, undeveloped side plates. Although the length of the carapace (L 1 in Fig. 19 A) found to be 2.66–3.38 times as long as the width of the side plate of pereonite 2 (L 2 in Fig. 19 A), the ratio is about 2 in Atlantic specimens, based on the illustrations by Sars (1900) and Jones (1976). (3) These were 11–14 branchial lobules on maxilliped 1 of the Japanese specimens were 11–14 (19 females, 8.6–13.0 mm in total body length), while there are only seven in those of the Atlantic specimen illustrated by Sars (1900), which had a total body length of 12 mm. Although these characters possibly represent local variations in their morphology, it is possible that the Japanese specimens belong to another, undescribed species.

Distribution. Atlantic boreal region, Arctic region, eastern Russia, northern Japan, Alaska, Canada, 0–2000 m.

Figures

FIGURE 9. Eudorella bathyalis Vassilenko and Tzareva, 2004, adult male. A, body, lateral view; B, anterior portion of body, from above; C, frontal margin of carapace; D, antenna 1; E, antenna 2; F, maxillipeds 3; G – K, pereopods 1 – 5; L, pleopod 1; M, urood with pleonite 6.

FIGURE 18. Eudorella emarginata (Kröyer, 1846), ovigerous female. A – D, female specimens; A, carapace and pereonite 1 – 5, lateral view; B, lower frontal margin of carapace; C, D, antenna 1 and 2; E, mandibles; F, maxilla 1; G, maxilla 2; H – J. maxillipeds 1 – 3; K – O, pereopods 1 – 5; P, uropod with pleonite 6.

FIGURE 19. Eudorella emarginata (Kröyer, 1846), adult male. A, body, lateral view; B, anterior portion of body, from above; C – E, lower frontal margin of carapace; F, antenna 1; G, antenna 2; H, maxilliped 3; I – L, pereopods 1 – 4, M, pereopod 5 and penial lobe; N, pleopod 1; O, uropod with pleonite 6.