Diplocirrus tohokuensis, Jimi & Fujiwara & Kajihara, 2017

Jimi, Naoto, Fujiwara, Yoshihiro & Kajihara, Hiroshi, 2017, Remarkable biodiversity of flabelligerids in Japan: seven new species of Diplocirrus (Annelida: Flabelligeridae) from Japanese waters, Zootaxa 4337 (3) : -

Diplocirrus tohokuensis sp. nov.

(New Japanese name: Tohoku-konbou-habouki) ( Figure 6 )

Type materials. Holotype: NSMT-Pol H-643, off Otsuchi St. 1, 225 m depth, collected by NJ, COI sequence could not be determined . Paratype: NSMT-Pol P-644, off Ohakozaki , 99–102 m depth, one incomplete specimen (13 mm long, 1 mm wide, 35 chaetigers).

Description. Holotype complete, 21 mm long, 1.2 mm wide (in chaetiger 10), 43 chaetigers. Body with first 15 chaetigers swollen, thereafter cylindrical ( Fig. 6A ). Tunic whitish in ethanol with sediment particles on body wall and papillae ( Fig. 6B ); particles present on whole body wall except cephalic hood. Digitate papillae abundant, longer than wide, short, in median chaetigers about 1/20 as long as notochaetae and 1/4 as long as lateral papillae in chaetal lobe, arranged in 5–7 transverse rows per segment. Cephalic hood transparent, without papillae. Gonopodial lobe and gonopores absent. Posterior region tapered, anus without cirri.

Two types of branchiae present: dorsal branchiae 0.5 mm long, thick, with one lobe on internal side, not lamellate ( Fig. 6C ); ventral branchiae 1.7 mm long, thin, smooth, not lamellate ( Fig. 6D ). Palps 0.7 mm long, grooved. Upper and lateral lips well developed. Caruncle poorly developed, not separating dorsal branchiae ( Fig. 6E ). Eyes absent. Nephridial lobes present on branchial plate, whitish.

Parapodia poorly developed, chaetae emerging from body wall; notopodia with 1 lateral papilla on anterior side and 3–5 lateral papillae on posterior side; neuropodia with 1–2 lateral papillae on anterior side and 1–2 lateral papillae on posterior side. Cephalic cage poorly developed (1 st notochaeta 0.4 mm long). Notochaetae 5–7 per bundle, multiarticulate ( Fig. 6F ) with 43–46 articles in chaetiger 27; tip tapered. Neurochaetae 4–6 per bundle, multiarticulate ( Fig. 6G ) with 17–21 articles in chaetiger 27, rounded projection poorly developed; subdistal article 2 times longer than wide; tip slightly falcate.

Distribution. Off Tohoku, Japan; 99–225 m depth.

Etymology. The specific name is an adjective, after the type locality (Tohoku).

Remarks. Diplocirrus tohokuensis sp. nov. resembles D. glaucus ( Malmgren, 1867) and D. toyoshioae sp. nov. in the following features: i) body papillae are short and abundant, ii) body is covered with sediment particles, iii) anterior chaetigers are swollen, and iv) gonopores are absent. These three species can be discriminated by i) cephalic cage, ii) neurochaeta, and iii) color of the anterior chaetigers. The cephalic cage in D. tohokuensis sp. nov. is not well developed (1/3 as long as body width), whereas in D. glaucus and D. toyoshioae sp. nov. are longer (as long as body width). The neurochaetal round projection is poorly developed in each article of D. tohokuensis sp. nov. and D. glaucus , whereas they are well developed in D. toyoshioae sp. nov. The anterior chaetigers of D. tohokuensis sp. nov. and D. toyoshioae sp. nov. are whitish, whereas these possess rusty pigments in D. glaucus .

Figures

FIGURE 6. Diplocirrus tohokuensis sp. nov. Holotype (NSMT-Pol H- 643). A, anterior end, ventral view. B, body wall, ventral view. C, dorsal branchia. D, ventral branchia. E, prostomium, F, notochaetae, chaetiger 27. G, neurochaetae, chaetiger 27 (insert: chaetal tip). Abbreviations: BS, branchial scar; Ca, caruncle; LL, lateral lip; NL, nephridial lobe; PS, palp scar. Scale bars: A, 5 mm; B – E, 500 µm; F – G, 100 µm; G (insert), 20 µm.