Diplocirrus imajimai, 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 imajimai sp. nov.

(New Japanese name: Imajima-konbou-habouki) ( Figure 2 )

Type material. Holotype: NSMT-Pol H-635, off Otsuchi St. 2, 215 m depth, collected by NJ, COI sequence could not be determined.

Description. Holotype incomplete, 11 mm long, 1 mm wide (in chaetiger 10), 18 chaetigers. Body with first 9 chaetigers swollen, thereafter cylindrical ( Fig. 2A ). Tunic whitish in ethanol without sediment particles ( Fig. 2B ). Digitate papillae abundant, longer than wide, short, in median chaetigers about 1/25 as long as notochaetae and 1/4 as long as lateral papillae in chaetal lobe, arranged in 4–5 transverse rows per segment. Cephalic hood transparent, without papillae. Gonopodial lobe and gonopores absent. Posterior region tapered; anal part lost in holotype.

Two types of branchiae present: dorsal branchiae 0.8 mm long, thick, with one lobe in internal side, not lamellate ( Fig. 2C ); ventral branchiae 0.9 mm long, thick, smooth, not lamellate ( Fig. 2D ). Palps 1.0 mm long, grooved. Upper and lateral lips well developed. Caruncle poorly projected, not separating dorsal branchiae. Eyes absent. Nephridial lobes present, whitish ( Fig. 2E ).

Parapodia poorly developed, chaetae emerging from body wall; notopodia with no lateral papillae on anterior side and 1–3 lateral papillae on posterior side; neuropodia with no lateral papillae on anterior side and 1–2 lateral papillae on posterior side. Cephalic cage developed (1 st notochaeta 1.2 mm in length). Notochaetae 5–8 per bundle, multiarticulate ( Fig. 2F ) with 15–19 articles in chaetiger 19; tip capillary. Neurochaetae 4–6 per bundle, multiarticulate ( Fig. 2G ) with 12–15 articles in chaetiger 19, rounded projection poorly developed; subdistal article 3–4 times longer than wide; tip slightly falcate.

Distribution. Only known from type locality, off Otsuchi, 215 m depth.

Etymology. This species is named after Dr. Minoru Imajima in recognition of his great taxonomic works about Japanese polychaetes. The specific name is a noun in the genitive case.

Remarks. Diplocirrus imajimai sp. nov. resembles D. capensis Day, 1961 in the following features: i) body papillae are short, longer than wide, and abundant, ii) body is not covered with sediment particles, and iii) gonopores are absent. The cephalic cage of D. imajimai sp. nov. is well developed (longer than body wide), whereas it is poorly developed in D. capensis (chaetiger 1 shorter than following ones). Diplocirrus capensis has black eyes, whereas D. imajimai sp. nov. does not have eyes.

Figures

FIGURE 2. Diplocirrus imajimai sp. nov. Holotype (NSMT-Pol H- 635). A, anterior end, lateral view. B, body wall, ventral view. C, dorsal branchia. D, ventral branchia. E, prostomium. F, notochaetae, chaetiger 19. G, neurochaetae, chaetiger 19 (insert: chaetal tip). Abbreviation: PS, palp scar. Scale bars: A, 2 mm; B – E, 500 µm; F – G, 100 µm; G (insert), 10 µm.