Diplocirrus mamoi Jimi & Fujiwara & Kajihara 2017, sp. nov.

Diplocirrus mamoi sp. nov.

(New Japanese name: Mamo-konbou-habouki) (Figure 3)

Type materials. Holotype: NSMT-Pol H-636, off Moroiso, 77–78 m depth, collected by Mr. Hisanori Kohtsuka, COI sequence DDBJ accession no. LC314564. Paratypes: NSMT-Pol P-637, off Moroiso, 77–78 m depth, collected by Mr. Hisanori Kohtsuka, eight incomplete specimens (11–26 mm long, 1.0– 1.5 mm wide, 15–43 chaetigers).

Description. Holotype incomplete, 16 mm long, 1.5 mm wide (in chaetiger 10), 28 chaetigers. Body with first 16 chaetigers swollen, thereafter cylindrical (Fig. 3A). Tunic whitish in ethanol with sediment particles only on base of papillae (Fig. 3B). Digitate papillae abundant, longer than wide, short, in median chaetigers about 1/7 as long as notochaetae and as long as lateral papillae in chaetal lobe, arranged in 11–13 transverse rows per segment. Cephalic hood transparent, with papillae near 1 st chaetiger. Gonopodial lobes not seen. Gonopores present in chaetigers 3–13, pale brown (Fig. 3B). Posterior region tapered, anal part lost in holotype.

Two types of branchiae present: dorsal branchiae 1 mm long, thick, with one lobe in internal side, not lamellate (Fig. 3C); ventral branchiae 1 mm long, thin, smooth, not lamellate (Fig. 3D). Palps 2 mm long, grooved. Upper and lateral lips well developed. Caruncle projected, not separating dorsal branchiae (Fig. 3E). Eyes absent. Nephridial lobes present.

Parapodia poorly developed, chaetae emerge from body wall; lateral papillae in chaetal lobes as long as other body papillae. Cephalic cage poorly developed (1 st notochaeta 0.3 mm). Notochaetae 4–6 per bundle, multiarticulate (Fig. 3F) with 17–21 articles in chaetiger 28; tip tapered. Neurochaetae 2–3 per bundle, multiarticulate (Fig. 3G) with 5–6 articles in chaetiger 28, rounded projection poorly developed; subdistal article 8–9 times longer than wide; tip falcate.

Distribution. Only known from type locality (off Moroiso); 77–78 m depth.

Etymology. The species is named after Mr. Mamoru Sekifuji, the Captain of the research boat Rinkai-maru at Misaki Marine Biological Station, who helped during the collection of the type specimens and contributed to elucidate the invertebrate fauna in Sagami Bay. The specific name is a noun in the genitive case.

Remarks. Diplocirrus mamoi sp. nov. resembles D. nicolaji and D. asamushiensis sp. nov. in the following features: i) body papillae are abundant and short, ii) sediment particles are attached only on the base of papillae, iii) cephalic cage is poorly developed, and iv) neurochaetal articles are less than 22 in median chaetigers. These three species are discriminated by the three features: branchial forms, caruncle length and number of neurochaetal articles. Both of the two types of branchiae in D. mamoi sp. nov. and D. asamushiensis sp. nov. are smooth, whereas they are lamellate in D. nicolaji. The dorsal branchiae of D. mamoi are as long as ventral ones, whereas they are shorter than the ventral ones in D. asamushiensis sp. nov. The number of the median neurochaetal articles in D. mamoi sp. nov. ranges from five to six, whereas it is 7–9 in D. asamushiensis sp. nov. Subdistal article of D. mamoi sp. nov. is 8–9 times longer than wide, whereas it in D. asamushiensis sp. nov. is 5–6 times longer than wide.