SYSTEMATICS
Family Flabelligeridae de Saint-Joseph, 1894
Genus Diplocirrus Haase, 1915
(New Japanese name: Konbouhabouki-zoku)
Diplocirrus nicolaji (Buzhinskaja, 1994)
(New Japanese name: Bouzu-habouki)
(Figs. 2, 3)
Diversibranchius nicolaji Buzhinskaya, 1994: 231, figures 2–7; Darbyshire and Mackie 2009: 97, Table 1.
Flabelligeridae from Japan: Rouse and Pleijel 2001, plate 11, figure f.
Diplocirrus nicolaji: Salazar-Vallejo and Buzhinskaja 2011, 31–33 figure 9.
Material examined
Oshoro: NSMT-Pol-113032, One of unknown sex, Body length 36.2 mm, Body width 1.9 mm, 49 chaetigers, 20 October 2014, coll. N. Jimi, 2 m depth, gravelly sand.
Tateyama: NSMT-Pol-113033, One of unknown sex (anterior fragment), Body length 16.0 mm, Body width 3.0 mm, 19 chaetigers, 6 March 2015, coll. M. Tanaka, 4–10 m depth, sand.
Misaki: NSMT-Pol-113034, 113036, 12 of unknown sex (one complete specimen and 11 anterior fragments), Body length 8.0–18.6 mm, Body width 1.8 mm, 29 chaetigers, 16 October 2014, coll. N. Jimi, 4 m depth, sand.
Komatsubara: NSMT-Pol-113035, Six of unknown sex (two complete specimens and four anterior fragments), Body length 17.0–26.2 mm, Body width 1.2–1.7 mm, 31–51 chaetigers, 2 September 2014, coll. N. Jimi, 2 m depth, sandy mud.
Description
Body length 8.0–36.2 mm and width 1.2–1.9 mm, chaetigers 29–51, and orange yellow in colour. Anterior and last few segments slightly swollen. Cephalic cage absent (1st chaetiger notochaeta 0.2–0.5 mm). Tunic densely covered by digitate or bowling-pin shaped papillae which arranging as 10–17 rows per segment (Fig. 2a). Cephalic hood white colour and thinly covered by papillae. Eyes absent (Fig. 3a). One pair of palps, which 0.8–8.3 mm long, grooved. Lobes reduced and rounded. Two types of branchiae present, green colour when alive, but faded to white in ethanol preserved specimens (Fig. 3b, c). Four branchiae in posterior row; 0.5–1.4 mm long and lamellate. Lamella reaching tips, lamellate surface ciliated, and two sucker-like sockets on lateral side (Fig. 3d). Four branchiae in anterior row; 0.7–1.9 mm long and lamellate. Lamella reaching to one-third of its branchial length. Branchial surface ciliated (Figs. 2b, 3e). Chaetiger 1 notosetae emerging from dorsal side contrary to following setigers. Chaetigers 3 to 8 or 9 swollen, without clear segmentation of tunic between them. Gonopores orange red, present in chaetigers 2 to 23–48 (Fig. 3f). Parapodia poorly developed. Chaetae emerging directly from body wall. Notochaeta and neurochaeta multiarticulated, 5–7 per bundles (Fig. 2a); 23–26 articles on notochaeta and 9–11 articles on neurochaeta in median chaetigers.
Variation among four localities
The palp length of the specimen from Oshoro was much longer than that of specimens from the other localities (Fig. 3c). The preserved branchial colour of the specimens from Misaki was often green as in its live state, but the colour of the specimens from other localities are soon faded to white.
Phylogenetic analysis
The final length of the aligned COXI sequence was 531 bp; this contained 230 variable sites, of which 213 sites were parsimony informative. The mean base composition was 28.3 % (A), 20.2 % (C), 16.4 % (G), and 35 % (T).
The ML tree obtained (Fig. 4) showed that the monophyly of Flabelligeridae was strongly supported (bootstrap [BS] value = 95 %); however, the internal relationships within the family were totally unresolved. All the sequences of Diplocirrus nicolaji formed a monophyletic clade with high support value (BS value = 94 %) and were well discriminated from the remains (Fig. 4). The average genetic divergence of the sequences among D. nicolaji was 2.1 ± 1.6 % in p-distance (2.2 ± 2 % in K2P). Monophyly of the two Diplocirrus species included, D. longisetosus and D. nicolaji, was not supported.