Polydora sp. 3 Fig. 8N-P

Larval morphology.

Overall body shape slender. Prostomium broad and rounded anteriorly. Three pairs of black eyes present; median pair of eyes rounded, most lateral pairs double-eyes, ramified melanophore between innermost and next to innermost pairs of eyes present. Large patches of black pigment located on lateral part of peristomium, behind prototroch. Dorsal pigment pattern consists of two rows of melanophores from chaetiger III with those of first four or five chaetigers being band-shaped and then replaced by ramified branching melanophores (Fig. 8O). These melanophores undergo expansion and contraction. Lateral pigment found on chaetigers II-IV, resumes again from chaetiger VII in late larvae (Fig. 8P). A pair of black pigment patches occur on pygidium. Ventral brown and black pigment present on posterior part in late larvae ready to metamorphose. Pygidium has a dorsal notch and lacks appendages. Telotroch well developed. Gastrotrochs on chaetigers III, V, VII, IX, X, XIII, XV, and XVII, lost on chaetigers III and V in late larvae (Fig. 8P). In late larvae, modified chaetae develop in chaetiger V.

Remarks.

No benthic adult stages were collected in the present study. The 18S rRNA gene sequences obtained from the larvae did not match any available Polydora sequences. As the larvae formed a robustly supported monophyletic clade with other Polydora species (Figs 2, 3), this species was referred to Polydora sp. 3.

Planktonic larvae of this species were collected from December to June in Onagawa Bay every year during the study period. Planktonic larvae of this species were previously reported to be abundant in Onagawa Bay in the winter season from December to March (Abe et al. 2014, as Polydora sp.). Large patches of black pigment on the lateral peristomium are the main characteristic of this species and differentiate it from the other species of the genus observed in the present study, even at early planktonic stages (Fig. 8N).