Polydora sp. 3

Abe, Hirokazu & Sato-Okoshi, Waka, 2021, Molecular identification and larval morphology of spionid polychaetes (Annelida, Spionidae) from northeastern Japan, ZooKeys 1015, pp. 1-86 : 1

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 ).

Figures

Figure 2. Maximum Likelihood tree inferred from nuclear 18 S and mitochondrial 16 S rRNA gene sequences of spionids obtained from Japan in the present and previous studies (provided in Table 1). The gene sequences of adult and larval spionid polychaetes are indicated by solid squares and circles in front of each species name, respectively. SH-aLRT / approximate Bayes support / ultrafast bootstrap support values of ≥ 80 %, ≥ 0.95, ≥ 95 %, respectively are given beside the respective nodes. Nodes with red circles indicate triple high support values of SH-aLRT ≥ 80, approximate Bayes support ≥ 0.95, and ultrafast bootstrap support ≥ 95. The scale bar represents the number of substitutions per site. Sequences of Laonome sp. and Sabella pavonina Savigny, 1822 obtained from DDBJ / EMBL / GenBank were used for outgroup rooting.

Figure 3. Maximum Likelihood tree inferred from nuclear 18 S and mitochondrial 16 S rRNA gene sequences of spionid polychaetes obtained from Japan in the present and previous studies (shown in Table 1) and from DDBJ / EMBL / GenBank (shown in Table 2). The tree is divided into two parts A, B. The gene sequences obtained in the present study are highlighted by bold and red color and the adult and larval sequences are indicated by solid squares and circles in front of each species name, respectively. SH-aLRT / approximate Bayes support / ultrafast bootstrap support values of ≥ 80 % / ≥ 0.95 / ≥ 95 %, respectively are given beside the respective nodes. Nodes with red circles indicate triple high support values of SH-aLRT ≥ 80, approximate Bayes support ≥ 0.95, and ultrafast bootstrap support ≥ 95. The scale bar represents the number of substitutions per site. Sequences of Laonome sp. and Sabella pavonina Savigny, 1822 obtained from GenBank were used for outgroup rooting.

Figure 8. Light micrographs showing the morphologies of living spionid larvae of the genus Polydora A, B Polydora brevipalpa, dorsal view of 15 - chaetiger (A) and 17 - chaetiger larvae (B) C, D Polydora cornuta, dorsolateral view of 11 - chaetiger larva (C) and ventral view of 17 - chaetiger larva (D) E Polydora cf. glycymerica, dorsal view of 25 - chaetiger larva F Polydora hoplura, dorsal view of 15 - chaetiger larva G-I Polydora onagawaensis, dorsal view of 10 - chaetiger (G) and 18 - chaetiger larvae (H), and lateral view of 16 - chaetiger larva (I) J Polydora cf. spongicola, dorsal view of 17 - chaetiger larva K, L Polydora sp. 1, dorsal view of 7 - chaetiger (K) and 16 - chaetiger larvae (L) M Polydora sp. 2, dorsal view of 23 - chaetiger larva N-P Polydora sp. 3, dorsal view of 13 - chaetiger (N) and dorsal (O) and lateral view (P) of 18 - chaetiger larvae. Scale bars: 300 μm.