Polydora onagawaensis Teramoto, Sato-Okoshi, Abe, Nishitani & Endo, 2013

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 onagawaensis Teramoto, Sato-Okoshi, Abe, Nishitani & Endo, 2013 Fig. 8G-I

Larval morphology.

Overall body shape slender. Prostomium slightly broad and rounded anteriorly. Three pairs of black eyes present; median pair of eyes rounded, most lateral pairs double-eyes. Ramified melanophore between middle and lateral pair of eyes usually present (Fig. 8G, H ). Weak brown pigmentation located on lateral parts of peristomium, behind prototroch, occasionally much paler or absent. Dorsal pigmentation consists of two rows of melanophores from chaetiger III with those of first IV-VI band-shaped and subsequently replaced by ramified melanophores. These melanophores undergo expansion and contraction. Lateral pigment found on chaetigers II and III in late larvae (Fig. 3G ). Dorsolateral pigment at base of most parapodia, often appears to coalesce with dorsal pigment bands on anterior part of body (Fig. 8H ). Pygidium has a dorsal notch and lacks appendages; a pair of black pigment patches occur on pygidium. Ventral brown pigment may be present on posterior part of late larvae (Fig. 8I ). Telotroch well developed. Gastrotrochs on chaetigers III, V, VII, X, XIII, and XV; those of chaetigers III and V lost in late larvae (Fig. 8I ). In late larvae, modified chaetae develop in chaetiger V.

Remarks.

This species is a shell-borer, and adult individuals were collected from shells of the wild turban snail O. rusticus , cultured scallop M. yessoensis , and wild and cultured C. gigas oysters in Onagawa Bay and Sasuhama, northeastern Japan. This species was identified as P. onagawaensis as adult morphology agrees with the description by Teramoto et al. (2013). The larvae and adults were confirmed to match (18S: 1771/1771, 16S: 472/473 bp) using molecular data (Fig. 2 ).

Planktonic larvae of this species were abundant from November to June in Onagawa Bay during the study period. The larval morphology of this species is similar to that of Polydora sp. 3 (see below). However, the former species has weak brown pigmentation on the lateral parts of the peristomium, whereas the latter species has large patches of black pigment on this region.

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.