Polydora sp. 2

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. 2 Fig. 8M

Larval morphology.

Overall body shape slender. Prostomium broad and rounded anteriorly. Three pairs of black eyes present, most lateral pairs double-eyes. Ramified melanophores between first and second innermost pairs of eyes absent. Pigmentation on lateral peristomium weak brown or absent. Dorsal pigmentation consists of two rows of melanophores from chaetiger II, with those of first 4-6 chaetigers being band-shaped and then replaced by ramified melanophores in posterior chaetigers. Dorsal pigments faint, undergo expansion and contraction, expand to cover almost whole of dorsal surface as finely ramified black pigmentation (Fig. 8M ) or contract to band-shaped or dot-like black pigments without ramification. Faint lateral pigment found on late larvae on chaetigers VII onwards. Ventral pigments absent. A pair of brown pigments occur on the pygidium. Pygidium has a dorsal notch and lacks appendages. Gastrotrochs on chaetigers III, V, VII, X, XIII, XV, XVII, and XIX. Modified chaetae develop in chaetiger V in late larvae.

Remarks.

No benthic adult stages were collected in the present study. These larvae formed a robustly supported monophyletic clade with other Polydora species (Figs 2 , 3 ). Nevertheless, this species was identified as a member of Polydora . As the 18S and 16S rRNA gene sequences obtained from the larvae did not match any other available Polydora sequences, this species was referred to Polydora sp. 2.

Only two individuals of planktonic larvae of this species were collected from Sasuhama and Gamo Lagoon in January 2013. The faint dorsal pigmentation of the larvae of this species is unique among the members of Polydora collected in the present study.

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.