Polydora brevipalpa Zachs, 1933

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 brevipalpa Zachs, 1933 Fig. 8A, B

Larval morphology.

Overall shape slender and slightly fusiform. Prostomium broad and rounded anteriorly. Three pairs of black eyes present, innermost pair rounded, lateral pairs double-eyes, ramified melanophore between innermost and lateral two pairs of eyes usually present. Black pigment on lateral peristomium absent. Dorsal pigmentation consists of two rows of melanophores from chaetiger III. Dorsal melanophores undergo expansion and contraction, may expand to branching melanophores or ramified appearance or covered almost whole of dorsal surface by very finely ramified black pigments (Fig. 8B ), or they contract to dot-like pigmentation patches (Fig. 8A ). Lateral and ventral pigments absent. Vestibule and pharynx pigmented with black, gut pigmented with orange color. Modified chaetae develop on chaetiger V in late larvae. Gastrotrochs occur on chaetigers III, V, VII, X, XIII, XV, and XVII.

Remarks.

Adults of this species are boring and were collected from shells of cultured M. yessoensis scallops suspended in Onagawa Bay in February 2011 and Mutsu Bay in October 2011. This species was identified as P. brevipalpa as adult morphology agrees with the descriptions by Sato-Okoshi (1999) and Sato-Okoshi and Abe (2012). The larvae and adults were confirmed to 100% match using molecular data (Fig. 2 ).

Planktonic larvae of this species were collected from Onagawa Bay in April, May, and July 2011 and from Sasuhama in April 2011. The pair of large ramified or dot-like melanophores from chaetiger III distinguishes larvae of this species from those of other Polydora species. Blake (2017) reported similar dorsal pigment patterns in the larvae of Polydora spongicola Berkeley & Berkeley, 1950. However, the larvae of P. spongicola in Blake (2017) differ from those of P. brevipalpa in having dorsal melanophores from chaetiger II instead of chaetiger III, dark green colored intestine instead of orange, and non-pigmented pharynx instead of pigmented with black. Reproduction and life history of this species was reported in Sato-Okoshi et al. (1990) and Sato-Okoshi (1994) (both as P. variegata ).

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 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.