Polydora hoplura Claparede , 1868

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 hoplura Claparede, 1868 Fig. 8F

Larval morphology.

Overall body shape slender or somewhat fusiform. Prostomium broad and rounded anteriorly. Three pairs of black eyes present, most lateral pairs double-eyes. Ramified melanophores between first and second innermost pair of eyes absent. Black pigmentation patches on lateral peristomium absent. Dorsal pigmentation consists of two rows of melanophores from chaetiger III with those of first five pairs band-shaped and then replaced by ramified melanophores in posterior chaetigers. Lateral pigments found on late larvae on chaetigers II-IV. Dorsolateral pigments at base of the parapodia start from chaetiger VII. A pair of black pigment occur on pygidium. Ventral pigment absent. Modified chaetae develop in chaetiger V in late larvae. Gastrotrochs occur on chaetigers III, V, VII, X, XIII, and XV.

Remarks.

This species is a shell-borer, and adult specimens were collected from the turban snail Omphalius rusticus (Gmelin, 1791) in Gobu-ura and Onagawa Bay. This species was identified as P. hoplura as its adult morphology agrees with descriptions by Sato-Okoshi and Abe (2012, as P. uncinata ) and Sato-Okoshi et al. (2017). The larvae and adults were confirmed to match (18S: 1769/1769, 16S: 464/475 bp) using molecular data (Fig. 2 ).

Only late larvae were found in July in Onagawa Bay. The larval morphology of this species agrees with descriptions by Wilson (1928) and Radashevsky and Migotto (2017). This species has adelphophagic and lecithotrophic larval development, in which larvae feed on nurse eggs in brood capsules, hatch at a very late stage, and have only a short pelagic life ( Wilson 1928; Read 1975; Sato-Okoshi et al. 2008, as P. uncinata ; Radashevsky and Migotto 2017). The poecilogenous development of this species with planktotrophic and adelphophagic planktonic larvae was reported by David et al. (2014), David and Simon (2014), and Simon (2015).

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.