Polydora cf. spongicola Berkley & Berkeley, 1950

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 cf. spongicola Berkley & Berkeley, 1950 Fig. 8J

Larval morphology.

Overall body shape slender and slightly fusiform. Prostomium broad and rounded anteriorly. Three pairs of black eyes present; median eyes rounded, most lateral pairs double-eyes. Ramified melanophores between middle and lateral pair of eyes absent. Black pigment on lateral peristomium absent. Dorsal pigmentation consists of two rows of band-shaped melanophores from chaetiger II. These melanophores undergo expansion and contraction, expand to ramified melanophores or contract to non-ramified band-shaped melanophores. Lateral and ventral pigments absent. In late larvae modified chaetae develop in chaetiger V. Gastrotrochs on chaetigers III, V, VII, X, XIII, and XV.

Remarks.

Adults of this species were collected from mud tubes constructed on the sponge Mycale sp. in Moroiso Bay, Misaki Peninsula (Table 1 ). The morphology of its modified spines in chaetiger V and the sponge-associated ecology of adults match the description of P. spongicola by Radashevsky (1993). However, this species was referred to P. cf. spongicola because the adult specimens were in poor condition, which hindered their morphology examination. The larvae and adults were confirmed to match (18S: 1770/1771, 16S: 474/475 bp) using molecular data (Fig. 2 ).

Only one planktonic larva of this species was collected in Sasuhama in January 2013. The larval morphology of P. cf. spongicola closely resembles that of P. spongicola described by Radashevsky (1988, as Polydora uschakovi Buzhinskaja, 1971) from Russia. Polydora uschakovi originally described from Russia was synonymized with P. spongicola (type locality: Canada) by Radashevsky (1993). Later, Blake (2017) described the larvae of P. spongicola from California and doubted this synonymization because, despite the similarities between the larvae from Russian and California, there are several morphological differences including the nature of the major spines of chaetiger V and the distribution of nototrochs and gastrotrichs. However, the larval dorsal pigment pattern of P. spongicola described by Blake (2017) greatly differs from those of P. cf. spongicola in the present study and of P. spongicola in Radashevsky (1988) but resembles that of P. brevipalpa in the present study. Conspecificity between P. uschakovi and P. spongicola should be verified in future studies.

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.