Polydora cf. glycymerica Radashevsky, 1993

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. glycymerica Radashevsky, 1993 Fig. 8E

Larval morphology.

Overall shape elongated and slender. Prostomium small and rounded anteriorly. Three pairs of black eyes present, most lateral pairs double-eyes. Ramified melanophores between middle and lateral pair of eyes absent. Pigmentation on lateral peristomium absent. Two rows of ramified melanophores on chaetigers III-VI, and a median row of ramified melanophores from chaetiger VII onwards. Lateral and ventral pigments absent. A pair of black pigments occur on pygidium. Pygidium has a dorsal notch and lacks appendages. Gastrotrochs absent in 25-chaetiger larvae, probably already lost. Modified chaetae develop on chaetiger V.

Remarks.

No adult individuals of this species were collected in the present study. The 18S and 16S rRNA gene sequences obtained from larvae in the present study did not match any of the available Polydora sequences. However, as the larvae formed a robustly supported clade with other Polydora species (Figs 2 , 3 ), this species was referred to as the genus Polydora . Furthermore, the larval morphology including the characteristic dorsal pigment pattern of this larvae matches that of the larvae of P. glycymerica described by Radashevsky (1989). Therefore, this larva was tentatively identified as P. cf. glycymerica . However, there were slight differences between the present specimens and Radashevsky (1989) description: the two rows of ramified melanophores continued until chaetiger VI in the present description, whereas it continues to chaetigers VII-X according to Radashevsky (1989); ramified melanophores between the middle and lateral pair of eyes are present in the former description while absent in the latter; larvae of P. cf. glycymerica collected in the present study were 25-chaetigers with> 2.0 mm long (Fig. 8E ), whereas the largest larva observed by Radashevsky (1989) was a 20-chaetiger specimen 1.8 mm long. Further studies should test whether these differences are attributable to individual or developmental variabilities or interspecific differences.

The dorsal median single row of ramified melanophores is distinct in the larvae of the genus Polydora . The larvae of Polydora hermaphroditica also have a dorsal median row of ramified melanophores such as that of the larvae of P. cf. glycymerica and P. glycymerica ( Hannerz 1956; Plate and Husemann 1994). However, the first species differs from the other two by the absence of two rows of ramified melanophores on anterior chaetigers.

Only one individual of planktonic larva of P. cf. glycymerica was collected in Onagawa Bay in October 2011. Polydora glycymerica was previously recorded as a shell-borer of Macridiscus aequilatera (G. B. Sowerby I, 1825) from Oarai, Japan ( Sato-Okoshi 1999).

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.