Pseudopolydora paucibranchiata (Okuda, 1937)

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

Pseudopolydora paucibranchiata (Okuda, 1937) Fig. 9D

Larval morphology.

Overall body shape fusiform, head region enlarged due to broad prostomium and expanded lateral lips of vestibule. Prostomium gently notched anteriorly. Three pairs of black eyes present in more or less a straight line, most lateral pair comma-shaped. A mid-dorsal ramified melanophore on chaetiger I. A pair of melanophores present dorso-laterally from chaetigers II onwards. Black pigment spots occur on lateral surface of chaetiger II, on sides of peristomium, and pygidium. Two small medial black pigment spots occasionally present ventrally on approximately chaetiger VI and anterior margin of pygidium. Gut has yellow-green color due to ingested food. Gastrotrochs on chaetiger V, VII, and XI in 13-chaetiger larvae.

Remarks.

Adult individuals were collected from muddy bottom sediment in the intertidal zone of Mangoku-ura Inlet in July 2014. Adult morphology agrees with the description of Pseudopolydora paucibranchiata by Okuda (1937, as Polydora ). Therefore, these individuals were referred to this species. The larvae and adults were confirmed matching (18S: 1784/1784, 16S: 454/455 bp) using molecular data (Fig. 2 ).

The planktonic larvae of this species were reported to be common in Onagawa Bay during June to November ( Abe et al. 2014). The larval morphology of this species observed in the present study agrees with the descriptions by Blake and Woodwick (1975), Ward (1977), Myohara (1980), Wu and Chen (1980), Radashevsky (1983), and Blake (2006). The dorsal pigment pattern of this species consists of one pair of melanophores, which agrees with that of the larvae of Pseudopolydora vexillosa Radashevsky & Hsieh, 2000 photographed by Mok et al. (2009) and Chandramouli et al. (2011, 2013), currently synonymized to P. paucibranchiata ( Junqueira et al. 2009). The dorsal pigment pattern of these larvae is also similar to that of the larvae of Pseudopolydora antennata ( Claparède, 1869) described by Hannerz (1956, as Polydora antennata ), but the latter species has a more thickened body shape compared to the former.

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 9. Light micrographs showing the morphologies of living spionid larvae of genera Pseudopolydora and Spio A, B Pseudopolydora aff. achaeta, dorsal view of 12 - chaetiger (A) and 25 - chetiger larvae (B) C Pseudopolydora cf. kempi, dorsolateral view of 12 - chetiger larva D Pseudopolydora paucibranchiata, dorsal view of 13 - chaetiger larva E, F Pseudopolydora cf. reticulata, dorsal view of 17 - chaetiger (E) and 16 - chaetiger larvae (F) G, H Pseudopolydora tsubaki, dorsal view of 5 - chaetiger (G) and 11 - chaetiger larvae (H) I Pseudopolydora sp., dorsal view of 7 - chaetiger larva J, K Spio sp. 1, dorsal view of 8 - chaetiger (J) and lateral view of 12 - chaetiger larvae (K) L-N Spio sp. 2, dorsal view of 10 - chaetiger (L) and 17 - chaetiger larvae (M), and 17 - chaetiger metamorphosing larvae (N). Scale bars: 300 μm.