Pseudopolydora tsubaki Simon, Sato-Okoshi & Abe, 2017

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 tsubaki Simon, Sato-Okoshi & Abe, 2017 Fig. 9G, H

Larval morphology.

Overall larval 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, comprising one pair of rounded median eyes, one pair of large lateral eyes, and one pair of large anterior eyes. Lateral and anterior pairs of eyes link with each other and form dumbbell-shapes almost divided into two equal parts by a deep constriction. Mid-dorsal ramified melanophore present on chaetiger I in early larvae. Mid-dorsal melanophore on chaetiger I occasionally absent or expanded to finely ramified melanophore in late larvae. A paired of melanophores occur dorso-laterally from chaetiger II onwards, usually finely ramified in late larvae (Fig. 9H ). Ramified melanophores cover almost entire ventral surface on chaetigers III-VII in 11-chaetiger larvae. Black pigment spots on sides of peristomium absent. Conspicuous large black pigment on pygidium. Gastrotrochs on chaetigers V and VII in 11-chaetiger larvae.

Remarks.

Adult individuals were collected from mud deposits in crevices of shells of living C. gigas oysters in Habu Port, Izu-Oshima Island, and Tomiura, Boso Peninsula in April 2016. Adult morphology agrees with the description of Pseudopolydora tsubaki by Simon et al. (2019a). Therefore, these individuals were identified as P. tsubaki . The larvae and adults were confirmed to 100% match using molecular data (Fig. 2 ).

A small number of planktonic larvae of this species were collected in Habu Port and Tomiura in May and June 2016. The larvae of P. tsubaki are similar to those of Pseudopolydora pulchra (Carazzi, 1893) in having ramified melanophores covering the ventral side; however, these cover only the central part of the body in the former species, whereas those of latter species cover the ventral surface almost entirely ( Hannerz 1956, as Polydora pulchra ; Rullier 1963, as Polydora pulchra ). The dorsal pigment pattern is also different in these two species: two pairs of melanophores are distinct in P. pulchra , whereas the melanophore pair is ambiguous in P. tsubaki .

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.