Pseudopolydora aff. achaeta Radashevsky & Hsieh, 2000

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 aff. achaeta Radashevsky & Hsieh, 2000 Fig. 9A, B

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 pairs double eyes. Mid-dorsal melanophore on first chaetiger present. Dorsal pigmentation consists of two pairs of lateral and central rows of melanophores. Lateral ones dot-like, beginning on chaetiger II. Central ones shaped like “tilted-wheels” (inverted v-shape) begin on chaetiger III. A central pair of dorsal pigment patches gradually become dot-like on posterior chaetiger. Weak mid-dorsal pigments occur from chaetiger VI. Two medial black pigmentation areas occasionally present ventrally, on approximately chaetiger VI and anterior margin of pygidium. Anterior and posterior margin of prostomium have considerable brown pigment. Black pigment spots occur on sides of prostomium and peristomium. Pygidium has a central black pigment spot. Gastrotrochs on chaetiger III, V, VII, and XII in 13-chaetiger larvae.

Remarks.

Adult individuals of this species were collected from muddy bottom sediments at 22 m depth in Onagawa Bay in December 2010 and September and December 2011 by using a Smith-McIntyre or Ekman-Birge grab sampler. Adult morphology agrees with the descriptions of P. achaeta by Radashevsky and Hsieh (2000) and Abe et al. (2016). However, the 16S rRNA gene sequence obtained in the present study showed a 11.5% (35/304 bp) difference with that of P. achaeta from Taiwan (country of type locality), which indicate that these two are different species. Therefore, this species is referred to P. aff. achaeta . The larvae and adults were confirmed to 100% match using molecular data (Fig. 2 ).

Planktonic larvae of this species with more than 3-chaetiger stages were abundant in Onagawa Bay during July to November ( Abe et al. 2014). A dorsal pigmentation area shaped like "tilted wheels" is a unique characteristic of this species among the known Pseudopolydora larvae.

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.