Spio sp. 2

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

Spio sp. 2 Fig. 9L-N

Larval morphology.

Overall larval shape elongated, slender, weakly fusiform. Larval chaetae on first chaetiger fairly long. Prostomium round anteriorly. Small patches of black pigment on lateral peristomium present ventrally. Three pairs of black eyes present, most lateral pairs double-eyes. Two rows of dot-like black melanophores on each side of dorsum from chaetiger I onwards, linking by band-shaped medial black pigmentation from chaetiger IV or V. Pharynx exhibits weak dark or brownish pigmentation. The larvae which are ready to metamorphose have branchiae from chaetiger II, pigment spot on palps, and a pygidium with four leaf-shaped anal cirri.

Remarks.

Adult individuals were collected from muddy sand sediments of shallow water in Sasuhama in September 2011. These adults were morphologically identified as a Spio species, but they could not be identified to species level. Spio spp. 1 and 2 are distinguishable morphologically by the number of ventral epidermal glands. The 18S and 16S rRNA gene sequences obtained in the present study did not match any of the available Spio sequences (Figs 2 , 3 ). The larvae and adults were confirmed to 100% match using molecular data (Fig. 2 ).

Planktonic larvae of this species were found in Sasuhama and Onagawa Bay from April to August during the study period. Larval morphology and pigmentation pattern of this species is similar to that of Spio decorata Bobretzky, 1870 described by Guérin 1972. However, the latter species was originally described from the Black Sea and has not been recorded in Japan.

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 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.