Prionospio membranacea Imajima, 1990

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

Prionospio membranacea Imajima, 1990 Fig. 5E-G

Larval morphology.

Long and thin in shape. Prostomium rounded anteriorly, lateral parts of peristomium not especially well demarcated. Two pairs of red or dark red eyes arranged somewhat in trapezoidal shape, lateral pair kidney-shaped and situated anteriorly. Small caruncle develop in late larvae, extends posteriorly from posterior part of prostomium (Fig. 5G ). In late larvae branchial anlages occur from chaetiger II, pygidium acquires anal cirri (Fig. 5G ). Palps not yet developed in 15- and 20-chaetiger larva (Fig. 5E, F ) but developed in 24-chaetiger larva (Fig. 5G ). Pigmentation absent except eyes.

Remarks.

Adult individuals of this species were collected from muddy bottom sediments at 22 m depth in Onagawa Bay in December 2011 by using a Smith-McIntyre grab sampler. The species was referred to P. membranacea as the adult morphology agrees with the descriptions of this species by Imajima (1990b). The larvae and adults were confirmed to match (18S: 1752/1752 and 1747/1750 except for gaps, 16S: 502/505 bp) using molecular data (Fig. 2 ). Planktonic larvae of this species were found in Onagawa Bay during August to October.

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 5. Light micrographs showing the morphologies of living spionid larvae of genera Paraprionospio and Prionospio A, B Paraprionospio coora, lateral view of 25 - chaetiger (A) and 33 - chaetiger larvae (B) C, D Prionospio krusadensis, lateral view of 17 - chaetiger larvae E-G Prionospio membranacea, lateral view of 15 - chaetiger (E), 20 - chaetiger (F), and 24 - chaetiger larvae (G) H, Prionospio sp. 1, lateral view of 11 - chaetiger larva I Prionospio sp. 2, lateral view of 19 - chaetiger larva. Scale bars: 300 μm.