Paraprionospio coora Wilson, 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

Paraprionospio coora Wilson, 1990 Fig. 5A, B

Larval morphology.

Long and thin in shape, quite large and long body with numerous chaetigers. Prostomium anteriorly rounded, lateral lips elevated from the ventrolateral side of prostomium (Fig. 5A ). Late larvae acquire caruncle extending posteriorly from posterior part of prostomium (Fig. 5B ). Peristomium fuses with the first larval segment at late larval stage (Fig. 5B ). First pair of branchiae well developed, branchial pinnation still absent. Two pairs of red eyes arranged in somewhat trapezoidal shape, lateral pair kidney-shaped, situated anteriorly. Posterior part of pygidium pigmented reddish brown, anal cirri develop in late larvae.

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. Adult morphology agrees with the description of P. coora by Yokoyama (2007), and therefore this species was referred to P. coora . The larvae and adults were confirmed to match (18S: 1754/1754, 16S: 500/500 bp) using molecular data (Fig. 2 ).

Only three planktonic larvae of this species were found in Onagawa Bay in November 2011 and Sasuhama in January 2013. The morphological characteristics and size of these larvae are similar to those in previous descriptions of the species from the same genus ( Yokoyama 1981, 1996). However, the larvae of P. coora lack red pigmentation on the dorsolateral side of the lateral lips, which characterizes the larvae of Paraprionospio patiens Yokoyama, 2007 ( Yokoyama 1981; as P. pinnata : see Yokoyama 2007). Additionally, lamellae of the first pair of branchiae in P. coora are less developed in late larvae with more than 30 chaetigers (Fig. 5B ) compared with the larvae of P. patiens ( Yokoyama 1981) and Paraprionospio cordifolia Yokoyama, 2007 ( Yokoyama 1996, as Paraprionospio sp. form B: see Yokoyama 2007). Yokoyama (1981) suggested that the larvae of Paraprionospio are the largest in size and number of chaetigers at metamorphosis among the spionid larvae. However, late larvae of Poecilochaetus exceeding 5 mm ( Magalhães et al. 2015) and with more than 40 chaetigers are often reported ( Hannerz 1956; Plate and Husemann 1994).

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.