Pseudopolydora cf. reticulata 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 cf. reticulata Radashevsky & Hsieh, 2000 Fig. 9E, F

Larval morphology.

Overall larval shape fusiform, head region enlarged due to broad prostomium and expanded lateral lips of vestibule. Prostomium slightly notched anteriorly. Three pairs of black eyes present in more or less a straight line, most lateral pairs double-eyes. Large patches of black pigment on lateral peristomium present. Mid-dorsal melanophore on chaetiger I usually present. Dorsal pigments undergo expansion and contraction, expanding to cover almost complete dorsal surface with finely ramified black pigment (Fig. 9F ) or contract to dot-like black pigmentation without ramifications (Fig. 9E ). Ventral pigment usually absent, consisting of paired bars on the posterior border on anterior chaetigers occasionally present. Black pigment on pygidium. Gastrotrochs on chaetigers V, VII, and XII in 17- and 18-chaetiger larvae, late larvae lose gastrotrochs on chaetigers V and/or XXII.

Remarks.

Adult individuals of this species were collected from muddy sediment in Gamo Lagoon in April 2013 and Sasuhama in July and September in 2011. Adult morphology agrees with the description of P. cf. reticulata by Abe et al. (2016). Therefore, these individuals were referred to this species. The 16S rRNA gene sequence obtained in the present study showed a 99.4% (304/306 bp) similarity with that of P. bassarginensis (Zachs, 1933) from Russia (MG460894) reported by Radashevsky et al. (2020b), indicating these two are one species. Although the Japanese population shows intermediate morphological characteristics between P. reticulata (type locality Taiwan) and P. bassarginensis (type locality Russia), Abe et al. (2016) tentatively identified the Japanese population as P. cf. reticulata because the original description of P. bassarginensis is very brief and the status of the species remains unclear. The results of the present study indicate that the Japanese population likely belongs to P. bassarginensis , but whether the morphologically similar P. reticulata and P. bassarginensis are considered molecularly as the same or different species will need to be clarified. Planktonic larvae of P. cf. reticulata larger than the 3-chaetiger stage were collected from Gamo Lagoon, Sasuhama, and Onagawa Bay mainly from July to September. The larvae and adults were confirmed to match (18S: 1775/1775, 16S: 468/470 bp) using molecular data (Fig. 2 ).

Pseudopolydora cf. reticulata and P. cf. kempi are very similar sister species; specimens from Japan once misidentified as P. cf. kempi or P. kempi japonica were distinguished based on their morphology and 18S and 28S rRNA gene sequences by Abe et al. (2016). The larvae of these two species are also quite similar, but the mid-dorsal melanophore on chaetiger I is usually present in Ps. cf. reticulata and absent in P. cf. kempi ; moreover, the dorsal pigmentation is more distinct in the former species than in the latter. The two species also differ in reproduction and larval development: P. cf. kempi has lecithotrophic development with a short planktonic phase, whereas P. cf. reticulata has planktotrophic development with a long planktonic phase ( Kondoh et al. 2017).

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.