Dipolydora giardi (Mesnil, 1896)

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

Dipolydora giardi (Mesnil, 1896) Fig. 7M, N

Larval morphology.

Overall body shape elongated and slender. Prostomium small and rounded anteriorly. Three pairs of black eyes arranged in transverse row, most lateral pairs double-eyes. Black pigmentation on lateral peristomium absent. Two pairs of dorsal black spots begin on chaetiger III onwards and continue to posterior end, sometime medial pair in first 2-4 chaetigers band-shaped. Small medial spot of black pigment on posterior margin of each chaetiger usually from chaetigers III, rarely from V or VI, in late larvae. Two small spots of black pigmentation occur lateral to the medial black pigmentation from approximately chaetiger VI or VII. A small black pigment spot, not visible dorsally, present on antero-lateral edges from chaetiger II onwards. Black pigment occurs on pygidium. Rust-colored pigment occurs in pharynx. Ventral pigment absent. Some metamorphosing larvae reduce pigmentation over the entire body and present whitish appearance with eyes fused and appears as one pair (Fig. 7N ). Gastrotrochs on chaetigers III, V, VII, X, XIII, and XV.

Remarks.

Adults of this species are shell-borers and were collected from shells of cultured Mizuhopecten yessoensis (Jay, 1857) (formerly as Patinopecten yessoensis ) scallops suspended in Onagawa Bay in December 2010. Adult morphology agrees with the description of D. giardi by Sato-Okoshi (1999). Therefore, this species was referred to D. giardi . The larvae and adults were confirmed to match using molecular data (Fig. 3 ).

The 18S rRNA gene sequences of this species are very similar to that of D. capensis 1PE from South Africa (KY677896) reported by Williams et al. (2017), but there is a slight difference between their sequences (0.12% difference: 2/1714 bp). It is unclear whether this difference indicates that these two are the same or different species because two different 18S rRNA gene sequences have been reported from South Africa and are currently under the same species name ( D. capensis ) (Table 2 , Fig. 3 ). No gene sequences of D. cf. giardi previously recorded from South Africa ( Simon 2011) are available.

Planktonic larvae of this species were collected from Onagawa Bay in December 2010, June, July, October, November, and December 2011, and December 2012, and from Sasuhama in January 2013. The larval morphology of this species was previously described from California by Day and Blake (1979, as Polydora giardi ). The morphology and dorsal pigment pattern of late larvae described by these authors resembles that reported here, but there are slight differences: two golden pigment spots present on either side of chaetiger I in the former description but absent in the latter; two small lateral melanophores present on chaetigers I and II in the former description but absent in the latter; a medial black pigmentation beginning from chaetiger II onwards in the former description but from chaetiger III onwards in the latter description; and two small spots of black pigmentation lateral to the medial black pigmentation starting from chaetiger III in the former description but from more posteriorly in the latter description. These differences between specimens from Japan and California may indicate that they are different species, or that intraspecific variation occurs in larval dorsal pigmentation. Day and Blake (1979) pointed out differences in reproductive traits between the Californian and French populations and suggested the existence of two different species. Therefore, more than one species may be included under the name of D. giardi , which currently is reported with a worldwide distribution ( Radashevsky and Petersen 2005).

Figures

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 7. Light micrographs showing the morphologies of living spionid larvae of genera Boccardia, Boccardiella, and Dipolydora A, B Boccardia proboscidea, dorsal view of accidentally hatched 9 - chaetiger (A) and 15 - chaetiger larvae (B) C Boccardia pseudonatrix, dorsal (left) and ventral (right) view of accidentally hatched 10 - chaetiger larvae D-F Boccardia sp. 1, dorsal view of 9 - chaetiger (D) and dorsal (E) and ventral view (F) of 17 - chaetiger larvae G Boccardia sp. 2, dorsal view of 15 - chaetiger larva H, I Boccardiella hamata, dorsal view of 16 - chaetiger (H) and 18 - chaetiger larvae (I) J, K Dipolydora bidentata, dorsal view of 13 - chaetiger (J) and 18 - chaetiger larvae (K) L Dipolydora cf. commensalis, dorsal view of 21 - chaetiger larva M, N Dipolydora giardi, dorsal view of 19 - chaetiger (M) and lateral view of 21 - chaetiger larvae (N) O Dipolydora cf. socialis, dorsal view of 18 - chaetiger larva P Dipolydora sp., dorsal view of 7 - chaetiger larva. Scale bars: 300 μm.