Boccardia proboscidea Hartman, 1940

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

Boccardia proboscidea Hartman, 1940 Fig. 7A, B

Larval morphology.

Slender and fusiform in overall shape, widest in middle of body. Prostomium rounded and slightly notched anteriorly. Three pairs of eyes present, most median pair rounded, lateral pairs double-eyes. Body entirely faint green in color. A prominent row of dorsal melanophores occurs medially from chaetiger III, lateral black pigment spots present on chaetigers VII and VIII in late larvae (Fig. 7B ). Pygidium has dorsal gap, pigmented with weak dark color. Internally, vestibule light brown, gut either yellow or brown. Gastrotrochs on chaetigers V and VII.

Remarks.

Adults of this species were non-boring and collected from mud deposits in crevices of shells of living Crassostrea gigas (Thunberg, 1793) (recently assigned to Magallana : see Backeljau 2018) oysters in Sasuhama in May 2011 and February 2016. Adult morphology agrees with the description of B. proboscidea by Sato-Okoshi (2000). The 18S and 16S rRNA gene sequences obtained in the present study match (18S: 1748/1748, 16S: 435/435 bp) that of B. proboscidea from USA (KJ546254) reported by Radashevsky et al. (2014) (Fig. 3 ). Therefore, this species was referred to B. proboscidea . The larvae and adults were confirmed to match (18S: 1768/1768, 16S: 472/472 bp) using molecular data (Fig. 2 ).

Planktonic larvae of this species were rare, and only one 15-chaetiger larva (Fig. 7B ) was collected in Sasuhama in May 2011. Another 9-chaetiger larvae, which accidentally hatched from its egg capsule in an adult tube during the process of extraction of the adult specimens (Fig. 7A ), was also collected on the same date. Boccardia proboscidea has been reported to have poecilogonous development ( Gibson 1997; Oyarzun et al. 2011). However, Sato-Okoshi (2000) reported that Japanese populations only show lecithotrophic development, with no (or a very short) planktonic stage after hatching. The larval morphology of this species agrees with the description of that of B. proboscidea documented in Hartman (1941), Woodwick (1977), Blake and Kudenov (1981), Gibson (1997), Gibson and Smith (2004), Kamel et al. (2010), and Oyarzun and Brante (2015). The dorsal pigment pattern of these larvae resembles that of the larvae of B. tricuspa (Hartman, 1939) described by Carrasco (1976, as B. proboscidea ; fide Blake and Kudenov 1978), B. natrix ( Söderström, 1920) described by Söderström (1920, as Polydora natrix ), and B. columbiana Berkeley, 1927 described by Blake and Arnofsky (1999) and Blake (2006) in having a single row of mid-dorsal melanophores. However, the dorsal pigment pattern of the larvae of B. tricuspa differs from that of B. proboscidea in having branching dorsal melanophores on chaetiger I and in lacking small black lateral pigment spots on chaetigers VII and VIII. The larvae of B. natrix also lack small black lateral pigment spots on chaetigers VII and VIII. Boccardia columbiana has extensively branching mid-dorsal melanophores from chaetiger II onward, whereas mid-dorsal melanophores are less branching and start from chaetiger III in B. proboscidea .

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 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.