Spio sp. 1

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

Spio sp. 1 Fig. 9J, K

Larval morphology.

Overall larval shape slender and weakly fusiform. Larval chaetae on first chaetiger fairly long. Prostomium round anteriorly. Small patches of black pigment on peristomium ventrally. Three pairs of black eyes present, most lateral pairs double-eyes. Distinct black melanophore absent, rows of faint transverse band-shaped black pigmentation on dorsum from chaetiger IV onwards. Pharynx exhibits weak dark or brownish pigmentation. Gut yellow-green in color due to ingested food.

Remarks.

Adult individuals of this species were collected from Rishiri Island, northern Japan, in July and August 2017. These specimens were previously identified as S. arndti Meißner, Bick & Bastrop, 2011 ( Abe et al. 2019c) since adult morphology agreed. Although 18S rRNA gene sequence obtained in the present study 100% match with that of S. arndti (FR823434, 1761/1761 bp), because the 16S rRNA gene sequences were different (6.7%, 30/451 bp), the species reported here is referred to Spio sp. 1. The 16S rRNA gene sequence of Spio sp. 1 was rather more similar (96.1%, 298/310 bp) to that of Spio sp. 2573 from Russia (KT200126), but conspecificity of these two is unclear. A few planktonic larvae of this species were collected from Onagawa Bay only in May 2011. The larvae and adults were confirmed to match (18S: 1762/1762, 16S: 466/467 bp) using molecular data (Fig. 2 ).

The absence of distinct black melanophores in larvae of this species differentiates them from those of Spio sp. 2 (see below). Slight dorsal pigmentation was also reported in adelphophagic benthic larvae of Spio setosa Verrill, 1873 sensu Simon (1967, 1968), which were essentially unpigmented, and in those of Spio multioculata (Rioja, 1918) described by Hannerz (1956). However, the larval morphologies of these two species are different from that of Spio sp. 1 in lacking ventral black pigment on the peristomium (in both former species) and long larval chaetae on the first chaetiger (in S. setosa ), and in having a relatively thickened body shape (in both species).

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.