Aonides aff. oxycephala (Sars, 1862)

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

Aonides aff. oxycephala (Sars, 1862) Fig. 4A-C

Larval morphology.

Remnants of egg envelope apparent in early trochophore (Fig. 4A ). In ten-chaetiger larvae, egg envelope becomes incorporated into larval cuticle, two pairs of red eyes arranged in an approximately straight line (Fig. 4B ). Larval chaetae on first chaetiger long especially in early larvae (Fig. 4A, B ). Late larvae long and slender in shape (Fig. 4C ). Prostomium rectangular anteriorly in larval stages, considerably extended and tapered in juvenile stage. Lateral parts of peristomium moderately demarcated from prostomium. Black pigment in pharynx. Pigmentation absent except in the eyes and pharynx. Pygidium acquires two pairs of dorsal cirri in late larvae (Fig. 4C ).

Remarks.

Adult individuals of this species were collected from muddy bottom sediment at 22 m depth in Onagawa Bay in January 2011 and 2012 using a Smith-McIntyre grab sampler. Adult morphology agrees with the description of A. oxycephala by Imajima (1989). Aonides oxycephala originally described from Norway has been reported worldwide and is considered cosmopolitan. However, these reports may comprise a series of similar or sibling species, as pointed out by Radashevsky (2015). The gene sequences obtained in the present study were 100% match in 18S rRNA but 8.6% (29/337 bp) different in 16S rRNA from that of A. oxycephala from France (MG913226 and MG878895). Therefore, the species collected in the present study was referred to A. aff. oxycephala . The larvae and adults were confirmed to match (18S: 1753/1753, 16S: 447/448 bp) using molecular data (Fig. 2 ).

Planktonic larvae were found in Onagawa Bay from October to December. In early larval stages, the larvae of this species are similar to those of Laonice sp. (Fig. 4D ); but larval chaetae are longer, and the body is yolkier and opaquer in this species. The larval morphology of A. aff. oxycephala is similar to that of A. oxycephala described by Hannerz (1956). However, the peristomium of the former species is more developed and demarcated from the prostomium compared to the latter. Black pigmentation of the pharynx in late larval stages was not reported by Hannerz (1956).

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 4. Light micrographs showing morphologies of living spionid larvae of Aonides, Laonice, Rhynchospio, Scolelepis, and Spiophanes A-C Aonides cf. oxycephala, dorsal view of early planktonic (A), 8 - chaetiger (B), and 18 - chaetiger larvae (C) D Laonice sp. 1, dorsal view of early planktonic larva E Laonice sp. 2, dorsal view of 12 - chaetiger larva F Poecilochaetus sp., dorsal view of 17 - chaetiger larva G, H Rhynchospio aff. asiatica, dorsal view of 6 - chaetiger (G) and 12 - chaetiger larvae (H) I Scolelepis cf. kudenovi, dorsal view of 7 - chaetiger larva J, K Scolelepis sp. 1, dorsal view of 17 - chaetiger (J) and 19 - chaetiger larvae (K) L Scolelepis sp. 2, dorsal view of 20 - chaetiger larva M, N Spiophanes uschakowi, dorsal (M) and lateral view (N) of 18 - chaetiger larvae O, P Spiophanes aff. uschakowi, dorsal view of 16 - chaetiger larva (O) and 27 - chaetiger juvenile (P). Scale bars: 300 μm.