Spiophanes aff. uschakowi Zachs, 1933

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

Spiophanes aff. uschakowi Zachs, 1933 Fig. 4O, P

Larval morphology.

Overall shape slender. Prostomium broad and slightly notched anteriorly. In late larvae, a pair of prominent antero-lateral processes on prostomium developed. Two pairs of red or dark red eyes present, lateral ones situated somewhat anteriorly. Lateral parts of peristomium moderately demarcated from prostomium, palps on lateral-most parts of peristomium. Nototrochs occur from chaetiger II onwards. Pharynx and proctodaeum black in color internally. Pygidium acquires dorsal cirri in late larvae. Some brownish, yellowish, or greenish pigmentation occurred on various locations of body in late larvae.

Remarks.

Adult individuals of this species were collected from muddy bottom sediments at 22 m depth in Onagawa Bay in April and May 2012 by using a Smith-McIntyre grab sampler and from bottom sediments of the shallow subtidal zone in Sasuhama in February 2012. Adult morphology agrees with the description of S. cf. uschakowi by Meißner and Blank (2009) as well as with that of S. bombyx by Imajima (1991b). However, the 18S and 16S rRNA gene sequences of this species did not match those of S. uschakowi obtained from DDBJ/EMBL/GenBank (KM998760): there was a 0.29% (5/1750 bp) and 0.88% (3/342) difference, respectively between these two species. Therefore, this species was referred to S. aff. uschakowi . The larvae and adults were confirmed to 100% match using molecular data (Fig. 2 ).

Planktonic larvae of this species were collected in Onagawa Bay in November 2011 and in Sasuhama in February 2012. The larval morphology of S. aff. uschakowi was different from that of S. uschakowi in the following aspects: prostomium of the former is broad and slightly notched anteriorly, whereas that of the latter is relatively small and anteriorly rounded; the peristomium of the former is well demarcated from the prostomium, but that of the latter is relatively less demarcated; nototrochs of the former occur from chaetiger II onwards, whereas those of the latter occur from chaetiger IV onwards; pigmentation inside the pharynx is black in the former but brown in the latter; and black pigmentation in the proctodaeum is present in the former but absent in the latter. Black pigmentation in the pharynx and proctodaeum were also reported in the larvae of S. bombyx ( Hannerz 1956), S. cf. bombyx ( Blake 2006), and S. duplex (Chamberlin, 1919) ( Blake 2006). However, the illustrations of S. cf. bombyx provided by Blake (2006: fig. 13.10C, D) are seemingly more similar to larvae of Rhynchospio than to those of Spiophanes .

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.