Spiophanes 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 uschakowi Zachs, 1933 Fig. 4M, N

Larval morphology.

Overall shape slender. Prostomium small and rounded anteriorly. Two pairs of red or dark red eyes present, lateral pair situated anteriorly. Late larvae bear very small antero-lateral processes on prostomium. Lateral parts of peristomium slightly demarcated from prostomium, palps attached on lateral-most parts of peristomium. Nototrochs occur from chaetiger IV onwards (Fig. 4N ). Yellow pigments on the prostomium and pygidium, intense yellow-brown pigment on peristomium, inside of pharynx, and pygidium. Small red pigment spots present on lateral part of body (Fig. 4N ). Black pigment in pharynx and proctodaeum absent.

Remarks.

No adult individuals of this species were collected in the present study. However, gene sequences obtained from larvae of this species were almost identical (18S: 1732/1732, 16S: 341/342 bp) to that of S. uschakowi (KM998760 and MG878915) from Russia ( Radashevsky et al. 2020a); therefore, this species was referred to S. uschakowi . Imajima (1991b) recorded four Spiophanes species from Japan: S. kroyeri Grube, 1860 (as S. kroeyeri ); S. japonicum Imajima, 1991; S. bombyx ( Claparède, 1870); and S. urceolata Imajima, 1991. Then, Meißner and Hutchings (2003) synonymized S. urceolata with S. wigleyi Pettibone, 1962. Additionally, the specimens from Japan formerly identified as S. bombyx were morphologically reexamined and identified as S. cf. uschakowi by Meißner and Blank (2009). In the present study, the presence of S. uschakowi in Japan was further supported by molecular analysis.

Only a few larvae of this species were collected in Onagawa Bay in November 2011. The overall larval morphology of this species somewhat resembles that of S. kroyeri described by Hannerz (1956) in the following aspects: prostomium is relatively small and anteriorly rounded, the peristomium is not quite sharply demarcated from the prostomium, nototrochs occur from chaetiger IV onwards, and the brown pigmentation is present on the pygidium and inside the pharynx. However, S. kroyeri lacks small red pigment spots on the lateral part of the body and lateral processes on the prostomium even in 22-chaetiger larvae.

Figures

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.