Spio Fabricius, 1785

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

Genus Spio Fabricius, 1785

Larval diagnosis.

Overall body shape long, slender, and weakly or moderately fusiform. Prostomium small and rounded anteriorly. Lateral part of peristomium weakly demarcated from prostomium. Three pairs of black eyes present, most lateral often double-eyes. Dorsal pigmentation consists of transverse band-shaped or dot-like paired lateral melanophores. Some species lack black pigmentation. Ventral pigment usually absent. Dark-brown pigment may be present on pygidium. Nototrochs occur in all chaetigers except first one or two chaetigers, where nuchal organs develop. Gastrotrochs occur regularly in every other chaetiger from chaetiger III onwards. Larval chaetae on first chaetiger usually fairly long. Branchiae develop in late larvae, first on chaetiger II or III. One pair of anal cirri present on pygidium in late larvae ( Thorson 1946, as spionid larva C, E, and F; Hannerz 1956; Wu et al. 1965; Simon 1963, 1967, 1968; Guérin 1972; Srikrishnadhas and Ramamoorthi 1981; Plate and Husemann 1994).