Molecular identification and larval morphology of spionid polychaetes (Annelida, Spionidae) from northeastern Japan Author Abe, Hirokazu https://orcid.org/0000-0002-7753-9368 Department of Biology, Center for Liberal Arts & Sciences, Iwate Medical University, Idaidori 1 - 1 - 1, Yahaba-cho, Shiwa-gun, Iwate 028 - 3694, Japan habe@iwate-med.ac.jp Author Sato-Okoshi, Waka Laboratory of Biological Oceanography, Graduate School of Agricultural Science, Tohoku University, Aramaki-Aza-Aoba 468 - 1, Aoba-ku, Sendai 980 - 8572, Japan text ZooKeys 2021 2021-02-04 1015 1 86 http://dx.doi.org/10.3897/zookeys.1015.54387 journal article http://dx.doi.org/10.3897/zookeys.1015.54387 1313-2970-1015-1 F6BD92139DB74564AA003C61B2F43B2D AF1641758561525C8D40BBF3F895FA8A 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 ; Guerin 1972 ; Srikrishnadhas and Ramamoorthi 1981 ; Plate and Husemann 1994 ).