Spio Fabricius, 1785

Prostomium blunt, anteriorly truncate or rounded, anterior margin with entire anterior margin or bifid, with anterior margin indented. Lateral horns absent. Caruncle present. Occipital antenna absent. Nuchal organ short, at most one segment long. Eyes present, or absent. Palps simple, lacking basal sheath. Dorsal ridge connecting bases of branchiae on chaetiger 1 absent. Prominent dorsal collar on setiger 2 absent. Dorsal branchiae present, first present on chaetiger 1. Dorsal branchiae continue to near posterior end of body. Dorsal branchiae continuous. Dorsal branchiae free and separate from notopodial lamellae throughout or partially or wholly fused with notopodial lamellae (on some or all chaetigers), all simple. First branchiae without process at base on anterior face. Accessory branchiae arising from posterior part of notopodium absent. Ventral branchiae absent. Chaetiger 3 without filament at base of branchiae. Dorsal crests absent. Ventral crests absent. Chaetiger 1 notopodium present. Chaetiger 1 notochaetae present. Neuropodial lobe of chaetiger 2 rounded, approximately symmetrical. Neuropodial lobes of posterior chaetigers a single lobe. Interparapodial pouches absent. Chaetigers 2–4 similar, not strongly differentiated. Chaetiger 5 unmodified, similar to subsequent chaetigers. Posterior modified notochaetae absent. Notopodial hooded hooks absent. Neurochaetae of chaetiger 1 simple capillaries similar to those of subsequent chaetigers. Neuropodial hooded hooks present. Neuropodial hooded hooks with accessory tooth or teeth above the main fang, 2 accessory teeth (tridentate) or 3 accessory teeth (quadridentate) or multiple accessory teeth (more than 3). Shaft of neuropodial hooded hooks of constant thickness, lacking a constriction. Neuropodial sabre chaetae present, in ventral-most positions or absent. Neuropodial spines absent. Embedded bunches of notopodial needle chaetae absent. Pygidium with 4 anal cirri.

Description generated from: Wilson, RS & McDiarmid, H 2013. Spionidae (Polychaeta)- A DELTA database of genera, and Australian species. Version 2; originally published as In RS Wilson, PA Hutchings & CJ Glasby (eds) Polychaetes: An Interactive Identification Guide. CSIRO Publishing, Melbourne.

Additional references:
Blake, JA and Kudenov, JD. 1978. The Spionidae (Polychaeta) from southeastern Australia and adjacent areas with a revision of the genera. Memoirs of the National Museum of Victoria 39, 171-280.