Spio readi Blake, 1984

Prostomium blunt, anteriorly truncate or rounded, anterior margin with entire anterior margin. Lateral horns absent. Caruncle present, continuing back to chaetiger 3. Occipital antenna absent. Nuchal organ short, at most one segment long. Eyes present; 4 eyes. 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 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, first present on chaetiger 11. Neuropodial hooded hooks with accessory tooth or teeth above the main fang, 1 accessory tooth (bidentate), secondary tooth closely applied to the main fang, about 45º. Shaft of neuropodial hooded hooks of constant thickness, lacking a constriction. Neuropodial sabre chaetae present, in ventral-most positions, first on chaetiger(s) 11. Neuropodial spines absent. Embedded bunches of notopodial needle chaetae absent. Pygidium with 4 broad, flattened anal cirri, ventral and ventrolateral, with boad dorsal gap; cirri with fine bacillary glands; anus terminal.

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, J.A. 1984. Four new species of Spionidae (Polychaeta) from New Zealand, with comments on a syntype of Spio aequalis Ehlers from Chatham Island. Proceedings of the Biological Society of Washington 97: 148-159.