Pseudatherospio

Prostomium blunt, anteriorly truncate or rounded, anterior margin bifid, with anterior margin indented. Lateral horns absent. Caruncle present. Occipital antenna present. Nuchal organ short, at most one segment long. Eyes 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 and partially or wholly fused with notopodial lamellae (on some or all chaetigers) (on chaetigers 7–16; free otherwise), 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 (but dorsal transverse ciliary bands present). 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 below the main fang, 1 accessory tooth (bidentate). Shaft of neuropodial hooded hooks of constant thickness, lacking a constriction. Neuropodial sabre chaetae absent. Neuropodial spines present, aristate (and a subterminal fringe of hairs). Embedded bunches of notopodial needle chaetae absent. Pygidium unknown.

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:
Lovell, LL. 1994. Pseudatherospio fauchaldi, a new genus and species of Spionidae (Polychaeta, Annelida) from southern California, USA. Mèmoires du Musèum National d'Histoire Naturelle 162, 237-241.