Boccardia acus (Rainer, 1973)

Prostomium blunt, anteriorly truncate or rounded, anterior margin bifid, with anterior margin indented. Lateral horns absent. Caruncle present, continuing back to chaetiger 2, fused with dorsum. Occipital antenna absent. Nuchal organ short, at most one segment long. Eyes present; 4 eyes. Palps simple, lacking basal sheath. Body translucent in live specimens; orange or green gut apparent through body wall; blood vessels in gills, palps and dorsum clearly visible. Dorsal ridge connecting bases of branchiae on chaetiger 1 absent. Prominent dorsal collar on setiger 2 absent. Dorsal branchiae present, first present on chaetiger 2. Dorsal branchiae absent from many median and posterior chaetigers, last present on chaetiger 22. Dorsal branchiae interrupted, (absent) on chaetigers 5. Dorsal branchiae free and separate from notopodial lamellae throughout, all simple. First branchiae without process at base on anterior face. Branchia length increases grandually to just over half body width in midbranchial region, decreases rapidly over last few pairs. 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 highly modified, enlarged and with specialised chaetae, with two types of modified spine present; simple, curved or subdistally inflated spines present; spines with subdistal tooth or flange absent; pennoned spines, with strongly asymmetrical tips absent; spines with flattened or cup-shaped tip absent; spines with terminal or subterminal bristles present; companion chaetae absent. Posterior modified notochaetae present, on chaetigers 50–55. Notopodial hooded hooks absent. Neurochaetae of chaetiger 1 simple capillaries similar to those of subsequent chaetigers. Neuropodial hooded hooks present, first present on chaetiger 8. 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 absent. Neuropodial spines absent. Embedded bunches of notopodial needle chaetae absent. Pygidium a broadly flaring collar, open dorsally.

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:
Rainer, S.F. 1973. Polydora and related genera (Polychaeta: Spionidae) from Otago waters. Journal the Royal Society of New Zealand 3: 545-564. http://www.annelida.net/nz/Polychaeta/Family/Spionidae/boccardia-acus.htm