The prostomium is a narrow ridge, often
referred to as the prostomial lobe, and the peristomium is
reduced. Antennae are absent, and peristomial paired grooved
palps are located at the corners of the mouth. Nuchal organs
are paired ciliated ridges lateral to the prostomium. The
longitudinal muscles are arranged in bundles. The first
segments are fused to form the branchial membrane (or
cephalic hood). Parapodia are biramous and
poorly developed. All notopodia and
neuropodia are short, and are distally truncate or tapering.
Dorsal and ventral cirri are absent. Dorsal segmental
branchiae are present and arise from the cephalic hood. Lateral organs and dorsal cirrus organs have not been observed. Papillae of a characteristic structure are present,
often especially dense and long around chaetae. An eversible ventral buccal organ is present
and the gut is looped. A gular membrane is present.
Segmental organs are present as mixonephridia; the
anteriormost pair is excretory and the more posterior ones
function as gonoducts. The circulatory system is closed, and a
heart body is present. Aciculae are absent. Chaetae are present
as falcate compound falcigers and variously ornamented
capillaries. The relatively thick, distally blunt
chaetae present in many species of flabelligerids have been
referred to as spines and as modified capillaries.
The above description is based on Hutchings (2000), which in turn is based on Fauchald & Rouse (1997).
Identification tips
Recognising the family
Both Flabelligeridae and Fauveliopsidae have interramal papillae, but fauveliopsids have spines in both notopodia and neuropodia whereas flabelligerids only have spines in neuropodia. Flabelligerids are frequently collected in benthic samples, especially in poorly-sorted sediments, whereas fauveliopsids are quite uncommon.
Distinguishing species
Complete individuals are required for identification, and it is often difficult to see the grooved palps which are often contracted and hidden by the cephalic cage. Examination of live specimens helps in the interpretation of the various head structures.
