The Terebellidae have a reduced prostomium which is fused
along its posterior edge to the peristomium. The peristomium
is also fused with the first anterior body segment, and projects
forward beneath the prostomium as an extended upper lip.
Palps are usually present as numerous (buccal) tentacles,
which emerge at the point of fusion between the peristomium
and the prostomium. Nuchal organs are usually
present, and the longitudinal muscles form bands.
Segmentation is typically distinct. The first segment, fused to
the head, has no parapodia or chaetae. Parapodia are typically
biramous; they are lacking in some species (for example,
Hauchiella species). The notopodia are cylindrical, either
slender or truncate, and are often restricted to the anterior
segments of the body. Neuropodia are present as tori or may
be absent. Branchiae, if present, are dorsal and situated only
on a few anterior segments. Epidermal papillae and pygidial
cirri are absent. There is a non-eversible ventral buccal organ.
Mixonephridia are present in each segment;
anteriorly, these ones function as excretory organs and the
posterior ones are used as gonoducts. Chaetae are present as a
variety of ornamented capillaries and uncini;
they are rarely absent. Aciculae are absent.
This description, taken from Hutchings (2000) is in turn based on that of Fauchald & Rouse (1997).
Identification tips
Recognising the family
Terebellids are most likely to be confused with Ampharetidae and Trichobranchidae. The three families are closely related and are best separated using the key to families. Sometimes members of the Cirratulidae are misidentified as Terebellidae by inexperienced sorters, because the masses of buccal tentacles of terebellids may appear superficially similar to the branchiae of cirratulids. However, cirratulids (which are often bright orange in life) have branchiae occurring on most segments, whereas of course the buccal tentacles of terebellids all arise from the buccal cavity.
Terebellids are common in soft bottom communities as well as on rocky reefs.
Distinguishing species
The presence or absence of branchiae and their structure are important characters, as is the segment on which the notopodia and neuropodia commence. Structure and arrangement of the chaetae and their distribution along the body is also important. In genera with lateral lobes, their shape and distribution is important at the species level. Most terebellids occur in muddy tubes or ones constructed of sand grains, but some genera live naked in the sediment.
