The short prostomium is truncated anteriorly, and the peristomium is reduced to lips around the mouth,
although this interpretation is questioned by Rouse &
Pleijel (2001) who accept that the peristomium forms a distinct annulus,
based on larval developmental studies and scanning electron micrographs of adults. Antennae and palps are absent. Paired nuchal
pits are present. The longitudinal
muscles are grouped in bundles and
segmentation is present. The first segment is similar to other
chaetigers, and tentacular cirri, parapodia and parapodial cirri
are lacking. Paired, filiform, dorsal branchiae are present in
some taxa. Epidermal papillae, pygidial cirri and lateral
organs are not present; dorsal cirrus organs have not been
observed and are probably lacking. An eversible ventral
buccal organ is present and the gut is a straight tube. A gular membrane is absent. The segmental
organs are mixonephridia; there is only one excretory pair,
and gametes exit through the more posterior ducts. The circulatory system is closed, and a heart
body is present. Aciculae are absent. Capillary chaetae are
present in the Raphidrilinae; other chaetae are distally dentate
hooks. The chaetae have been referred to as proteinaceous; if verified, this state would be unique among the polychaetes.
The above description is based on Hutchings (2000), which in turn is based on Fauchald & Rouse (1997).
Identification tips
Recognising the family
The Ctenodrilidae can be easily recognised by the multi toothed chaetal hooks which are unique to the family. Ctenodrilidae have grub-shaped body not divided into regions, chaetae include hooks and pygidium comprising a simple ring or cone. Most ctenodrilid species lack all appendages but one group of Ctenodrilidae do possess filiform branchiae. They are small sedentary worms, 3-20 mm in length with varying number of segments. This family was originally classified with the Cirratulidae.
Distinguishing species
Ctenodrilid species are characterised by the chaetae which include capillaries, pectinate to coarsely serrated forms and hooks which are distinctly dentate distally.
