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Trichobranchidae: Trichobranchus gooreekis

The Trichobranchidae is characterised by the fusion of the prostomium to the peristomium along the anterior margin of the prostomium. The peristomium forms extended lips; the upper lip may be expanded to form lateral lobes and the lower lip may be greatly expanded to form a ridged, conical eversible proboscis which may be completely retracted. The palps are represented by multiple grooved buccal tentacles, which cannot be retracted into the mouth. Nuchal organs are present in Trichobranchus species, but not in Terebellides species; the condition is unknown for other genera. Segmentation is distinct. The first segment is fused to the head and lacks parapodia and chaetae. The body is divided into two regions: the thorax, bearing notochaetae and neurochaetae, and the abdomen, with neurochaetae only. Branchiae occur dorsally on segments 2 to 4; the filaments may be filiform, foliaceous, rosette-like in two or three groups or may form a single large branchia bearing two to five lamellate lobes. Ventral glandular pads are absent. The pygidium is smooth or lobed and small cirri may be present. Lateral organs and dorsal cirrus organs have not been observed. There is a non-eversible ventral buccal organ and the gut is looped. A gular membrane is present. Nephridia are present as metanephridia; the relation to coelomostomes has not been documented. The anteriormost pair of nephridia are excretory in function; the posterior ones presumably act as gonoducts. The circulatory system is closed and a heart body is present. Aciculae are absent; other chaetae are variously ornamented capillaries and uncini which may be acicular, or avicular with short or long shafts.

The above description is taken from Hutchings (2000), which in turn is based on Fauchald & Rouse (1997).

Identification tips

Recognising the family
Trichobranchids are often confused with terebellids and ampharetids, although the branchiae are either single filaments arranged segmentally or composed of partially fused lamellate lobes, such branchiae and arrangement are not found in these other families. Unlike these other families thoracic neurochaetae are different to abdominal ones, they are long handled hooks whereas abdominal ones are avicular short handled uncini. Trichobranchids have a fixed number of thoracic segments, and a variable number of abdominal segments with neuropodia only. Trichobranchids tend to have short compact bodies and Artacamella has an eversible proboscis.

Distinguishing species
Characters used to distinguish species include the form and orientation of the chaetae, branchial structure, and the structure of the head (peristomium and prostomium).


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