OBSERVATIONS ON THE BEHAVIOR OF THALASSEMA-THALASSEMUM (ECHIURA, ECHIURIDAE)

The echiuran worm Thalassema thalassemum (Echiura: Echiuridae), is a d eposit-feeder which uses its proboscis to collect sediment particles f or ingestion. The proboscis is highly extensible and is used with dors al surface downwards to skim particles from the sediment surface. Alte rnatively, the distal portion of the proboscis is arched over and the ventral surface of the tip is held against the sediment surface where ciliary movement facilitates particle collection. These methods are us ed in combination and collected material is moved back along the probo scis, the edges of which are rolled to form a closed tube. Burrows app ear to be U-shaped with one predominantly inhalant and one exhalant op ening. Faecal pellets are periodically ejected forming small mounds ar ound exhalant openings and mean rates of 1.83 and 2.80 g dry wt d(-1) were measured suggesting that, in sufficient densities, this species c ould make a significant contribution to macrofaunal bioturbation.