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

The echiuran worm Thalassema thalassemum (Echiura: Echiuridae), is a deposit-feeder which uses its proboscis to collect sediment particles for ingestion. The proboscis is highly extensible and is used with dorsal surface downwards to skim particles from the sediment surface. Alternatively, 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 used in combination and collected material is moved back along the proboscis, the edges of which are rolled to form a closed tube. Burrows appear to be U-shaped with one predominantly inhalant and one exhalant opening. Faecal pellets are periodically ejected forming small mounds around 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 could make a significant contribution to macrofaunal bioturbation.