UNDERWATER TELEVISION OBSERVATIONS OF SURFACE-ACTIVITY OF THE ECHIURAN WORM MAXMUELLERIA-LANKESTERI (ECHIURA, BONELLIIDAE)

Surface activity of the deep-burrowing echiuran Maxmuelleria lankesteri (Herdman) was observed in Loch Sween, Argyll (Scotland, UK) using underwater television. Activity, consisting of proboscis emergence and sediment venting, was observed in all seasons. Proboscis emergence was strictly nocturnal, occurring on average on one night in two. Emergence occurred at irregular intervals during the night, with no consistent rhythmicity. Feeding extensions of the proboscis usually lasted about 10 min, but were often curtailed by accidental contact with ophiuroids or other epifauna. The extending proboscis skims off the top layer of sediment, then rapidly pulls the collected material into the burrow. Animals showed a capacity to select material from particular areas within the feeding radius. The feeding strategy may be to accumulate several loads of sediment in the burrow, then selectively ingest material over the following day. Large volumes of sediment were often vented from burrows, either in a fine suspension, or in a denser slurry. Venting could occur by day or night, successive pulses of material being expelled over periods of up to 19 min. The dense slurry may consist of surface material collected but not ingested. Some proportion of the animal's faeces is also expelled. Animals were seen to expel plumes of sediment in response to disturbance of the mound. In view of the observed capacity of M. lankesteri to move large volumes of sediment (provisional estimates suggest up to 30-40 cm3 day-1) into and out of its burrow, we consider the animal to be a potentially significant bioturbator.