In simple choice experiments Protodrilus symbioticus Giard, an interstitial archiannelid, was shown to prefer the sand from its habitat in the natural state to the same sand altered by various physical or chemical treatments. The attractiveness of a sand was measured as the ratio of the number of Protodrilus entering the experimentally treated sand to the number entering the natural sand in simple or multiple choice experiments.

The attractiveness of natural sand to P. symbioticus could be destroyed almost completely by acid cleaning, by heating in water above 50° C or by drying at any temperature.

Treating attractive sand with formalin or cetyltrimethylammonium bromide rendered it about half as attractive as before treatment. Heating natural sand in water to 40°C and keeping it in fresh water for 18 h had no effect on the attractiveness. Sands that have been made unattractive by acid cleaning or drying can be restored to an attractive state by soaking in sea water. Typically acidcleaned sands recovered up to half and dried sands almost the whole of the attractiveness.

Inoculation of naturally occurring sand bacteria to highly unattractive acid-cleaned sand restores the attractiveness completely. Autoclaved sand to which a culture of Phaeodactylum had been added was preferred to sand treated with cultures of Dunaniella and Chlorella. An ordinary culture of Phaeodactylum contaminated by bacteria restored the attractiveness to autoclaved sands more effectively than a bacteria-free culture.

Sands restored by inocula of natural sand bacteria, soil bacteria and Pseudomonas sp. were preferred to those treated with Corynebacterium erythogenes, Flavobacterium sp. and Serratia marinorubra and these were preferred to control sands kept in sterile sea water.