Experiments with the behaviour of the bivalves Montacuta substriata and M. ferruginosa, ‘commensals’ with spatangoids

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Abstract
The behaviour involved in the maintenance of the ‘commensal’ associations of Montacuta substriata and M. ferruginosa with spatangoids was investigated experimentally.Both species are highly mobile when isolated from the ‘host’, and this activity was recorded through their mucous trails on glass plates, and photographically with a repetitive electronic flash system. Their responses were analysed mainly in a trough apparatus with a slow flow of water. The behaviour was resolved into responses to factors normally present in their environment. These included both gravity and water currents and a chemical influence from the ‘host’ spatangoid. M. substriata showed a marked negative geotaxis, while M. ferruginosa showed a similar response but of opposite sign. Pedal activity was stimulated as a kinesis to an unknown chemical ‘attractant’ from the urchin. The bivalves showed no specificity in this response since it was shown by both species to any of the spatangoids tested, regardless of the urchin species from which they were taken.