Observations on the bivalves Montacuta substriata and M. ferruginosa 'commensals' with spatangoids

Gage, J. (1966) Observations on the bivalves Montacuta substriata and M. ferruginosa 'commensals' with spatangoids. Journal of the Marine Biological Association of the United Kingdom, 46 (1). pp. 49-70.

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Abstract

Field and laboratory observations were made of the erycinacean bivalves Montacuta substriata and M.ferruginosa, which are usually considered as'commensals', respectively, with the burrowing spatangoids Spatangus purpureus and Echinocardium cordatum. These species were obtained mainly from the Plymouth area, where M. substriata was also found with E. fiavescens and E. pennatifidum, and also very occasionally with E. cordatum. Similarly, M.ferruginosa was also found with S. purpureus, E. fiavescens and E. pennatifidum. This indicated that the associations are not as specific as had been thought.Associated examples of M. ferruginosa were observed in situ both by digging'host' urchins at E.L.W.S. and, together with M. substriata, on urchins dredged offshore. Their incidence and the total complement with each urchin was noted. Direct observations were also made of M. substriata and M. ferruginosa associated with different spatangoids burrowing in tanks in the laboratory. These indicated that the associations are not permanent, and that they can change position on the 'host' if attached by a byssus, or re-associate with another individual. They could also remain free-living in the substratum for long periods. The presence of a ferruginous layer-most noticeable and characteristic of M. ferruginosa with E. cordatum-was correlated with the nature of the sediment. The observations also indicated that the' tangles' of byssal threads secreted by M. ferruginosa function in aggregating the bivalves together in the burrow as well as in attachment of the young bivalves to the urchin. The observed behaviour of the bivalves indicated that a behavioural mechanism operates in the maintenance of their associations with spatangoids. Speculations are offered on the nature of some components of this behaviour.

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