On the Habits and Adaptations ofAloidis (Corbula) Gibba

Abstract

1.Aloidis (Corbula) gibbais a eulamellibranch specialized for life in muddy gravel substrata to depths of up to about 80 fathoms.2. The shell is asymmetrical, the margin of the smaller, left valve being uncalcified and so fitting within the marginal region of the right valve. A possible manner in which this asymmetry is produced by the differential secretory activities of the two mantle edges is discussed.3. The marginal periostracum of the left valve has strengthening calcined regions posteriorly, probably to protect the siphons when extruded.4. The external ligament is reduced and the resilium condensed, possibly permitting some antero-posterior rocking of the shell valves when the adductors contract.5. The process of burrowing is described; on its completion the animal is anchored by a single byssus thread.6. The siphons are very short, the tentacles of the siphonal sheath lying on the surface of the substratum. The inhalant siphon is wide and relatively insensitive; it draws in much bottom material. The exhalant siphon is tubular and very sensitive. It is controlled by two paired bands of muscle.7. The great quantities of pseudo-faeces which accumulate are expelled by periodical contractions of the 'quick' portions of the adductor muscles, the asymmetry of the shell valves causing great reduction in the size of the inhalant chamber. The foot may also assist in clearing the chamber. 8. The large ctenidia create a very powerful current; they are adapted for dealing with large amounts of sediment by means of specialized terminal, guarding and cirrus-like cilia. Control of 'pumping' is primarily by means of the exhalant siphon.9. The stomach is large in correlation with the great amounts of inorganic material carried in with the food.