1976/01/01 by Peter W. Skelton · 3 citations
Agricultural and Biological Sciences · #Mollusks and Parasites Studies
paper · doi:10.1111/j.1502-3931.1976.tb00953.x
The hippuritid shell consists of a small operculiform left valve capping a larger cylindrico-conical valve. There are three shell layers: (1) An outer calcitic fibrillar prismatic layer. (2) A crossed-lamellar aragonitic middle layer. (3) A complex crossed-lamellar aragonitic innet layer. There are also traces of myostracal prismatic aragonite which mark former adductor positions, the attachment site of the body mass, which hung largely from within the left valve, and the pallial curtain of the right valve alone. It =ms that water was drawn through the pores on the outer surface of the left valve, into the radial canals which lie within its outer layer. It then flowed outwards from the canal apertures, passing over the broad and radially crenulated right mantle margin, whereon food particles were trapped. The particles were sorted and passed inwards anterieventrally onto the ctenidia and/or palps, which carried them to the mouth. Faeces were ejected via the dorsalmost of two oscules in the left valve, and pseudofaeces via the ventralmost oscule. The form of the adductor muscles and their orientations upon myophores projecting from the left valve suggest immovable valves only separated by a minute gape. These modifications complemented the atrophy of the normal bivalve internal feeding and respiratory current system. La coquille des Hippuritidae comprend we valve gauche operculiforme et une valve droite cylindro-conique. Le test est forme de trois couches: 1. Une couche externe constituee de fibres prismatiques de calcite; 2. Une couche moyenne aragonitique a structure lamellaire entrecroisee; 3. Une couche interne aragonitique a structure lamellaire entrecroisee com-plexe. Les zones d'insertion des muscles adducteurs, de la masse viscerale et des muscles palleaux, montrent en outre des traces de primes myostracaux d'aragonite. Les courants d'eau inhalants peneraient par les pores de la valve gauche et cheminaient dans les canaux radiaux qui parcourent la couche externe, pour deboucher a la cornissure des deux valves; ou les particules alimentaires etaient retenues. Les particules etaient triees et acheminees vers la region antero-ventrale de la cavite generale en direction des branchieslou des palpes et de h bouche. Les feces etaient rejetes par l'oscule dorsal de la valve gauche, les pseudo-faxs par l'oscule ventral. La forme courte des muscles adducteurs et leur orientation sur les apophyses myophores de la valve gauche suggere que les valves etaient immobiles et ne laissaient entre elles qu'un faible intervalle. Ces modifications vont de pair avec I'atrophie du systeme digestif et respiratoire.