838. LIFE HABIT AND RELATIVE GROWTH OF SOME LAQUEID BRACHIOPODS FROM JAPAN

Abstract

Japanese Cenozoic laqueid brachiopods generally show two allometric trends. One is the ontogenetic increase in valve convexity versus valve length, and the other is the ontogenetic decrease in valve width versus valve length. To examine the causation of these morphologic changes, the general morphology, life habit, and allometric relationships of some metric characters were investigated in the Recent samples of Laqueus rubellus (Sowerby). The following are three explanations for the relative increase of shell convexity : 1) efficient secretion of shell material, 2) strengthening the shells, and 3) providing larger space for adult gonad. Among them, the third explanation seems most appropriate at least in L. rubellus, because of a diphasic allometric relationship between valve convexity and valve length : while valve convexity is positively allometric to valve length in adults, they are isometrically related in juveniles.