BODY GROWTH VERSUS SHELL GROWTH IN BALANUS IMPROVISUS

Abstract

Measurements of portions of exuviae (maxillae and mandibles) of Balanus improvisus, plus comparison of mouth part size and body size of living barnacles taken from the harbor, show that the maxillae of the shed exoskeleton may be used as an index to body size increase at molting. Measurements of 20 barnacles reared in the laboratory during the first 20 consecutive molting periods indicate that body growth does not necessarily accompany ecdysis. The increase in size of the maxillae at molting is variable and tends to become smaller as the size of the barnacle increases. Growth of the calcareous shell occurs even when there is no increase in maxillae size. The original ratio between body size and shell size is not maintained as growth continues. The result of this changing ratio, a large shell enclosing a relatively smaller body, provides a mantle cavity of sufficient size in the adult to accommodate the developing egg lamellae.