The Determination of Relative Growth in Crustacea

Relative growth in Crustacea is generally in accordance with the simple allometry rule, y = Bxα. The regulation of growth at each ecdysis is such as to result in the attainment, where possible, of the proportions dictated by this rule. Growth proceeds as a series of phases, each composed of from one to several instars. Within each phase there is simple allometric growth, but both the levels of allometry and the size of the variables often change at the transition between phases. These transition changes may be minimal, but they can be so prominent as to result in an obvious critical moult or metamorphosis. In Brachyura there is a consistent pattern of phases in the later post-larval life, the critical moults separating the final three phases being known as the pre-puberty and puberty moults respectively. There can be polymorphism of the terminal mature phase. The critical moults do not necessarily appear to have fixed positions in the sequence of post-larval instars.