INTERNAL SHELL STRUCTURE AND GROWTH LINES IN THE SHELL OF THE ABALONE, HALIOTIS-MIDAE

The internal shell structure of the South African abalone, Haliotis mi dae, was studied using scanning electron microscopy. Growth lines were counted. The shell consists of the periostracum, prismatic, and nacre ous layers. The outer, noncalcified periostracum consists of a single, honeycombed layer. Calcified layers include a simple prismatic and a nacreous layer, the latter being composed of sheet nacre, which is unc haracteristic of gastropods. Growth lines were deposited in the nacreo us layer of animals, even under controlled laboratory conditions. In a nimals of known age, three lines were deposited in the first year and one in each subsequent year. Rate of deposition of lines was not relat ed to diet, temperature, or photoperiod.