PREEMBRYONIC AND POSTEMBRYONIC DEVELOPMENT, GROWTH AND TURNOVER OF OLFACTORY RECEPTOR NEURONS IN CRAYFISH ANTENNULES

The antennules of the crayfish Cherax destructor can first be observed as antero-laterally located lobes in embryos that have reached the 50 % stage of development. Clusters of cells that are probably the olfac tory receptor neurones (ORNs) appear at the distal end of these lobes, which later differentiate into the lateral flagella of the antennules . New clusters of ORNs and segments are added at the proximal end of t he lateral flagellum throughout the postembryonic stages and well into the juvenile adult stage. From a comparison of the exuvia and the new ly emerged flagella in animals over a wide range of sizes, we conclude that, once the animals reach a certain size (approximately 7 mm carap ace length), the most distal, and oldest, segments of the antennule ar e shed. Growth occurs from the proximal end of the flagellum, and the addition of new ORNs is the result of a delayed differentiation of the flagellar segments that takes place at the proximal end of the chemor eceptor array, about halfway along the flagellum.