MICROSTRUCTURE AND ULTRASTRUCTURE OF THE RADULA OF HALIOTIS DIVERSICOLOR

In order to investigate the structural and developmental changes in the radula,analyse the relation between radula morphology and digestive physiology in healthy abalone,we examine the radula of Haliotis diversicolor by light,scanning and transmission electron microscopes.Radula formula of the large juvenile abalones and mature abalones is ∞+5+1+5+∞,namely,Radula is made up of central teeth,lateral teeth and marginal teeth.There are one transverse row of central teeth and five pairs of lateral teeth(L1,L2,L3,L4 and L5) in the radula.The amount of marginal teeth is variable.The sizes of L4 and L5 teeth of juvenile and adult H.diversicolor were much smaller than L3 teeth.The overall length of radula increased linearly with abalone shell length,reflecting increases in the gap between adjacent rows of teeth,the length of teeth,and the number of transverse rows of radula teeth.The width of the radula also increased linearly as the ablone grew.This increase in width was caused mainly by the increase in width of the individual teeth,delayed addition of L3-L5,steady increase in number of marginals.The sizes of L4 and L5 teeth of juvenile and adult H.diversicolor were much smaller than L3 teeth.Mature abalones have many more marginal teeth than large juvenile abalones,and the radula of mature abalones is longer and wider than that of the large juvenile abalones.The serrations on teeth were worn as abalones grew,first on central teeth,and later on L1 and L2,finally on L3-L5,nearly all the serrations disappeared at last.Further studies on the detailed functions of the different types of abalone radula teeth(central teeth,L1-5 and marginal teeth),the way they are used during feeding,and their hardness and flexibility during development are needed to more fully understand about the transitions in feeding and the food sources of abalone throughout their life stages.The present study describes morphological developments from large juvenile to mature abalones in Haliotis diversicolor that are remarkably similar to those observed in Haliotis discus hannai Ino,Haliotis iris,Haliotis rubra,Haliotis diversicolor aquatilis,which are ecologically similar but not closely related.Study of radula development in a wider range of abalone will provide an interesting comparison of the influence of genetics and ecology on the evolution of abalone radulae.