Otolithic apparatus in Black Sea elasmobranchs

Abstract

Using light, transmission and scanning electron microscopy, and morphometry, we examined the otolithic organs of 25 Raja clavata (35–93 cm), 12 Dasyatis pastinaca (34–50 cm), and two Squalus acanthias specimens (100 and 145 cm). In D. pastinaca all three otolithic membranes merge into one another, and the otolithic apparatus as a whole is relatively poorly developed. In R. clavata and S. acanthias the large saccular otolithic membrane and the small lagenar otolithic membrane are continuous. The mass of the otolithic membrane and the length of the animal are power related. The otoconia of rays tend to be lemon shaped or spherical. The dogfish has large, cuboidal (parallelepiped-shaped) endogenous otoconia, exogenous sand grains, and crystal-containing globules. The size of the endogenous otoconia does not depend on the size of the animals. No specialized zones were found in rays either on the surface or inside the otolithic membranes containing otoconia of one type or size. The data indicate that the mass of the otolithic apparatus in rays increases on account of the formation of new otoconia. The otolithic apparatus of the dogfish can also increase in mass by addition of small grains of sand, which enter the labyrinth and are incorporated into the otolithic membrane.