ANNUAL GONADAL VARIATION IN SEA URCHINS OF THE ORDERS ECHINOTHURIOIDA AND ECHINOIDA

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Abstract
The echinothurioid sea urchins Asthenosoma ijimai and Araeosoma owstoni were collected throughout the year. Their gonads were studied histologically by light microscopy and compared with those of some species of the order Echinoida. The ovaries contained degenerating and large developing oocytes throughout the year, showing that, unlike species of the order Echinoida so far studied, the Echinothurioid sea urchins lack the so-called resting state in which the ovaries contain only oogonial clusters. In the testes of this species, differentiation of spermatocytes into more advanced stages of male germinal cells appears to be blocked until at least 5 mo. before spawning. Spermatids appeared 3 mo. before spawning and spermatozoa at least 1 mo. before. Factors involved in differences in annual gonadal variation between the sea urchins of the orders Echinoida and Echinothurioida are discussed.