Adaptational Significance of the Patterns of Ophiuroid Development

Abstract

There is only limited information on ophiuroid developmental patterns, larvae being known for only 4% of the 2000 living ophiuroids. Three modes of development are distinguished (planktotrophic, direct, abbreviated) on the basis of egg size and number, larval form and life span, and post-larval size. This generalization is applied to an analysis of the larval form(s) of deep-sea ophiuroids and the ancestral ophiuroid larva. Quantitative information on rate of development and reproductive period, which has been lacking for viviparous ophiuroids, is presented for Axiognathus ( = Amphipholis) squamatus on the basis of original size-frequency data. Reproduction is seasonal in the population studied and development to metamorphosis takes no longer than for planktotrophic species though the brooding period ranges from 3 to 7 months. Additional data indicate post-larvae of planktotrophic species have fewer arm segments than newly-hatched viviparous young, supporting the hypothesis that large size of juveniles is characteristic and selectively advantageous for viviparous ophiuroids.