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Abstract
The Ophiocomidae, a species-rich family of ophiuroid echinoderms, encompasses a range of developmental modes. We investigated the reproductive biology of four species: Ophiocoma dentata with planktotrophic development and a small egg, and three species with lecithotrophic development and eggs that differ in size (Clarkcoma pulchra, C. canaliculata and O. endeani). Reproduction was investigated by in situ observations, spawning trials and/or gonad histology. Gonad histology of O. dentata from the Northern and Southern Great Barrier Reef indicated that spawning occurs for six to seven months from January to June/July. Gonads of O. endeani, an endemic of subtropical New South Wales, were mature from December to February. In situ observations of two populations of C. pulchra and C. canaliculata in the Sydney region indicated they spawn from December to May. Egg morphology showed modifications in oogenesis associated with the evolution of a large egg, particularly in enhanced deposition of lipid. The eggs of O. dentata, a planktotrophic developer, contained densely packed, strong periodic acid Schiff's + yolk granules and were negatively buoyant. The eggs of species with lecithotrophic development were dominated by lipid droplets indicating that the evolutionary modification of oogenesis resulted in differences in yolk granule and lipid droplet distribution potentially influenced by selection for egg buoyancy.
Acknowledgements
We thank the staff of the Lizard Island Research Station, a facility of the Australian Museum and the staff of the OTI Research Station, a facility of the University of Sydney. This work was supported by a scholarship from the University of Sydney (IF) and the Australian Research Council (MB). We thank Ben Mos for assistance with specimen collection.