Samples of deep-sea asteroids were collected in a time-series from a station at 2200m in the northern Rockall Trough. These were supplemented by specimens from less regular samplings at other stations. Gametogenic cycles were analysed by determination of gonad and gut caecum indices and oocyte size-frequency distributions and by observations of histology, histochemistry and ultrastructure. Of 15 species examined, 13 showed no reproductive periodicity. Oocytes ranging from prey itellogenic to maximum size are always present in the mature ovary. Size frequency data show a pattern of continuous growth of oocytes with no synchrony between individuals. Fecundity is low and mature oocytes large (c. 1000pm diameter) and yolky, suggesting direct development. Spermatogenesis follows a similar pattern in all these species: mature males are always ripe, ready to shed sperm at any chance encounter with a female. Two species, Plutonaster bifrons and Dytaster insignis, show a contrasting reproductive strategy. They are highly fecund, producing many small (< 120pm) eggs, suggesting planktotrophic larval development. Oocyte size-frequency distributions of P. bifron s indicate a seasonal cycle of gametogenesis with synchrony between individuals and spawning from March to June. Fine structural examination reveals a common structure for somatic portions of the gonads. In seasonally-breeding, species oocytes begin development while unspawned ripe oocytes are being resorbed. Oocyte growth is synchronous and yolk formation begins at c - 40pm diameter. In all a seasonally-breeding species pre-vitellogenic oocytes are very similar. Vitellogenesis begins in the oocyte periphery in different-sized oocytes in the various species. There are differences in the form and numbers of ovarian accessory cells and also in the nature of processes involved in the destruction of excess small oocytes or in the removal of unspawned eggs. Resorption involves phagocytosis or internal degeneration or both. These differences are most marked at family level, suggesting that this strategy has been derived independently in each family. The fine structure of the testes conforms to the basic pattern for asteroids.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:638398 |
| Date | January 1983 |
| Creators | Pain, S. L. |
| Publisher | Swansea University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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