| Abstract: | Bathymetric distribution, abundance, substrate choice and gametogenesis have been investigated in two species of deep-sea actiniarians found in the northeast Atlantic Ocean. Phelliactis hertwigi occurs at 719–1448m in the Porcupine Seabight, usually encloses a bolus of sediment within its highly concave pedal disc (79.7%), and has abundances of up to 14.5 individuals 1000m−2. Phelliactis robusta occurs at 1600–2173m in the Porcupine Seabight, but extends deeper in the Bay of Biscay. In areas of soft sediment it is associated strongly with clinker (92.7%) and attains densities of 2.9 individuals 1000m−2.Both species are dioecious. Their sperm appear similar to those of the related intertidal Calliactis spp. Previtellogenesis and vitellogenesis of the oocytes have been defined by ultrastructural and histochemical studies. In P. hertwigi mature oocytes measure up to 180μm, and to 210μm in P. robusta. In P. hertwigi oogenesis takes 8–9 months, with spawning in October/November, whereas in the deeper-living P. robusta oogenesis occupies 15 to 19 months and spawning occurs in April/ May. Evidence is produced to suggest that these two contrasting cycles are related to the rate and seasonality of deposition of organic matter to the deep-sea floor. |
