In samples from 4095 m and 398 m in the Porcupine Seabight foraminiferans constitute 58.4 - 79.3~ of the total~meiofauna. Nematodes followed by harpacticoid copepods are the most abundant meiofaunal metazoan taxa. Foraminiferal densities (967 - 1331 individuals 10 cm-2 ) and diversities (68 - 95 species; Shannon- Wiener index = 3.21 - 4.15) are higher than recorded in most previous studies. This is attributed to the detailed sorting procedure adopted which also provides information on the sizestructure and vertical distribution of foraminiferal assemblages in the top 5 cm of sediment. Most specimens were smaller than 150 ~m and some were infaunal. Komokiaceans only occurred at the deeper site. Allogromiids, hormosinaceans and unilocular agglutinating forms had increased relative abundances at the deeper site while the Rotaliina were relativelY,less common. The composition of these assemblages is discussed in relation to changes in the sediment structure, as observed in resin impregnated sediment cores. The morphology and fine structure of two large agglutinating foraminiferans, Rhizammina al&aeformis Brady and Pelosina aff. aborescens Pearcy, was examined using light microscopy, SEM and TEM. In R. al&aeformis the test is a long, branching tube which sometimes forms a tangled mass on the sediment surface. It contains a protoplasmic strand and extracellular mass of stercomata. The protoplasm is deeply invaginated to produce a system of labyrinthine spaces communicating with the tube lumen and possibly providing sites for extracellular digestion. The stercomata are enveloped in an organic sheet-like system and contain clay minerals. In f. aff. arborescens the tree-like test projects above the sediment surface. Protoplasm occurs in the central lumen. in fine branching canals which ramify through the thick. muddy. test wall. as well as in the distal branching complex. In TEM the protoplasm has a highly vacuolated appearance. There are no stercomata. Differences between the two species seem to reflect different feeding strategies; R. alKaeform1s 1s probably a deposit feeder and f. aff. arbor esc ens a suspension feeder.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:383415 |
| Date | January 1988 |
| Creators | Cartwright, N. G. |
| Publisher | University of Reading |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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