Taxonomic and ecological studies on Antarctic octocorals of the genus Thouarella (Octocorallia: primnoidae)
Amongst the primnoids collected by the Brazilian Antarctic Expeditions, the genus Thouarella is the most abundant and Thouarella variabilis the dominant species. Thouarella variabilis shows in a notable range of variation of characters. Some of the characters which have been applied in diagnosing th...
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| Format: | Thesis |
| Language: | English |
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University of Southampton
1993
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| Online Access: | https://eprints.soton.ac.uk/462424/ https://eprints.soton.ac.uk/462424/1/422364.pdf |
| Summary: | Amongst the primnoids collected by the Brazilian Antarctic Expeditions, the genus Thouarella is the most abundant and Thouarella variabilis the dominant species. Thouarella variabilis shows in a notable range of variation of characters. Some of the characters which have been applied in diagnosing this species are inconsistent and should be used with caution. An evaluation of the validity of these characters as reliable descriptors for this species is presented. An investigation of the colony morphology; structure, formation and function of sclerite; growth and estimates of age; internal morphology and reproductive biology of Th. variabilis was undertaken. The results of the studies on reproductive biology, showed that the colonies of Th. variabilis are gonochoric brooders. The polyp fecundity is low with only one larva being released per female polyp at a time. The presence of oocytes in different stages of development within the same polyp suggests a two year cycle of oogenesis. The developing oocyte grows to a maximum size of 660 μm. A non-feeding, non-pelagic leithotrophic planula larva is retained within the polyp until full development is attained. The larva reaches a length of 860 μm and occupies on average 80% of the polyp volume. The study of the extrinsic and intrinsic aspects which could cause variations in the features of the colonies shows that: the colony form; branching pattern and porosity of the colony; arrangement, distribution and number of polyps; and the resemblance of the sclerites varied as a function of current intensity and direction, water temperature, availability of food and essential compounds, and the presence of commensals. Intrinsic aspects such as growth and reproduction affect the shape of the polyp, the arrangement of the sclerites, the density of the branches and as a consequence, the whole appearance of the colony. It is suggested that these variations might have contributed to erroneous interpretations in the past about the taxonomic classification of the species of the genus ... |
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