ABSTRACT
Transmission electron microscopy (TEM) allows very small objects, such as cells and their contents, to be visualised in high detail. Light microscopy and Scanning Electron Microscopy (SEM) has been widely used in taxonomic studies and in the phylogenetic reconstructions that arise from them. TEM, however, has not been used much for this purpose. TEM is essentially no different from other microscopical techniques in that it provides morphological information from which characters of use in phylogenetic reconstructions can be derived. The trick is in identifying useful characters against the confusing background of unimportant detail and artefact. This paper discusses the possibilities and limitations of using TEM-derived characteristics in phylogeny with examples taken from research on echinoderms — mostly on epidermal structures such as tube feet. Several areas of variation in echinoderm ultrastructure are identified as having potential significance in phylogenetic reconstructions. The potential use of sub-cuticular bacteria (SCB) for phylogenetic analysis is discussed.
