Structural peculiarities of the body wall of Tubificoides benedii (Oligochaeta) and possible relations to its life in sulphidic sediments

Summary Tubificoides benedii [=Peloscolex benedeni] a ubiquitous tubificid from poorly oxygenated, often polluted coastal muds, is known to be exceptionally well adapted to sulphidic sediments. However, almost nothing is known about its structural peculiarities, such as the conspicuously papillate body surface and possible relations to its unusual ecology. As a consequence, a study of this abundant but extraordinary marine worm has been made with the use of light and electron microscopy. While many internal structures correspond to the general pattern of marine tubificids and are not mentioned here, the epidermis — cuticle complex is unusual. The thick cuticle forms numerous high leaf-shaped papillae covered by condensed, almost solid mucus caps. The intermediate furrows usually harbour many different bacteria embedded in mucus. This mucus cover is rich in precipitates containing sulphur and other xenobiotic substances. Together with the cuticular papillae it can be sloughed off in a moulting process. Epicuticular projections, usually typical of oligochaetes, are absent from most parts of the body except from the first and last segments. The epidermal cells often contain numerous extremely long and abnormally shaped mitochondria. The significance of the peculiar structure of the body wall and the distinct moulting are discussed in the light of the ecological situation of these tubificids.