Nicole Dubilier

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

SummaryTubificoides 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.

Tubificoides benedii (Tubificidae, Oligochaeta) — a pioneer in hypoxic and sulfidic environments. An overview of adaptive pathways

Eutrophic tidal flats and polluted coastal sites are the predominant habitat of the marine oligochaete Tubificoides benedii. The worms live in dense populations in these stressed habitats which are often characterized by high levels of hydrogen sulfide. This indicates that they have a high capacity to tolerate anoxic (and sulfidic) conditions. Respiration rates of T. benedii measured at various oxygen concentrations showed that aerobic respiration is maintained even at very low oxygen concentrations. This ability is combined with a high regulatory capacity of oxygen uptake. Addition of sulfide considerably reduced this capacity of maintaining aerobic metabolic pathways at low oxygen concentrations. The present work in relation to earlier physiological and structural studies (Giere et al, 1988; Dubilier et al., 1994, 1995, 1997) suggests adaptive strategies that make T. benedii one of the most successful inhabitants of ecologically stressed, sulfidic benthic environments. This is corroborated by comparison with other typical’ sulfide annelids’ such as the polychaetes Capitella capitata and Arenicola marina.

Some aspects of the ecophysiology of Tubificoides benedii and ultrastructural observations on endocuticular bacteria

Tubificoides benedii is regularly found in sulphide-rich sediments with extremely low oxygen tensions and can tolerate anaerobic conditions for several days. Although the anaerobic energy production of marine invertebrates has been well studied, almost nothing is known about the anaerobic metabolism of marine oligochaetes. Preliminary results after measuring end-products during anaerobic incubation show that in contrast to all previously examined marine facultative anaerobe invertebrates T. benedii degrades malate during anaerobiosis. Also, the concentration of free amino acids is extremely low for a marine organism. Low levels of free amino acids could be concomitant with malate utilization: the utilization of the amino acid aspartate (as observed in all other examined marine invertebrates) seems to be excluded by the low concentrations of aspartate and other amino acids in T. benedii.