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Gammarus aequicauda (Martynov, 1931) and Gammarus insensibilis Stock, 1966 have been the subject of a quantitative ecological research project in the lagoon system of Bages-Sigean (France, dépt. Aude). From April 1976 till August 1977 samples have been taken at 31 different stations all over the lagoon at intervals of about 2 weeks. With the samples thus obtained we studied the biology and distribution of the two species in relation to environmental factors, the most important being chlorinity and temperature.

The priapulid Halicryptus spinulosus has an outstanding resistance to anoxia and hydrogen sulfide, which enables the animal to survive in deteriorating environments . Whole-body staining procedures, as well as light and scanning electron microscopy were used to study structures and mechanisms possibly involved in sulfide detoxification .The cuticle of the trunk is covered by a coat of mucus and bacteria . Within this coat considerable amounts of finely dispersed iron are precipitated, probably as a Fee +-compound . It is suggested that the iron functions as a rechargeable buffer against hydrogen sulfide, protecting both the bacteria and the priapulid host . Although this chemical shield may not alone account for long-term protection, it allows the animal to gain time for metabolic adaptations .

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