This paper describes inter-specific differences in the distribution of sediment in the gut compartments and in the
enzyme and bacterial profiles along the gut of abyssal holothurian species — Oneirophanta mutabilis, Psychropotes
longicauda and Pseudostichopus villosus sampled from a eutrophic site in the NE Atlantic at different times of the
year. Proportions of sediments, relative to total gut contents, in the pharynx, oesophagus, anterior and posterior intestine
differed significantly in all the inter-species comparisons, but not between inter-seasonal comparisons. Significant differences
were also found between the relative proportions of sediments in both the rectum and cloaca of Psychropotes
longicauda and Oneirophanta mutabilis. Nineteen enzymes were identified in either gut-tissue or gut-content samples
of the holothurians studied. Concentrations of the enzymes in gut tissues and their contents were highly correlated.
Greater concentrations of the enzymes were found in the gut tissues suggesting that they are the main source of the
enzymes. The suites of enzymes recorded were broadly similar in each of the species sampled collected regardless of
the time of the year, and they were similar to those described previously for shallow-water holothurians. Significant
inter-specific differences in the gut tissue concentrations of some of the glycosidases suggest dietary differences. For
example, Psychropotes longicauda and Pseudostichopus villosus contain higher levels of chitobiase than Oneirophanta
mutabilis. There were no seasonal changes in bacterial activity profiles along the guts of O. mutabilis and Pseudostichopus
villosus. In both these species bacterial activity and abundance declined between the pharynx/oesophagus and
anterior intestine, but then increased along the gut and became greatest in the rectum/cloaca. Although the data sets
were more limited for Psychropotes longicauda, bacterial activity increased from the anterior to the posterior intestine
but then declined slightly to the rectum/cloaca. These changes in bacterial activity and densities probably reflect changes
in the microbial environment along the guts of abyssal holothurians. Such changes suggest that there is potential for
microbial breakdown of a broader range of substrates than could be otherwise be achieved by the holothurian itself.