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Studies of Recent bryozoan faunas have shown that there is a correlation between colonial growth forms and various physical factors of the environment, especially bathymetry. Each given assemblage of zoarial forms can thus be related to a certain depth interval. In marine Neogene deposits numerous extant bryozoan species occur and some of them have more or less restricted depth ranges: they are used here to complement the indications given by the analysis of growth forms. In the Messinian (uppermost Miocene) of northwestern Algeria a general feature is the occurrence of well-developed diatomaceous deposits interbedded with marl beds where benthic invertebrate remains are often abundant. In the five sections under study bryozoans are represented by 87 species belonging to nine different colonial growth forms. Four different assemblages of these zoarial forms, characterised by presence/absence and …