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First data on the spatial and temporal distribution of the mysid community in the “Stagnone di Marsala” (western Sicily) from January to December 1996 are reported. The assemblage consists mainly of five species which are common in the Mediterranean Sea: Diamysis bahirensis (55.2%), Siriella armata (18.6%), S. clausii (15.8%), Mysidopsis gibbosa (9.8%) and Mesopodospis slabberi (0.6%). Population structure is described for each species and the reproductive period inferred. A sharp increase in abundance occurred in the spring, while the minima occurred during autumn-winter. The D. bahirensis dominated from March to October and S. clausii in the winter. A large difference, which was mainly quantitative, was recorded between the population from the inner area and that from the area more influenced by the sea. Clear seasonal patterns and spatial segregation in the inner part of the sampling area were observed.

Only three of the twenty species at present ascribed to the genusMysidopsishave been recorded around the coasts of Britain; these areM. gibbosaG. O. Sars,M. didelphysNorman andM. angustaG. O. Sars. The latter species is rare and has never been caught in large numbers. Large catches ofM. gibbosaare made in certain sandy bays in the Firth of Clyde and the species is quite common in Gaineamh Smuagh, a sandy bay in Loch Ewe, Wester Ross (Mauchline, 1965 a). The largest species,M. didelphys, occurs at greater depths than the other two and, likeM. gibbosa, is often common in certain areas, especially in the deep troughs of the Firth of Clyde and in some of the west coast lochs of Scotland, for example the upper part of Loch Etive.