U. poseidonis shows two types of movement, swimming and burrowing into the sediment (Watkin, 1939a). Little is known of its life cycle. Generally, breeding behaviour of infaunal amphipods is influenced by location. In deeper waters the spring rise in temperature initiates breeding, while in shallower waters it is induced by tidal phasing (Wolff, 1973; Fish & Fish, 1989). The species of the genus Urothoe may be considered selective deposit feeders. They feed by cleaning sand grains from adhering micro-organisms and detritus (Nicolaisen & Kanneworff, 1969).