Seven new 3-alkylpyddines, showing alarm pheromone activity, have been isolated from three Haminoea cephalaspidean molluscs: H. orteai, H. orbignyana and H. fusari. Structures were elucidated by spectral analysis; absolute stereochemistry was determined by applying Masher's method. Cephalaspidean molluscs are characterized by a prominent head and by inadequate protection of a shell that is either small and fragile or internal. The first chemical studies on cephalaspideans revealed the presence in the Pacific Aglajide Navanax inermis of a series of metabolites, e.g. navenone-A (l), which when secreted into the mucus act as alarm pheromones inducing an immediate escape reaction in following conspecifics. Recently, metabolites related to navenones were found in some Mediterranean cephalaspidean molluscs: lignarenone-A (2) and -B (3) from the Cylichnidae Scaphander lignarius and haminol-A (4) and haminol-B (5) from the Haminoeidae Haminoea navicula. Because of the interesting biological properties of haminols, which like navenones act as alarm pheromones, we have begun a chemical investigation of other Mediterranean Haminoea species.