Over a period of several years, organisms inhabiting or breeding in the intertidal sand and salt marshes of Cape Cod were collected when these areas were sampled for bloodsucking Diptera. A taxonomic list of identified organisms, including insect larvae and adults, is given with limited ecological data on the collecting sites. Taxa with identified species from the intertidal sand areas include: Platyhelminthes (one family and one species): Mollusca (8 families, 8 genera, and 7 species); Annelida (7 families, 10 genera, and 10 species); Arthropoda (23 families, 23 genera, and 25 species). Taxa with identified species from the salt marsh areas include: Mollusca (4 families, 4 genera, and 3 species), Annelida (10 families, 15 genera, and 14 species), and Arthropoda (47 families, 74 genera, and 76 species).