EXTREMELY food-poor environments, such as the deep sea, place extraordinary demands on organisms with respect to feeding, resulting in modifications of the feeding strategies found in shallow waters. A general rule is that macrophagy becomes a better strategy than microphagous suspension-feeding1-3. The characteristics by which phyla are defined, nonetheless, remain unchanged in these adaptations. We present here an apparently unique example of a fundamentally different body plan, derived from a pre-existing phylum, occurring in deep-sea sponges. We demonstrate that the Cladorhizidae have evolved carnivory and capture small crustaceans by means of filaments provided with raised hook-shaped spicules. This adaptation to a food-poor deep-sea environment has resulted in the loss of the diagnostic characteristics of the phylum Porifera: an aquiferous system and choanocytes.