A few species that live in waters where the supply of food particles is very poor prey on crustaceans and other small animals. So far only 137 species have been discovered.[30] Most belong to the family Cladorhizidae, but a few members of the Guitarridae and Esperiopsidae are also carnivores.[31] In most cases little is known about how they actually capture prey, although some species are thought to use either sticky threads or hooked spicules.[31][32] Most carnivorous sponges live in deep waters, up to 8,840 m (5.49 mi),[33] and the development of deep-ocean exploration techniques is expected to lead to the discovery of several more.[14][31] However one species has been found in Mediterranean caves at depths of 17–23 m (56–75 ft), alongside the more usual filter feeding sponges. The cave-dwelling predators capture crustaceans under 1 mm (0.039 in) long by entangling them with fine threads, digest them by enveloping them with further threads over the course of a few days, and then return to their normal shape; there is no evidence that they use venom.