Other species focus on sessile benthic invertebrates; sponges, tunicates, bryozoans, and hydroids are staples. Whereas in the winter, they are more carnivorous, eating small mussels, barnacles, bryozoans, and hydroids. The species inhabits the sublittoral zone and occurs amongst hydroids and sea anemones. This nudibranch feeds on hydroids and other marine organisms such as ascidians and sea anemones. Feeds on hydroids and other encrusting fauna. There they feed on algae, barnacles, hydroids and polychaete worms. This sea slug feeds on hydroids which contain "Symbiodinium", microscopic dinoflagellates that are photosynthetic. It feeds on diatoms, detritus film of sand, filamentous algae, hydroids, and pieces of fish. These northern areas are populated with sponges and carnivorous species such as hydroids. Polyps further multiply by growing additional stolons, branches and then polyps, to form colonial hydroids. The thecate hydroids were formerly placed in the paraphyletic "Hydroida" as the suborder Leptomedusa. Most species are predators of hydroids. Bougainvillia is a genus of hydroids in the family Bougainvilliidae in the class Hydrazoa. The hydroids attached themselves to various surfaces and formed small clusters. It consists of cells with a relatively wide diameter called "hydroids", which conduct water.