They are still generally hermaphroditic and copulate to engage in mutual cross-fertilization, but most of these forms simply produce a few eggs which are either brooded or laid in protective egg capsules and develop directly into tiny turbellarians which look for all the world like the adults. There are however a number of exceptions, which produce a swimming larva. These larvae swim around for a few days prior to settling and metamorphosing into miniature adults, and because they do not feed, are relatively simple to raise in captivity. Most of the large polyclad flat worms of potential interest to reef-keepers will fall into this latter group. A common flatworm in the shallow subtidal of the N. E. Pacific Photo by Ron Shimek Unlike their cousins I mentioned above, the turbellarians are generally not parasitic.
Some species are initially herbivorous, but become carnivorous as they mature.
Others are herbivorous or detritivorous scavengers all their lives, living off microalgae and detritus found on the ocean floor. Most, however, are carnivorous predators or scavengers, feeding on nearly any available animal matter possible to consume. Many species also graze on the bodies of larger, but immotile invertebrates, such as sponges, tunicates, some cnidarians and even some barnacles. In fact, most live rock shipments probably contain numerous small flatworms when introduced into the aquarium, but these animals seldom survive for long in new aquaria, and even if they do, they are so good at hiding that all but the most observant reef keepers will fail to notice them unless they become extremely abundant in the aquarium. A number of the particularly attractive and large polyclad worms are generally benign tank inhabitants worth considering, however.