Microscopic worm like animals, adult Orthonectida have a single layer of cells featuring clila surrounding a mass of cells which can perform reproduction.
When they reproduce, the adults are released from the host, and sperm from the males penetrate the females to fertilize them. The zygote develops into a ciliated larva that escapes from the mother to seek out new hosts. Once it finds a host, the larva loses its cilia and develops into a syncitial plasmodium larva. This, in turn, breaks up into numerous individual cells that become the next generation of adults