the surrounding environment. The mismatch between internal and external symbiont communities suggests that acantharians can be selective in choosing symbionts and probably do not continuously digest and recruit new symbionts, and maintain symbionts for extended periods of time instead. Life cycle Adults are usually multinucleated. Earlier diverging clades are able to shed their spines and form cysts, which are often referred to as reproductive cysts. Reproduction is thought to take place by formation of swarmer cells (formerly referred to as "spores"), which may be flagellate, and cysts have been observed to release these swarmers. Non-encysted cells have also been seen releasing swarmers in laboratory conditions. Not all life cycle stages have been observed, however, and no one has witnessed the fusion of swarmers to produce a new acantharian. Cysts are often found in sediment traps and it is therefore believed that the cysts help acantharians sink into deep water. Genetic data and some imaging suggests that non-cyst-forming acantharians may also sink to deep water to release swarmers. Releasing swarmer cells in deeper water may improve the survival chances of juveniles. Study of these organisms has been hampered mainly by an inability to "close the lifecycle" and maintain these organisms in culture through successive generations. References