All known examples of
Aphelidium are
obligate parasites of
freshwater phytoplankton. As parasites, the life cycle of
Aphelidium is closely tied to its ecological relationship with its hosts. The cycle begins with the motile
Aphelidium zoospore contacting its host, a
green alga. The attached zoospore first encysts then inserts an infection tube into the host cell, priming the ingress of the
Aphelidium. As the parasite expands within the host cell, it develops into a
multinucleate plasmodium which grows to eventually replace the entirety of the host cytoplasm. Now all that remains of the green alga is its cell wall and the residual body, a clump consisting of host cell fragments indigestible to the parasite. The
Aphelidium plasmodium then proceeds to divide into
uninucleate cells which develop into
zoospores, using the cell wall of the host alga as a
sporangium. Finally, the uniflagellate zoospores erupt the husk of the host cell via the same puncture made by the infection tube of the parent
Aphelidium to seek new green alga hosts. == Practical importance ==