DEVELOPMENT OF THE SYMBIOSIS OF CONVOLUTA ROSCOFFENSIS GRAFF AND PLATYMONAS SP.(1)

The acoel flatworm Convoluta roscoffensis is infected by the alga Platymonas sp. The ova and young Convoluta do not contain algae, and each generation must be reinfected. The infecting algae undergo morphological alterations when within the worm. Flagella, theca, and eyespot are lost in that order. Flagellar basal bodies and striated rootlets remain. Loss of theca may be the result of a dissolution process, possibly the result of enzymes from the animal or from the algae. Upon loss of theca, the alga assumes an irregularly shaped form. Fingerlike processes of the algal cells penetrate between adjacent animal cells. This form is present in all but the earliest stages of infection, and may be a prerequisite for the establishment of a balanced photosynthetic mutualism.