Algal photosensory apparatus probably represent multiple parallel evolutions

We postulate that algal photoresponse mechanisms are of relatively recent origin and represent numerous parallel evolutions. Functional differences among them are evident, and it is unlikely that any one can be taken as a "model system" representing all. It is probable that the light antenna is the only truly novel part of the apparatus in most cases, with the signal-processing and motile elements being borrowed from some other, more ancient, sensory system. It is thus anticipated that the light-antennae will show the greatest phylogenetic variation, whereas the signal-processors and motile elements will resemble those of other sensory systems in the same groups of organisms.