Sensory mechanisms: phototaxes and light perception in algae
ABSTRACT Most photosynthetic flagellates have evolved various photo-orientation mechanisms after the acquisition of chloroplasts. For phototactic responses, eyespot apparatuses (EAs) are usually involved in light perception. As the endosymbiosis of chloroplasts occurred multiple times, the EAs are polyphyletic. We classified known EAs of algae into the following types considering the phylogenetic origins and the fine structural features: first, Chlorophyte type; second, Cryptophyte type; third, Euglenophyte type; fourth, Phaeophyte type; fifth, Eustigmatophyte type; sixth, Dinoflagellate type (five subtypes). In addition we discuss and summarize aspects of signalling elements and flagellar responses involved in photoresponses in the green algae.