AN ENDOCRINE BRAIN - THE PATTERN OF FMRFAMIDE IMMUNOREACTIVITY IN ACOELA (PLATHELMINTHES)

In order to solve the problem of whether the Acoela have a brain of a common flatworm type, an immunocytochemical study was performed of the pattern of FMRF-amide in the nervous system of four species of Acoela , Anaperus biaculeatus, Childia groenlandica, Actinoposthia beklemisch evi and Mecynostomum sp, In all species a FMRF-amide positive bilobed brain-like structure lacking neuropile was observed. This brain is com posed of large multipolar nerve cells with short processes, The FMRF-a mide immunoreactivity appears as spots in the cytoplasm. Short lateral branches originating from the periphery of the brain were observed in Anaperus biaculeatus, No immunoreactive nerve cords were detected, Th e results indicate that the brain-like structure of Acoela is not homo logous with the brains of other Plathelminthes and implies an independ ent evolution of Acoela.