Studies on the free-living protozoan fauna of estuaries in the coastal zone of Tamil Nadu, India Author Bindu, L. text Records of the Zoological Survey of India 2021 121 1 61 75 journal article 10.26515/rzsi/v121/i1/2021/141506 2581-8686 13186453 9. Arcella megastoma Penard, 1902 Material examined : Mi-129, 3 ex. , Karaikkal estuary, 02.vii.2012 ; Mi-198, 5 ex. , Kaduviyar estuary, 06.xii.2013 ; Mi-214, 3 ex. , Coleron estuary, 06.xii.2013 ; Mi-219; 6 ex. , Arasalar estuary, 06.xii.2013 ; Mi-253; 4 ex. , Kaliveli estuary, 21.vii.2014 ; Mi-264; 3 ex. , Vettar estuary, 20.vii.2014 . Diagnosis : Shell very flattened with a wide aperture; ratio diameter aperture/shell usually 0.45-0.53; with 2 to 200 nuclei; measurements 160-301 µm, diameter of aperture 87-190 µm. Distribution in India : Andhra Pradesh , Himachal Pradesh , Tamil Nadu (present record).