To Be or Not to Be a Flatworm: The Acoel Controversy
Localization of BrdU-containing cells in the acoels Isodiametra pulchra, Neochildia fusca and Aphanostoma sp. after a short BrdU pulse (A–B, E–F, H) and 10 days chase (C–D, G). (A, C, E, G–H) wholemounts of adult animals, (B, D, F) semithin cross sections. Insets: details of the epidermis, encompassed by dotted lines. Anterior to the left. (A–B, E–F, H) Note the lack of S-phase cells (brown nuclei) in the epidermis after 30 min BrdU pulse. (C–D, G) BrdU-labeled cells (brown nuclei) migrated from the mesodermal space to the epidermis and differentiated into epidermal cells during the 10 days chase period. Asterisk denotes diatom in digestive parenchyma. Scale bar is 50 µm for (B, D, F, H), 100 µm for (A, C), and 200 µm for (E, G).