Cells containing aragonite crystals mediate responses to gravity in Trichoplax adhaerens (Placozoa), an animal lacking neurons and synapses.

摘要: Trichoplax adhaerens has only six cell types. The function as well the structure of crystal cells, least numerous type, presented an enigma. Crystal cells are arrayed around perimeter animal and each contains a birefringent crystal. resemble lithocytes in other animals so we looked for evidence they gravity sensors. Confocal microscopy showed that their cup-shaped nuclei oriented toward edge animal, shifts downward under influence gravity. Some spontaneously lack these behaved differently upon being tilted vertically than with typical number cells. EM revealed contacts fiber epithelial but lacked features synapses. spectroscopic analyses crystals consist aragonite form calcium carbonate. We thus provide behavioral able to sense gravity, likely be receptors. Moreover, because placozoans thought have evolved during Ediacaran or Cryogenian eras associated seas, made aragonite, may acquired sensors this early era.