An Analysis of Placozoan Nutrition and Biomineralization

Abstract

Trichoplex adhaerens, the only species in the phylum Placozoa, is the simplest and most primitive of all metazoans. Placozoans are found in the littoral zone of subtropical and tropical oceans, have a plate-like appearance and generally adhere to surfaces. These extremely simple organisms have no organs, muscular system or nervous system. Little information is known about their diet or behavior in the natural environment. In the laboratory placozoans feed via phagocytosis on algae, living protozoa, and detritus, and have been cultured using generic filter feeder food. Experiments were performed in order to compare the success of populations of placozoan strains who were fed a filter feeder medium versus a brine shrimp medium. Placing a single placozoan in a petri dish and allowing it to reproduce asexually in order to clone the organism resulted in different strains. There appeared to be no preference for either media shown between the strains. A significant distinction that was observed between strains was the presence of birefringent granules that exist in a ring around the perimeter of the animal. Optical analysis, combustion experiments, triammonium hydroxide tests, Scanning Electron Microscopy (SEM) and Raman spectroscopy analyses were performed in order to discover the structure and composition of the birefringent granules. Only certain strains were found to contain birefringent granules that remained present over multiple generations, which could imply there might be more than one species of Placozoa. The crystals were found to be inorganic by combustion. Birefringence interference tests indicate that it is improbable that the crystals are of calcium carbonate nature. SEM analysis uncovered crystals that likely originated from the organism that indicate the presence of calcium and oxygen.