ABSTRACT
In order to investigate the possible use of dissolved organic matter (DOM) by the tissues of Amphipholis squamata, ultrastructural, auto-radiographic and scintillation counting methods of analysis were applied to adult and embryonic tissues. Before metamorphosis, external epithelial cells of vestigial plutei do not form flagella or flagellated bands typical of the free-living ophio-pluteus stage of most brittle-stars. Instead, such cells prematurely secrete a cuticle and become associated with bacteria. Grain counting of plastic sections indicates that bacteria absorb radiolabelled amino acids and glucose from such currents more readily than do cells of the adult or embryonic epithelia. Chloramphenicol (4mM) greatly reduces total incorporation of radiolabelled amino acids, suggesting that bacteria can quickly and effectively utilize our artificial DOM and that protein synthesis occurs principally in prokaryotic cytoplasm. Vestigial plutei do not phenotypically express aspects of their developmental program leading to a swimming (e.g., spicule-supported larval arms) planktotrophic larva (mouth is absent prior to metamorphosis).
