Epidermal surfaces of the ophiouroid Ophionereis annulata (Le Conte) were examined by scanning electron microscopy. Microvilli, which are characteristic of many transport epithelia, are present on the epidermal surfaces. Epidermal surfaces of freshly-collected brittlestars were compared with brittlestars that were maintained in the laboratory for 48 hours in fresh seawater and in seawater enriched with 20uM glycine. Very few bacteria were observed on the surface of the freshly-collected animals or on animals maintained in the laboratory in fresh seawater. The epidermal surfaces of animals maintained in seawater enriched with 20 uM glycine showed extensive mats of coccoid and bacilloid bacteria. Because of the practical problem of propagation of marine bacteria in the aquarium system, it is unlikely that direct addition of amino acids to supplement nutrition of cultured marine invertebrates would be a viable practice among mariculturists.