SANTAGATA, S.; Smithsonian Marine Station: Functional design of ciliary swimming in non-feeding bryozoan larvae

Non-feeding larval forms produced by bryozoans are ideal for testing hypotheses regarding the functional designs for swimming in the plankton due to their diverse cytological architecture yet overall simplified shape. Previous work has shown that the structure of the presumptive juvenile tissues are generally conserved among systematic groupings, however the cytological arrangement and morphology of the multiciliated coronal (larval) cells has been modified several times. The ctenostome bryozoans exhibit the greatest degree of cytological diversity possessing forms that appear functionally convergent with and divergent from other bryozoan systematic groups. It has been demonstrated previously that the coronal cilia of cyphonautes larvae increase in length during development (maximum length of 60 microns), however most non-feeding bryozoan larvae are more extensively ciliated and each cilium is usually a third of this length. My investigations of tethered larvae with high-speed video microscopy have found that cilia of non-feeding forms have higher velocities at their tips than do locomotory cilia of similar length of other larval forms. These new observations also show that turning behaviors are at least partially the result of localized ciliary arrests. Confocal microscopy used in conjunction with fluorescent probes for F-actin and tubulin has resolved patterns in the larval neuromuscular system in relation to locomotory structures. Sensory cells positioned between and adjacent to coronal cells (intercoronal cells and ocelli) are at least bipolar neurons that directly connect with the equatorial nerve ring. These data along with previous descriptions of gap junctions among sensory cells and their effectors as well as the behavioral switches induced by neurotransmitters allow for the development of a model of larval swimming.