FOOT-RAISING BEHAVIOR AND ACTIVE PARTICIPATION DURING THE INITIAL PHASE OF POST-METAMORPHIC DRIFTING IN THE GASTROPOD LACUNA SPP

Macrocinematographic video recordings showed that Lacuna spp. can produce a mucous thread and initiate drifting when exposed to water flows (particularly oscillating currents). The gastropods can play an active role in their dispersal by raising the metapodium - regardless of their orientation to water flow direction - until most of the sole's surface no longer contacts the substratum (only the most anterior [propodial] region remains fixed). The mucus produced and accumulated at the posterior of the sole of the foot is then taken away with the water current, and stretched up to 160 times the length of the gastropod. The mucous thread pulled by water currents then transports the gastropod, enabling it to drift in an almost neutrally buoyant fashion. In Lacuna spp., the production of a mucous thread also greatly reduces sinking rates (3- to 8-fold), while extension of the foot and antennae during the descent does not. Mucous threads also increase the drifting gastropod's ability to obtain rapid contact with, and attach to, nearby substrata.