| dc.description.abstract | In this thesis I report the results of the first study of a symbiosis between an abyssal sea anemone and a scaphopod. I describe the sea anemone as Benthactis nomadas n. g., n. sp.The sea anemones and scaphopods were collected at a soft-sediment site at 4100 m depth in the northeastern Pacific Ocean. Sea anemones of this species were always attached to a scaphopod shell; thus, I infer that the symbiosis is obligate for the sea anemone. I conclude that the symbiosis is facultative for the scaphopod because 8% of the shells showed no evidence of recent sea anemone attachment. I infer from sea floor photographs and from the fact that these organisms are trawled that the scaphopods carrying these sea anemones live at or near the surface, an atypical habitat for a scaphopod. I hypothesize that this symbiosis is initiated when a planula larva of Benthactis nomadas, n. g., n. sp. lands on the exposed dorsal tip of a scaphopod shell. The results of a biomechanics experiment I conducted support my hypothesis that as the sea anemone grows, the scaphopod adjusts its position in the sediment because remaining near the surface requires less energy than dragging a sea anemone through the sediment. Typically, a scaphopod at the sediment surface would be exposed to pelagic and epibenthic predators; I infer that this scaphopod is protected from its predators by the sea anemone. Under the protective shelter of the anemone, the scaphopod can remain at the sediment surface and forage in upper layers of sediment that contain more energy than deeper layers.The sea anemone also benefits from the symbiosis. It receives an attachment site in an environment where hard substratum is limited, and it may gain increased access to food.Based on the results of experiments that I conducted and on inferences, I propose that the relationship between the sea anemone and the scaphopod is mutualistic. | en_US |
