Young, C. M.*; Vazquez, E.: How carnivorous deep-sea ascidians catch their prey.

Two new species of carnivorous deep-sea octacnemid ascidians have recently been discovered at bathyal depths in the Bahamas, one in the genus Dicopia and one in the genus Kaikoja. Analysis of gut contents indicates that both species consume mostly small crustaceans, though we also observed entrapment of a small fish by Kaikoja sp., the larger of the two. Because these animals have reduced branchial sacs and lack ciliated stigmata, they cannot filter particles like other ascidians. It has been widely assumed in the literature that an octacnemid traps prey like a Venus flytrap plant, closing rapidly on small animals that contact the inside surface of its incurrent siphon. However, video observations from a submersible failed to reveal any instances of food capture by rapid closure; instead, movements are generally slow and deliberate. Most individuals live on vertical rock walls with the expansive incurrent siphon pointed downward and the small excurrent siphon directed upward into the water column. In situ studies with fluorescent dye revealed that internal flow is induced by ambient currents in the benthic boundary layer. Passive flow draws prey into the incurrent siphon, where they are unable to escape from reflexed folds of tissue. Once captured, prey are moved to the esophagus by rapid pumping of the body, which is accomplished with strong anterior muscles situated between the siphons. These two octacnemids are more like minnow traps than Venus flytraps.