Meeting Abstract

59.2  Saturday, Jan. 5  How the pilidium larva feeds VON DASSOW, G*; EMLET, RB; MASLAKOVA, SA; University of Oregon; University of Oregon; University of Oregon dassow@uoregon.edu

The nemertean pilidium is a novel larval type that is difficult to relate to other invertebrate larval forms, except inasmuch as the pilidium - like the actinotroch, the mitraria, the endolarva of Polygordius, or the dipleurulas - consists of an inflated, transparent larval body bearing ciliated bands by which it swims and feeds, and within which a juvenile develops from growing rudiments. Like those superficially-similar larval forms, the pilidium feeds on small phytoplankters. The heteronemertean Micrura alaskensis can be raised in the lab from egg to metamorphosis when fed solely with the cryptomonad Rhodomonas. We used high-speed video to describe the feeding mechanism of Micrura's pilidium. Flow generated by the primary ciliated band brings food particles past the band margins. Edible cells, but rarely inert particles, trigger rapid flicks of the pilidial lobes and lappets, re-directing a food particle and surrounding parcel of water into an atrial chamber. Non-beating cilia within the band are the likely sensors that detect edible cells. Once a parcel of food-containing water is engulfed, a secondary ciliated band beats in reverse, as if to barricade the exits while expelling excess water. Slow flow within the esophagus gently moves the cell toward the stomach entrance. Most captured Rhodomonas make repeated attempts to escape by firing ejectisomes, but the size of the chamber and the persistent flow within it seem to defeat the captured cells' efforts, until, their ammunition exhausted, they are drawn defenseless toward the gastric sphincter. This feeding mechanism is striking both for its novelty - it's not like any other larva - and for its familiarity: in inventing its own way to eat, the pilidium converged upon strategies used by Venus' fly trap, a FACS, and the baleen whales.