Meeting Abstract

P2.155  Saturday, Jan. 5  How the pilidium larva pees VON DASSOW, G*; MASLAKOVA, SA; University of Oregon; University of Oregon dassow@uoregon.edu

In the course of our ongoing studies of how the pilidium larva feeds and and how the pilidium larva grows, we quite unexpectedly learned how the pilidium larva pees. Relatively early in the larval life of the heteronemertean Micrura alaskensis, a pair of protonephridia appear, associated with the forming trunk imaginal disks. Initially containing a single terminal unit each, the nephridia are located just behind the ciliated ridges at the back of the esophageal chamber. On each side a short nephridioduct penetrates the trunk disk and opens into the amniotic cavity, which is connected to the outside world at the underside of the posterior lobe via the amniotic pore. This happens to be approximately where an excurrent leaves the esophageal chamber. This means that these protonephridia filter the blastocoelic fluid into the amniotic space, which in turn remains open to the outside, and that the products of excretion are likely carried away from the mouth by the excurrent. As the juvenile develops, additional units appear on branches of the same duct, and are incorporated into the young worm alongside the developing juvenile foregut. Pilidial nephridia, which may have been identified by Otto Bürger in 1894 but apparently went unnoticed by others until now, are significant developmentally because they represent an early-forming, larval organ which is retained by the adult after metamorphosis; the only other organ so retained is the stomach.