The morning of the 4th of May, our Embryology class met an hour earlier than usual and descended into the mudflats behind the “Fisherman’s Grotto” restaurant in Charleston, OR. We are studying the development of spiralians, a large supra-phyletic group of protostome animals that undergo spiral cleavage. Today our goal was to collect worms of two spiralian phyla (nemerteans and annelids), and a representative of a third (non-spiralian) phylum - the Phoronida, to culture in class.
First, we collected the polychaete annelid, Owenia collaris. Owenia lives in a soft, flexible sandy tube and has a very interesting larva, called the mitraria, unique among the polychaetes. We also collected two species of nemerteans which have the pilidium larva: Cerebratulus cf. marginatus (the large brown worm in the palm of a student in the third picture), and Micrura alaskensis. Cerebratulus is very fragile, and easily breaks into many pieces, so we had to be very careful when extracting the worm from the mud. M. alaskensis is a small, pink nemertean that looks like a tiny thread in the mud. Though small, M. alaskensis is common, ranges from Alaska to northern California, and is easily raised to metamorphosis on a diet of unicellular algae.
Last but not least, we collected the phoronid worms, Phoronopsis harmeri (formerly known as Phoronopsis viridis). P. harmeri lives in a thick rigid sandy tube 15-20 cm long. Phoronids are commonly known as “horseshoe worms” because of the characteristic crown of feeding tentacles, called the lophophore, arranged in a horseshoe pattern around the mouth of the adult worm. P. harmeri, like most phoronids, has a unique planktotrophic larva, the actinotroch, which is characterized by a pre-oral hood, and a crown of tentacles used for feeding.