Pilidia in the plankton

On February 11, 2010 Marley Jarvis, a PhD student in Alan Shanks' lab at the OIMB, did a surface plankton tow off the F dock in the Charleston marina (Charleston, OR). She timed the tow to sample at high tide and used a 153 micron plankton net. She caught a lot of interesting animals, including several kinds of nemertean larvae. One of the most common morphotypes of nemertean larvae was a pilidium larva, which we named Pilidium megacephala because it has relatively large cephalic imaginal discs. Likely, this larva belongs to the genus Micrura. We are currently working to get the DNA sequence from it, to try to identify which species it belongs to.

Another kind of nemertean larva Marley found was also a pilidium, but of a different sort. Its morphology suggests that it belongs to the palaeonemertean genus Hubrechtella, or one of its relatives in the family Hubrechtiidae. It is characterized by relatively small lateral lappets displaced toward the posterior, a large anterior lobe, very large and conspicuous squamous epithelial cells with prominent nuclei, and lack of a muscle retractor, which in other pilidium larvae connects the apical organ to the esophagus. Our pilidium resembles the type of larva called Pilidium auriculatum described by Leuckart and Pagenstecker (1858) from the European waters. A similar pilidium from Swedish waters was identified as belonging to Hubrechtella dubia by Cantell (1969). Pilidium auriculatum type of larva had also been found in the Gulf of Mexico (George von Dassow, pers. comm.), in the Gulf Stream off the Atlantic Coast of Florida (Norenburg and Stricker, 2002) and in the Sea of Japan (Chernyshev, 2001). So far no hubrechtid nemerteans are known to occur on the West Coast of North America.

Cantell, C.-E. 1969. Morphology, development, and biology of the pilidium larvae (Nemertini) from the Swedish West Coast. Zool. Bidr. Uppsala. 38:61-112.

Chernyshev, AV. 2001. The larvae of unarmed nemerteans in Peter the Great Bay (Sea of Japan). Russian Journal of Marine Biology. 27(1): 58-61.

Leuckart, R. and A. Pagenstecker. 1858. Untersuchungen über niedere Seethiere. [Studies of lower marine animals]. In German. Arch. Anat. Phys. p. 569-588.

Norenburg and Stricker. 2002. Nemertea. Atlas of Marine Invertebrate Larvae, C. M. Young, M. A. Sewall, and M. E. Rice, eds. Academic Press, San Diego. Pp. 163–177.