Larval diversity in nemerteans

The two kinds of nemertean larvae are the transparent helmet-shaped pilidium larva and the opaque bullet-shaped or worm-like planuliform larva pictured on the right. Different planuliform larvae are found in the orders Hoplonemertea and Palaeonemertea (Maslakova et al. 2004, Maslakova and von Döhren 2009). The pilidium larva, characterizes a monophyletic clade called the Pilidiophora, which comprises the order Heteronemertea and the palaeonemertean genus Hubrechtella (Thollesson and Norenburg 2003). The Pilidiophora includes approximately one third of the  1250 described nemertean species (Schwartz and Norenburg 2001, Kajihara et al. 2008).

Pilidium larvae are often found in plankton, but usually in small numbers. Pilidia which belong to different species have recognizably different morphology (Dawydoff 1940, Cantell 1966, 1969, Norenburg and Stricker 2002, Lacalli 2005, also see below). These different types of pilidium larvae presumably belong to different pilidiophoran species,  but in very few cases do we know which species they belong to. One way to know for sure is to rear larvae from eggs of known adults (see on the right). Another way to know is to obtain DNA sequence data from individual  larvae and try to match those to sequences derived from  identified adult nemerteans known to occur in the area (see below).

Molecular identification of nemertean larvae

The nemertean larvae in the slideshow below were collected in the plankton off the coast of Oregon, and identified by sequencing the “barcoding” region of Cytochrome Oxidase I gene and a fragment of 16S rDNA gene. This started as a class project by graduate students Laurel Hiebert and Greg Gavelis in the 2008 Molecular Marine Biology course, taught by Svetlana Maslakova at the Oregon Institute of Marine Biology. We continued collecting nemertean larvae and tissue from the candidate adult species throughout the next year. Students in the MMB 2009 class focussed on the identification of the pilidium larvae using sequence data derived from those larvae and the candidate adult species.

Using sequence data we determined that Pilidium nigrophtalma is the larva of Lineus flavescens. Thanks to the adult nemertean sequences kindly provided by Dr. Jon Norenburg (Smithsonian Institution) we determined that the common hoplonemertean larva in Coos Bay plankton belongs to Carcinonemertes errans (the adult lives and feeds on the eggs of the commercially significant Dungeness crab, Cancer magister). We identified several other larval morphotypes to the genus level, including a palaeonemertean larva, which likely belongs to a new  North American species of Carinoma.

We hope to continue this study throughout the years with the goal of identifying to species level and providing an illustrated guide to the nemertean larvae of the Pacific coast of North America.

All images on this webpage are by Svetlana Maslakova. You may not copy or use them without the explicit permission from the author. The research findings presented here are still unpublished. Please, do not refer to or cite these results in scientific papers or textbooks.