Planuliform Nemertean Larvae

In the first of week of January I found egg strings of the nemertean worm Carcinonemertes errans in among the egg mass of a Dungeness crab (Cancer magister). These worms feed on the crabs eggs, acting like parasitic castrators to their hosts. The embryos within the worm egg strings began to hatch out after I agitated them a bit with my forceps.

The larvae that emerged were planuliform uniformly ciliated "blobs" as Svetlana calls them, only about 100 microns long. They contained lipid droplets and two eye spots. Each larva had cirri at both their posterior and anterior ends. These cirri, together with the cilia covering the body, were used for locomotion, helping the larvae swim in a distinctly zig-zag pattern.

I kept the larvae in large glass containers, changing the water every two days. By the time the larvae were three weeks old they had begun elongating and looking a lot more like young worms. The rudiments of many juvenile structures are present within the larvae, including the proboscis.

To date, I have several cultures of C. errans larvae, the oldest of which are nearly 50 days old. They have not begun to settle out yet, nor have they developed much further, which leads me to think that they might have a rather long planktonic life span or need more specific food and/or settlement cues that I have not yet exposed them to. I'll just have to keep trying new things. Isn't science great?