Tales from Poseidon

This past summer, Maddy worked on a project at the marine lab to document as many local species of ribbon worms (nemerteans) as she could find in the Bodega Bay area.  Gabriel, Alisha, and Sarah helped with the search and scooped up a few bags of sediments from the shallow subtidal zone off Doran Beach.  Within those sediments was a very interesting nemertean that we had not seen before. 

Below is a photo of the whole ribbon worm.  When contracted, the worm had a stout and short body, only about 12 mm long: 

 

 

At the pointy tip of its head, it has two conspicuous eyespots (called ocelli). They're tiny, so look closely.  [They're easier to see in the video clip below.]

 

Compared to most other ribbon worms, one of the most unusual aspects of this worm is its habit of drawing the tip of its head back into its body, which forms a “collar” of tissue that surrounds the retracted head:

 

Like other ribbon worms that belong to this taxonomic order (called hoplonemerteans) the proboscis that snares its prey was armed with a sharp stylet that helps in prey capture.  In the photo below you can see the central stylet that fits into a holder (called a basis), which looks a bit like the handle of a screwdriver:

 

Remarkably, if a nemertean’s stylet is lost or damaged, it is replaced with a new one that is moved into the holder!  In the photo above, you can see two accessory pouches (one on the left and one on the right), each holding 3 new stylets.

When we looked through the taxonomic guides, all of these characteristics seemed to be a good match for Poseidonemertes collaris.  This species was first described from specimens collected in intertidal sandy mud in Bodega Harbor in the early 1980s (Roe and Wickham 1984).

Some nemertean species are difficult to identify from their appearances, so as part of Maddy’s project, she sent small tissue samples off to Oregon for DNA sampling.   When the DNA sequences and analyses came back this week, our colleague Svetlana had a surprise for us.  Although this ribbon worm is closely related to Poseidonemertes collaris, the DNA sequences are distinct enough that this is likely a new, previously undescribed species of Poseidonemertes!

Eric was able to capture some video of this fascinating ribbon worm.  In the video, you will see the worm crawling.  Then (at about 35 seconds) watch for close-ups showing the characteristic behavior of the animal quickly retracting the tip of its head.  [If you're reading this in an e-mail and you can't see the video below, click on the title of this post to go to the web page to watch it.]

You might be wondering how this unusual ribbon worm got the name Poseidonemertes? Although we assume the name is associated with Poseidon, we have been unable to find more details regarding how this group of nemerteans came to be associated with the Greek god of the sea and earthquakes.

Many thanks to Maddy, Gabriel, Alisha, Sarah, Eric, and Svetlana for finding and documenting this fascinating worm.

Reference:  Roe, P. and D.E. Wickham. 1984.  Poseidonemertes collaris, n. sp. (Nemertea: Amphiporidae) from California, with notes on its biology.  Proceedings of the Biological Society of Washington 97: 60-70.