Mystery worm

Perhaps you’ve seen this video recently circulating the web:

 

Nemertean worm, a Gorgonorhynchus sp.

 

Perhaps you also wondered what the heck you were looking at. The quick explanation  that you may have read is that it is a ribbon worm (or nemertean) and what you see shooting out of it is it’s proboscis, an organ that it uses to find and consume food.

But there’s more to the story.  That web of white that shoots out of the worm is not just a simultaneously “gross” or “creepy” and “COOL” anomaly, but an incredibly effective hunting weapon.

At first glance these soft, elongate, teethless worms look far from a formidable foe.  If ever you have the opportunity to encounter one of these worms, you’ll likely discover that they easily fragment into pieces.  They look like the kind of animal that gets eaten, not the one that does the eating.  The reality, however, is that nemerteans (or ribbon worms) are voracious predators.  Nemerteans are able to prey on organisms that are seemingly faster and better defended.  Many of these worms hunt animals that are the same size or larger than themselves.

 
A nemertean eating a fish. Photo credit: David Barnes

A nemertean eating a fish. Photo credit: David Barnes

 

How do they wrangle their prey into submission?  It all comes back to that incredible weapon that is their proboscis.  The proboscis is a long, muscular, fluid-filled tube that can be rapidly extended outside the body. Some nemerteans have a proboscis weaponized with a stylet (think of something like a small sharp knife) that it uses to repeatedly puncture its victim. 

However, many nemerteans lack a stylet and still are able to consume large prey.  How?  With or without the stylet, the proboscis secretes toxins that can immobilize their prey.  Those with a stylet, create opening into which the toxins can enter their victim's body.  Nemerteans lacking a stylet use a different strategy; they extend their proboscis and wrap it around their prey like a lasso, using sticky and toxic secretions to hold onto and slowly subdue their prey.  Once subdued, the nemertean can then swallow its prey whole or suck out the tissues from its prey’s body (see video below of nemertean sucking the tissues out of the exoskeleton of an amphipod).

One nemertean, Cerebratulus lacteus, preys on clams by entering their burrows and either swallowing them whole, or by penetrating the shell through the siphon of the clam and then slurping up the tissues within (Worms have been observed with their “head” inside the siphon of a clam and when the clam shell was opened nothing but a worm head was inside!).

Perhaps more impressive is the ability of Cerebratulus lacteus to also prey upon another type of worm, segmented ragworms (of the family nereididae - annelid worms – marine relatives of earthworms).  You might be thinking, “not impressed, it’s just another soft-bodied worm”.  But ragworms are no slouches.  Ragworms are fast burrowing, swimming worms armed with jaws. Still, they are no match for nemerteans.

The jaws of a nereididae worm that is preyed upon by nemerteans. Photo credit: Malcolm Storey

The jaws of a nereididae worm that is preyed upon by nemerteans. Photo credit: Malcolm Storey

The nemertean, Cerebratulus lacteus, swallowing whole a nereididae worm (similar to that whose jaws are pictured left). Photo credit: James Zhan

The nemertean, Cerebratulus lacteus, swallowing whole a nereididae worm (similar to that whose jaws are pictured left). Photo credit: James Zhan

The process of consuming its prey, happens surprisingly fast, facilitated by the often elongate and highly flexible bodies of nemerteans (some species can stretch up to 10 times their resting length or 3 times their width!).  Check out the video below of several nemerteans (not Cerebratulus lacteus) consuming a neredidae worm; once they've immobilized the ragworm enough to latch on, it is gone in less than a minute (the action really gets going around minute 4):

Several individuals of the heteronemertean Ramphogordius sanguineus were recorded feeding on the polychaete annelid Allita succinea. (Video recorded and edited by SA Caplins)

At first glance the nemerteans seem like an innocuous animal, worth little attention.  Instead, nemerteans are an example of a seemingly simple and vulnerable organism which has a evolved a highly specialized apparatus that turns the tables.

For more nemerteans: 

Nemerteans in Antarctica

Nemertean facts