Marine Organism of the Day – “The Alien”

Ok, I definitely won’t be able to post information about organisms I see every day, but here’s a start to what hopefully will become a fairly regular thing.

A few weeks ago, I visited a marina in Bodega Bay, California to collect organisms for an upcoming experiment. A local fisherman stopped me to ask what I was up to, and we chatted for a bit about my research and his livelihood. He was very knowledgeable about many of the organisms that I sought on the marina’s docks, and he wanted to point one out that he didn’t know much about. What he knew was that it was one of the few dock organisms that fared well after a recent harmful algal bloom that directly or indirectly harmed many organisms on the Northern California coast, including abalone and purple sea urchins.

What the fisherman did not know was what kind of organism it was; he referred to them as “aliens.” We walked together to a nearby boat slip and peered over the edge. What I saw was a purple, dome-shaped mass about 8 inches in diameter stuck on the dock, just below the water line. It was pock marked like a golf ball or the surface of the moon, and it jiggled in the gently flowing water. I reached down to touch it and found it had almost no structure. It was very much like a big ball of snot. I told the fisherman that I wasn’t sure what it was, but probably some colonial animal that feeds on material suspended in the water column.

I was annoyed that I didn’t have a better sense of what this critter was, so I went back for a closer look. I woke to a gorgeous day in Bodega Bay and headed out to the marina. The water was flat like a pane of glass, even offshore, and the sun was shining brightly. Many of the boat slips were empty, so the fishers must have been taking advantage of the lovely weather. I went back to the spot where I had seen the alien previously and laid face down on the dock to get a closer look.

First shot of "the alien"

First shot of “the alien”

I found the alien mass once again, but this time it was personal. The sun provided good lighting, the boat in that slip was out to sea, and I had my camera. I took a few minutes to just sit and watch. I noticed that there were some kinds of feeding structures protruding from the surface of the dome that seemed to spontaneously retract back into the heart of the colony.

I played around with this behavior a bit, poking and prodding at the colony’s surface. When I gently touched one feeding structure, it quickly darted to safety. When I touched a few structures at once, a handful retracted including some that I did not touch. Finally, I put my whole hand on part on the colony and shook it slightly. Nearly every feeding structure retracted in a rapid wave, reminiscent of some common audience participation played backwards.

I still did not know what this creature was, so I took some close-ups that would hopefully reveal more about its identity. I was fortunate to get a few shots in focus:

Partly zoomed in photo of Myxicola cf. aesthetica

Partly zoomed in photo of Myxicola cf. aesthetica

Macro shot of Myxicola cf. aesthetica

Macro shot of Myxicola cf. aesthetica

What I could tell immediately was that I was dealing with a worm, and specifically a polychaete worm. Based on the photos, I could see rings of fairly stout tentacles projecting from worms’ heads. This reminded me of feather duster worms, and gave me a strong inkling that these worms were members of the family Sabellidae. After talking with experts at Bodega Marine Laboratory (Eric Sanford and Jackie Sones), we determined that this worm might be in the genus Myxicola. Only two species in this genus are described in California, with one, Myxicola aesthetica, “often found in masses attached to ropes or other sunken objects; <50 mm long” (Carlton 2007). I may have found a match!

There are two curious characteristics about this organism that I want to share. First, the genus Myxicola is known for its ‘giant axon’, or nerve, that runs nearly the entire length of the worm’s body. This giant axon directly innervates the worm’s muscles and presumably aids in super-fast retraction of the unprotected feeding structures back into the tubes.

Having these outsized nerves makes these worms model organisms for the study of nerve function. Another type of organism that has a similarly large axon is squid. They use this giant axon in their jet propulsion system, presumably to aid in rapid predator escape (perhaps these similar traits represent convergent evolution toward a common function). One nice thing about using the worm as a model system over the squid is that the worms are sessile as adults and can be found near the coast throughout much of the year.


The two sets of diagrams show the structure of Myxicola’s nerve cord. The top figure shows the location of the nerve cord in the dorsal (belly) side of the worm and its physical structure. The bottom figure shows a transverse section cut through the nerve cord (like a cut across the belly to eviscerate prey or foe) . Note the feathery structures on either side of the nerve cord represent longitudinal muscles. Adapted from Gilbert 1975 and Nicol 1948.

The other interesting thing about Myxicola is that it can reproduce both sexually and asexually, and apparently can regenerate from a single segment (Berrill 1961)! In fact, when a new worm forms, it does not have any cephalic (aka. head) structures before it separates from its ‘parent.’ Asexual reproduction in annelids is not very common, and is generally relegated to smaller, colonial suspension feeders. Many aggregations of worms are actually a result of ‘gregarious settlement’ (larvae preferentially settle near members of their own species) rather than asexual reproduction. I would love to know more about this critter if anyone can drop some knowledge on me.


Berrill, N.J. 1961. Growth, Development and Pattern. Freeman, San Francisco, CA, USA.

Carlton, J.T. (editor). 2007. The Light and Smith Manual: Intertidal Invertebrates from Central California to Oregon, Completely Revised and Expanded. University of California Press, Berkeley, CA, USA.

Gilbert, D.S. 1975. Axoplasm architecture and physical properties as seen in the Myxicola giant axon. Journal of Physiology 253:257-301.

Nicol, J.A.C. 1948. The giant nerve-fibres in the central nervous system of Myxicola (Polychaeta, Sabellidae). Quarterly Journal of Microscopical Science 89:1-45.