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Pyrosomes: underwater UFO strikes a nerve cord

Those of you who have made contact with an extraterrestrial being at one time or another likely agree that the experience was completely unexpected. That is exactly how I felt when on a dive some years ago I saw this “thing” hanging in the water column.It was a hoPyrosomes typically hang suspended in the water column. They are stealth travelers, using tiny hairs found within the hollow tube to propel themselves. c.TideLines.orgllow lavender tube with a bumpy, plastic-like texture. To say I had to work hard to catch up to it would be a cosmic overstatement. At first it appeared to be nothing more than a piece of flotsam until I noticed tiny hairs beating furiously inside the hollow. Where is NASA when you need verification?

It turns out that, as with most UFOs, there was a reasonable explanation for my paranormal sighting. The creature in question is a pyrosome (Pyrosoma atlanticum), a colonial animal (many individuals bound together to look like one) that holds membership in the subphylum tunicata. Pyrosomes construct barrel-shaped colonies that float through the water, growing in excess of 30 feet in some parts of the world’s ocean. However, from my literature search, pyrosomes found off our coast are seldom larger than an ear of corn, which my experience concurs. Since then, I have infrequently stumbled upon more pyrosomes that were no more than a couple of inches in length. 

In regards to lifestyle, pyrosomes exploit the open sea as a habitat. The colony propels itself through the water by means of cilia (those tiny hairs) that pump water through the bodies of the individuals that make up the barrel. When fueled by mechanical, chemical, or light stimuli, the sophisticated colony moves or may create spectacular bioluminescent displays. 

You practical folks may be wondering, “What good are these prototypes of a Star Trek space vehicle?” Though they are a human food source on some Pacific islands, their economic impact is negligible. But bear in mind that every web-of-life member is important in the big scheme because having diversity of life is not only the spice of life but results in a stable ecosystem. Anemones, sea stars, various marine snails, and even some inshore fishes are most happy to see these critters on the menu whenever they are in season. And because pyrosomes feed by filtering copious amounts of water as a way to capture nutritious particles and organisms, they make great oceanic purification systems. Aside from improving visibility, pyrosomes may concentrate toxic materials and so be useful indicators of nearshore pollution.

As to how such bizarre-looking creatures came to be is still up for speculation. Generally, tunicates are considered the earliest vertebrate models (they are in the phylum chordata, just like us!). They swing between the invertebrate and vertebrate sides of the fence because they have features of both. On the invertebrate side, they are filter feeders and lack a backbone. On the vertebrate side, they have a primitive spinal cord and a nerve cord, which connects to a simple brain. The pharynx (throat) develops gill slits on each side and has what is considered to be a forerunner of the vertebrate thyroid gland. Some of these characteristics are seen in vertebrates during embryonic stages (like in humans), but other features are seen in the developed vertebrate animal (like gills in fish). 

Whatever is our common heritage with these critters (they brought their nerve cords to the evolutionary party some 570 million years ago), a wide gulf separates us today since they are for the most part deeply committed to a life in the sea. Considering our close connection with the otherworldly pyrosomes, it is humbling to see how far we have evolved, at least physically and physiologically.

— Judith Lea Garfield, naturalist and underwater photographer, has authored two natural history books about the underwater park off La Jolla Cove and La Jolla Shores. Send comments to jgarfield@ucsd.edu.