Over the past few months, Oregon beachcombers have discovered something odd blanketing their beaches.
These are animals are pyrosomes (literally, “fire bodies”) and they light up like the Vegas strip in the dark, according to reports dating back to at least T.H. Huxley.
As reported in The Washington Post and on a NOAA blog, research cruises by NOAA fisheries have encountered unusually large numbers of the organisms off Oregon since last winter. A submerged camera revealed an oceanscape thick as thieves with the normally rare organisms. Scientists speculate that warming oceans brought on by climate change may somehow be the cause, since pyrosomes are known to favor warm surface water.
What may come as a bigger surprise, however, is that in spite of their deeply alien appearance, these creatures are actually pretty close relatives – much more closely related to us, in fact, than jellyfish, corals, siphonophores (whose lifestyle is very similar), insects, crustaceans, mollusks or even starfish and sea cucumbers. How?
Pyrosomes are actually colonies of animals called tunicates. A solitary tunicate appears a bit like a swollen, sometimes lurid heart.
The cardiac analogy is more than skin deep because a tunicate, like a heart, is all about pumping fluid. Tunicates scour the currents for the tastiest bits of flotsam, sucking the water in through their incurrent siphon and ejecting it through an excurrent siphon. In between siphons lies a basket-like filter (the pharynx) that traps all that planktonic goodness for a tunicate’s feeding pleasure, allowing water to escape into the larger chamber that contains the basket, the “atrium” (in a human we would call it something like "body cavity"). The flow of water is powered by beating tails on the cells of the basket/pharynx. When they feel like it, tunicates can also contract body wall muscles to eject a pulse of water, hence their alternative name, “sea squirt”.
But this grotesque – to vertebrate tastes, anyway – creature has a larva that looks very like a tadpole. Here's a 1901CK image demonstrating the resemblance (tunicates are also called "ascidians".)
Inside this more comfortingly-shaped larva (that only swims for a day or so before settling down) is a hollow nerve cord, like so:
Beneath it is a stiff but flexible notochord, a much simpler version of our backbones. And the larva also has pharyngeal slits, a feature found throughout the chordates and vertebrates. Of these features, the adults retain only a small portion of the nerve cord and the pharyngeal slits, which become the basket-like pharynx the animal uses to feed and breathe. Although they are not vertebrates, tunicates are thus the next closest thing: chordates.
Now imagine if you glued a bunch of barrel-shaped tunicates together into a hollow tube. Add a band of muscles around the midsection of each individual that allows it to jet water to the interior of the tube for general propulsion. Now electrify them. BAM -- you've got a pyrosome, more or less.
And not all pyrosomes are cute and petite like the ones off Oregon. Some are titans.
Yet for the enormity of the colony, the individuals within it are not especially giant and may be downright tiny, ranging from 10 inches to just a few millimeters. The giant pyrosome, Pyrosoma spinosum, can reach 33 feet long and may be big enough that a person can fit inside it – yet the individuals within it are only about 1 inch long. When touched, a wave of light may ripple along the colony.