“My Strangest Relative”
(an exercise from recent creative writing class)
My strangest relative is the sea tulip, also known as a sea squirt, tunicate, and ascidian. I see hundreds of them cast up on the seashore after a big blow on the Southern ocean. It was only when I enrolled in a biology class at Massey University that I discovered we were related. This is pretty amazing to me as they look rather like a wrinkly potato with a rope attached. As it turns out, they have a primitive sort of backbone called a notochord. Well at least the baby does. Like a tadpole, it metamorphoses later into the strange body I see on the seashore.
Talking of tadpoles, it turns out that you and I - everyone - has gone through a stage when we had something like a tail. In the human case it is re-absorbed into the vertebrae after about four weeks.
Indeed if you look at comparative images of early development of animals - from my cousin the sea tulip, through fishes, to salamanders, pigs and humans, - you couldn’t tell them apart.
The other strange aspect of the sea tulip is that its outer layer is made of cellulose, heavy and leathery, rarely encountered in animals. One more odd thing: the blood of some species contains large amounts of vanadium, up to 10 million times the concentration in the ocean. Vanadium is a metallic element we use in the hardening of steel. No-one knows yet why sea squirts have it.
They also drink a lot more than I do. My textbook relates a specimen was recorded circulating 173 litres of water in 24 hours. I can manage maybe 3, if I include tea, coffee and wine.
Apart from these oddities, the tunicate is just like us. It has an entry point for food, an exit point for waste, a digestive system with stomach and intestine, and gonads. Oddly, the heart periodically reverses the flow of blood. It doesn’t seem to need a brain though it does have a nervous system.
You’d think this distant cousin of mine couldn’t teach us humans much, but it is still a mystery how and why it collects vanadium in its blood. Given that we use a lot of this metal we have at least one avenue of enquiry.
I doubt that we have any reciprocal use to them.
CJM July 2012