Would you believe me if I told you that these blob-like animals are more closely related to vertebrates (like ourselves) than to most other invertebrates?
When I caught a glimpse of one of these guys in the Aqualab at the University of Guelph, my first thought was there’s no way that this animal is related to me!
So what are they?
At first glance they may resemble a sea sponge, or coral… but in fact they are Tunicates, or more commonly known as ‘Sea Squirts’.
So how on Earth is something that resembles a sea sponge related to a human?
I decided that I was going to come to the bottom of this, and that I needed to do some further investigation into these mysterious creatures.
Where do they fit in?
Tunicates are part of the phylum Urochordata, closely related to the phylum Chordata that includes all vertebrates. You may be thinking to yourself… What traits could these animals possibly share with humans? The answer is found by taking a closer look at their tadpole-like larva (below).
As you can see, the Tunicate larva contains the traits that are apparent in all Chordates, even you and me! (Even though as adults they may seem more like the cousins of the sea cucumber). Because of these close ties, there is a considerable amount of research being done, such as in Delsuc et al. 2006, to try and learn more about their development and their genetic relationship to other animals.
Never far from home
So how is it that these guys ended up developing into something so different from us?
The answer can be found by taking a look as their lifestyle. Most adult tunicates are sessile and attached to rocks or any other suitable substrate, and they will stay there all of their life (Delsuc et al. 2006). Because of this sedentary lifestyle, adult Tunicates have no need to have complex sense organs, or even a brain for that matter!
They have successfully developed a way to survive and gain food without ever having to leave their home (if only we were so lucky!).
They in fact use a form of feeding that is called suspension feeding. This allows them to capture suspended particles and plankton by filtering sea water in through one siphon (incurrent), through the pharyngeal slits, then out via the excurrent siphon.
The Battle for Space
With approximately 3000 different species of Tunicates, these guys are sure to be good at holding their ground. In a study done by Clark et al. 2012, it is seen that there are several invasive species in Prince Edward Island that may be causing havoc on the local aquaculture industry by fouling mussel socks, aquaculture gear, boat hulls and wharves. They are currently searching for ways to prevent the populations from getting out of hand…because once it is, it can be incredible difficult to control.
A bright Future
Although there is still a lot of work to be done, researchers have found that several chemical compounds produces by certain species of Tunicates have anticancer properties (Iglesias et al, 2012).
My question is, what properties do these compounds have that gives them the potential to ward off this disease? And how long will it take to be able to effectively find a cure?
These questions will hopefully one day be answered, with the help of our distant relatives.
Delsuc, Frédéric, et al. “Tunicates and Not Cephalochordates are the Closest Living Relatives of Vertebrates.” Nature 439.7079 (2006): 965-8. ProQuest Agriculture Journals; ProQuest Psychology Journals. Web. 8 Oct. 2012.
Iglesias, C., and J. Guinea. Aquaculture of Tunicates Producing Anticancer Compounds:
Reproduction and Larval Development of Ecteinascidia Turbinata (Phlebobranchia Perophoridae)., 1995. Biological Sciences. Web. 8 Oct. 2012.
Stewart-Clark, Sarah. “Molecular Assays for the Detection of Invasive Tunicates and Phylogeography of a Tunicate Invasion in Prince Edward Island.” University of Prince Edward Island (Canada), 2010. Canada: ProQuest Dissertations & Theses A&I.Web. 8 Oct. 2012.