Essay for May 2013: Corella
Previous essays were mostly devoted to summaries of scientific literature. In contrast, this one will describe an animal that lives on the Dock, but was just not mentioned in LOTD (there are hundreds of other animals in that catagory). The animal is a tunicate, similar to Ciona, but very different is some respects.
This tunicate is actually very common on the Dock in certain locations. It's common name is the Brooding Transparent Tunicate . It often forms clumps, and because it is smaller and more compact than Ciona, it is easy to ignore. According to Lamb and Hanby, eggs are released and then are trapped in the buldge of the exit siphon. There they are fertilized, presumidly by sperm that are sucked in through the intake siphon, escape entrapment by the feeding net, and then flow through the exit siphon. The eggs are claimed to be less dense than sea water because of a high concentration of ammonium chloride (replacing sodium chloride). The low density of the eggs is supposed to trap them in the exit siphon bulge undil they develop.
I haven't followed Corella tadpole development, but it is on my short list To Do for this summer. If I get some good images I will certainly share them with you.
Circulation of blood in the tunicate
Corella inflata is beautiful enough to justify this essay without any other attributes. However, it has at least two characteristics which make it ideal for the study of blood circulation (I don't remember if I told you in an earlier essay that this is now one of my passions). First of all it is transparent. Of course Ciona is also somewhat transparent, but you really have to cut away the tunic to see much detail of the heart and circulation. Corella is an order of magnitude more transparent.
Second, Corella is much more solid, it you poke it (or more important for me if you cut open the mantle) it contracts only very slightly. Thus if you need to see the heart or vessels in detail, all you need to do is gently cut open a window in the tunic. If you try this with Ciona, you need to pin it down at several points, and even then it contracts and distorts its entire body.
On the right you see Corella when illuminated from below. The intake siphon is at uper right, exit siphon top, stomach and gonads are the brown and yellow masses at bottom. You can see the faint grey grid that is the brachial basket. the heart is a slightly curved tube (in contrast to the sharply bent heart of Ciona. It lies along the upper ecge of the stomach and gonads, and is only a faint line in this image.
In the video below you see an animal in which fluorescent dye has been injected into the heart, specifically in the pericardial space. The actual heart volume is the empty space in the dye which moves along the heart tube to move blood into the circulatory network. In subsequent essays I will describe the blood flow through out the animal.
 Plate CH2, page 346, in Marine Life of the Pacific Northwest, Lamb and Hanby; 2005, Harbour Publishing, Madeira Park BC, Canada.