Sunday, June 26, 2011

Comb Jellies in the East River

Today I saw an animal I've never seen before. A comb jelly.

I was at a public educational program in Brooklyn Bridge Park in New York City called Seining the River Wild (Click here for details). A big group of kids showed up with their parents and everybody had a great time. (There’s another seining event coming up; you can click here to see the park's calendar of events.)

We met under the Manhattan bridge on the Brooklyn side, on a strip of sandy East River beach. We watched as scientists repeatedly waded into the water with seining nets to catch small wildlife, which was returned to the wild after everyone had a good look. They unfurled the nets on the shore to reveal algae, crabs, shells, shrimp, tiny fish (silversides, blue fish, flounder), and lots of little comb jellies.

I held a comb jelly in my hand for a moment. It felt like soft jello and seemed so insubstantial that I was afraid it would fall apart. But when it was released into a little tub of water its fine transparent structure appeared. Comb jellies don’t photograph well without some advance planning but you can see enough of one in the following photo to get an idea of it. It is that tangle of pale threads below and to the right of the handsome baby bluefish.

In the lower right corner -- a ghostlike comb jelly. Click on the photo to enlarge.

 The comb jelly is egg shaped and simple. It has a mouth at one end, an anus at the other, and a stomach in between. Its body is a jellylike mass with thin layers of cells inside and out, surrounding a hollow cavity. Most species are hermaphrodites that release sperm and eggs into the water where external fertilization occurs and jelly babies grow.
The comb jelly gets its name from long rows of plates that look like tiny combs. The combs are made of fused hair-like cilia; they beat back and forth to propel the jelly through the water. Comb jellies are the largest animals that use cilia to move. (The method is wildly popular among microorganisms.) The moving combs sometimes scatter daylight and look rainbow colored. Some species of comb jellies are bioluminescent and glow in the dark. 

Comb jellies are predators; they eat plankton and larvae, small crustaceans, and smaller jellies. The comb jellies we caught in the East River ranged from tiny to small; the largest was a wavy fluid inch or so long. They resemble jellyfish, but they are not, and they don’t sting.

Today’s comb jelly sighting was timely. The lowly comb jelly recently received a lot of press coverage when a scientific study identified comb jellies as the first animal group to branch off of the common evolutionary tree -- a position previously given to sponges. The change was based on a comparison of DNA sequences of many genes from many animals. Comb jelly DNA is least like that of other animals suggesting that comb jellies may have been the first animals on Earth. 

Nevertheless, just like my highly evolved self, comb jellies spend occasional Sunday mornings near the shores of the East River. 

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