Cool animals: Ctenophora and Cnidaria

December 1, 2012 • 1:05 pm

Earlier this week I reported having read Peter Holland’s lovely little book, The Animal Kingdom: A Very Short Introduction, which is larded with interesting facts about animals.  I highlighted some of them on the plane home, intending to check them out when I was back. And of course the facts did check out (the VSI guides are very reliable).  Today I’ll put up a few bits about the phyla  Ctenophora (comb jellies) and Cnidaria (jellyfish, coral, and sea anemones).

Ctenophores are some of the coolest animals around. They’re jewels of the sea, small transparent beasts of amazing shape and behavior. Some of them, as seen in the second video below, can pulsate with flashes of multicolored lights, like a neon sign flashing outside a diner (for many pictures of ctenophores, go here.)

One of Holland’s descriptions struck me, and made me want to look at the animal:

The best-known comb jellies are the grape-sized “sea gooseberries” such as Pleurobanchia found throughout Pacific and Atlantic oceans, and around the British coast.  But the most spectacular comb jelly is undoubtedly the giant 1-metre-long Cestum veneris, or Venus’s girdle, named after the Roman goddess of love. Instead of the usual egg-shape typical of ctenophores, this striking, iridescent animal has an elongated, ribbon-like body that shimmers in the sea as the sun’s rays are scattered by its rows of cilia. In Richard Dawkins’s words,Cestum is “too good for a goddess.”

Of course I wanted to see it, and found a video of the goddess from YouTube. The true beauty of this creature is seen beginning about 30 seconds in:

Here are more ctenophores; they’re amazing!

Another observation about jellyfish (Cnidaria) intrigued me:

Many rhizostomids [jellyfish in the order Rhizostomae, which has many mouths instead of a single one like many jellyfish], such as Mastigias papua, supplement their food intake by harbouring in their tissues millions of symbiotic algae capable of producing energy by photosynthesis.  This enables Mastigias to live at incredibly high densities. In “Jellyfish Lake” on the Pacific island of Eil Malk in Palau, intense aggregations of Mastigias papua can sometimes reach a thousand 6-centimetre animals per cubic meter of sea water.

Of course I found that hard to believe—such densities! But I checked it out and it’s true (well, I can’t verify the density figure). Here’s a video of Jellyfish Lake:

And a photo of the lake and a diver from echeng on Flickr:

14 thoughts on “Cool animals: Ctenophora and Cnidaria

  1. Here’s as good to ask the question as any place: Does anyone know more about Berthold Hatschek, the guy who coined the termini Cnidaria and, I think, even Ctenophora? (Beyond the post-WW2 biography by Otto Storch, and the available publications, that is. I wanted to check the archive of the Natural History Museum in Vienna last time, but didn’t have the time.)

  2. When I was in the Philippines I wanted to visit this lake but it’s not easy to get to, so I didn’t make it. Maybe I should have tried harder.

    1. While I was watching the videos, I realized that this is basically as close as I’ll ever get to those amazing beasties.

      At least you got to go to the Philippines….


  3. I’m a bit dubious about the assertion in the second video, the Plankton Chronicles one, that Ctenophores don’t have stinging cells. I clearly recall swimming through clouds of these on one occasion in the North Sea and feeling my lips going numb and slightly “tingly” as I snorkelled through the cloud. Since then, when I’ve seen them, I’ve admired them (they are very pretty), but kept a little bit more distance.
    What does Wikipedia say … hmm, Colloblasts are “sticking” cells rather than “stinging” cells. But some ctenophores are known to extract entire “stinging” cells from eaten jellyfish and use them as weaponry. So, maybe I encountered some of them ; or maybe I was paying so much attention to the Sea Gooseberries that I didn’t notice jellyfish in the same area.

  4. Just to pick a nit . . . in the last sentence of your first paragraph, you meant to write phyla, not phylum. This is why we no longer have Coelenterata… 😀

    1. we no longer have Coelenterata

      Not as a phylum, maybe, but recent molecular-phylogeny studies suggest that they are each others’ closest relatives (though not very close, it’s true) and belong in their own clade that could be called Radiata or Coelenterata.

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