Wednesday, 29 September 2010

Dahlia Smith

My last post introduced the dahlia anemone (formerly Tealia felina but now Urticina felina). I've been trying to get more hard facts about this animal and as usual, because it isn't a bird, there's a scarcity on the internet- though I did unearthed this little gem.  The massive crude oil spill from the wreck of the tanker Torrey Canyon on the south coast in 1968 devastated the intertidal life (or maybe it was the detergent used to break up the oil).  One month after the spill, researchers found that the dahlia anemone was one of the most resistant animals on the shore, being commonly found alive in pools between the tide-marks which were completely devoid of all other animals. (I was very pleased to note that the person who published this research was called Smith. So that's the post title explained if you were wondering).

This photo shows the anemone with all of its tentacles retracted.  It has sticky projections on the outside which attract bits of debris and provide great camouflage.

After reading that they can deal with whole crabs, I wondered how.  Forget the web, my scruffy old 1961 reprint of a 1948 edition of  'Animals without Backbones' by Ralph Buchsbaum was more use.  Clearly no anemone is going to lift up its skirt and run after a crab so it just sits and waits until one blunders on top of it.  Then muscles contract to fold the tentacles inwards and pull the crab inside its insides.  Its structure is quite simple - basically just like a purse with a draw string top. Inside the animal there are a series of radial partitions and further sub-folds and along the edges of these are cells that release digestive chemicals.  Acidic in nature, they make short work of the calcareous external skeleton of the crab and hey presto - crab soup.  One hiccup later and the rubbish gets chucked out from the same orifice as the grub went in.  What could be simpler.

c/o Animals without Backbones: Ralph Buchsbaum: Penguin Books 1961

Meanwhile, not far away, I turned over a large stone and found this tiny thing clinging to a layer of sponge.  Can a squat lobster be cool? Absolutely. No more than about 5mm long in the body, it was the yellow socks that did it for me.  More on squat lobsters next time.


  1. Cracking posting.
    Have you read that other good book "People without backbones" ?

  2. I didn't want to read this as I regret not doing nearly enough rock-pooling this summer :(

    Caught a squat lobster myself this year: the colour scheme was navy blue and pillar-box red, have no idea what species though.

    Nice photos (and writing style, as ever) - most of my aquatic photos ended up with the dreaded flash reflection - arrrgh!

  3. Hi Theresa and thanks for your kind comments. By the sound of it your squatty was most likely Galathea strigosa, the spiny squat lobster. Just look at this for a fabulous photo :-

    I agree - rockpool photography is a bother without a camera that you can put under water. We also found a couple of sea hares but I failed miserably to get a decent shot through surface reflections.

    Best wishes, Allan