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Friday, January 11, 2013

When is a bubble not a bubble?

Although bubbles commonly remain on the surface at the edge of receding waves, in mid-winter it's worth checking closely as some of the bubbles may not be bubbles!

Some of them might be ctenophores, also known as comb jellies.  Compared with beach bubbles, these gelatinous animals are completely spherical, thicker, and when seen well, contain pale lines running from pole to pole.  They'll also hold their shape when you pick them up, like soft, clear marbles.

It was interesting to notice how the sunlight glowed around them.  Once I realized they were washing ashore, I started looking for these illuminated orbs on the sand.  

[Note: The type of sand in these photos — fine-grained, with lots of shell material — is a clue to the location = Doran Beach].

If you focus carefully, sometimes you can see the pale lines running pole-to-pole, similar to longitude lines (or meridians).  These lines contain parallel rows of "combs" that the comb jelly uses for locomotion.

This type of comb jelly is sometimes called a sea gooseberry (Pleurobrachia bachei).  Most of these individuals were quite small, less than 10 mm long.  I also found one that was only ~4 mm long.  I placed it next to a larger one for scale.  Can you spot it in the picture below?

I first introduced sea gooseberries last February.  Click here to learn more about them and see what they look like when swimming in the water.

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