Still corals!

Ok, a short post today, as my last one was a bit heavy on the text, and I am not sure that is such a good idea.  I got a bit carried away with it, so will try to be more graphical in this one.

Last post was about corals spawning, so this one picks up with what happens after the mass release of sperm and eggs into the ocean.

After the eggs become fertilized, they develop into a larva known as a planula, which, to me, look a bit like some bacteria that you see under a microscope

A coral planula, or larva. Image from sciencesummit

Here is another picture, showing a coral planula alongside a Brittle Star larva

Coral Planula (left) with a brittle star larva. Image from

The final two images of  planulae are probably my favourite, they show the zooxanthellae (micro-organisms which live in symbiosis with the coral, more about that later!) already within the larva.  These are present in the egg when released by the colony!  The first image shows the egg with zooxanthellae inside it, and the second shows the larva.

Coral egg, the zooxanthellae are in the lower half of the picture. Image from

Coral larva. Image from

These larva float in the water column, until they land in a suitable place, such as on a rock, or a wreck of a ship. They do have cilia (From the Latin for eyelash, these are small  hair like structures which beat rhythmically), which can propel them within the water column, but they are not free-swimming in the way that larger organisms are.

Once they find a suitable place to settle (assuming they are not eaten by predators, as many of them are), they develop into polyps. This is the same type of polyp as the non-moving (non-motile) stage that all Cnidaria have.

Diagram of a coral polyp, image from wikipedia

Orange Soft Coral polyp, image from world oceans 

Next post will cover the development of polyps within a reef, and how different types of corals co-exist, as well as some surprising habits of corals!


3 thoughts on “Still corals!

  1. Pingback: When corals attack! « skepticalsquirrel

  2. Pingback: Recap « skepticalsquirrel

  3. Pingback: Corals and Starfish | Skeptical Squirrel

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