Gastrula of an Echinoderm
click image to see the next echinoderm
The development of echinoderms is very interesting. When the eggs develop into a so-called gastrula you can see the anus being formed from the opening. This is quite amazing since in most multicellular creatures without a backbone the mouth is formed from this opening. In fact the kingdom of animals can be separated by this stage in the larval development into two groups, the deuterostomes and the protostomes (mouth first). Together with the chordates the echinoderms belong to the deuterostome branch of the animal kingdom. This means that echinoderms are more related to us humans than you might think.
Since all these gastrulas look alike it is not yet possible to determine whether this is becoming a starfish, sea-urchin of other echinoderm.
image © Wim van Egmond
size about 0.25 mm.
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