Sea Urchin Embryology: 3 different stages.

The development of a sea urchin is a representation of animal development and similar stages occur in in all animals from the hydra. When the sea urchin embryo divides, the cell becomes smaller, until it is in the blastula stage (1st). By the time they hatch from their eggs they can barely be seen when magnified. A sea urchin comes from the Phylum: Echinodermata, and is on the left side of the my tree diagram, it is a Deuterostome. 
The first stage we looked at was a unfertilized egg, second was a fertilized egg, and third was gastrulation. 

We quite obviously skipped a few steps in our lab, so if it were in the proper order it would go like this:

1-Unfertilized Egg

2-Fertilized Egg

3-Two celled stage

4-Each cell divides

5-Four celled stage

6-Eight celled stage

7-Blastula, hollow ball

8-Gastrulation, 2 layers

The photos here a the cell stages we looked at today in class.