Getting to know three … Echinoderm edition

Sure you know that some animals are related to one another. Often though it’s difficult to pinpoint their similarities.  Well, on the third day of every month I am going to explain three features that are common among the animals of a certain group. Each group generally has more than three representatives, but I am going to choose three to keep it simplified.

To get us started … Have you ever thought about what a sea urchin, sea star, and a sand dollar have in common? Among others in this group those three animals are in a phylum of marine animals know as the echinoderms. Sea cucumbers and brittle stars are also well-known echinoderms. Check out the image below to learn what these animals all have in common.

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How does a sea star move?

I came across this image of a dissected sea star and had to share it. It does a great job of identifying intricate details of the sea star physiology that are involved with the locomotion and vascular system of the invertebrate.

The vascular system is part of the circulatory system that helps  transport nutrients back and forth across the animal’s body. These echinoderms (a group of marine invertebrates known for bumpy skin and radial symmetry, including sea stars, sea urchins, and sand dollars) begin the movement of their tubed feet with water entering through the madreporite. The madreporite is the wart-like, red or yellow opening in the center of the sea star. It acts like a  pressure-equalizing valve. Next, the water will circle around the stone canal to be distributed to the arms of the sea star. At this point, water goes to the tubed feet and being the act of moving by contracting and stretching. Tubed feet also come in handy when grasping food to place into the mouth of the sea star. For more information and a great image of the madreporite of a sea star click here.

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