Echinoderms have no hydrostatic skeleton. This is reserved for organisms such as Cnidaria, Ctenophora, Trematoda, Annelida, etc., who use muscular pressure as a support. Echinodermata use mutable connective tissue and ossicles for structure and support. Tube feet are unique to the phylum Echinodermata. So is the water vascular system that they are a part of.
Maybe you could answer a stupid question for me, galleon...if the mesoderm in echinoderms forms the exoskeleton, what exactly does the ectoderm become?
Maybe you could answer a stupid question for me, galleon...if the mesoderm in echinoderms forms the exoskeleton, what exactly does the ectoderm become?
Hey Matt, The calcified ossicles of echinoderms are considered a true endoskeleton (in fact, the Crinoids have true vertebrae). The ectoderm covers the mesoderm and the ossicles, as a skin-like layer. Most contemporary urchins even have spines (which are modified ossicles) at least mostly covered in ectoderm. So, if you have an urchin that looses a spine, its an open flesh wound.