4. How can the endoskeleton
of echinoderms be
characterized in comparison
to analogous structures
present in vertebrates,
arthropods and molluscs?

Gap-fill exercise

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The echinoderm skeleton internal,
i.e., it an endoskeleton. It made of
calcium (calcareous).

Vertebrates also internal skeleton
made bones and cartilages.
have an external
made of chitin, chitinous exoskeleton.
Some present a calcareous
that works as .