Which lineage of Echinoderms is made up of about 950 species of sea urchins and sand dollars, which have their ossicles fused into solid tests that restrict flexibility but provide excellent protection?

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The lineage of Echinoderms consisting of sea urchins and sand dollars is called Echinoidea. These organisms have their ossicles fused into solid tests, which restrict their flexibility but provide superior protection. There are around 950 species of sea urchins and sand dollars in the Echinoidea lineage.

Which Lineage of Echinoderms Is Made Up of About 950