GENERAL HISTOLOGY

Detailed explanation-1: -Echinoderms are deuterostomes and close relatives of chordates. Among echinoderms, only sea urchin embryos undergo asymmetric cell division at the 16-cell stage and form micromeres.

Detailed explanation-2: -Most of the deuterostomes belong to one of two groups that include the majority of its members–the echinoderms (the spiny skinned starfish, sea urchins, and their relatives) and the chordates (which include fish and other vertebrates).

Detailed explanation-3: -Echinoderms are coelomates that have a deuterostome pattern of embryo development. The same pattern of development occurs in the chordates.

Detailed explanation-4: -There are two groups of coelomate animals: protostomes and deuterostomes.

Detailed explanation-5: -The species of the phylum Echinodermata and the phylum Chordata are all deuterostomes. In the Introduction to Animals and Invertebrates chapter you learned that there are a number of differences between protostomes and deuterostomes, all having to do with their patterns of embryonic development.