Sea urchins undergo radial cleavage, as do "typical" deuterstomes, such as chordates, ascidians, and other echinoderms. Like embryonic cleavages in other organisms, sea urchin cleavage divisions are reductive, i.e., the cleavages result in more cells, but without an increase in the total cellular volume of the embryo.

Do echinoderms have spiral cleavage?

Deuterostomes are animals that share such embryological similarities as radial, indeterminate cleavage and a blastopore that becomes the tail end. Echinoderms (starfishes, crinoids, sea urchins, and their relatives) are often radially symmetrical as adults, but their embryonic stages show similarities to the chordates.

Do echinoderms and chordates have radial cleavage?

chordates and echinoderms are deuterostomes, so they have radial cleavage and they have formation of the mouth at the end of the embryo opposite the blastopore. -chordates have a notochord, dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail.