Characteristics of Echinoderms
Deuterostome embryo development
secondary radial symmetry: larvae have bilateral symmetry (radial symmetry thought to have evolved from sessile forms)
five radial parts; sea urchins and cucumbers by folding “arms” upwards and fusing their edges; sea cucumbers lay on “side” and developed pseudo-bilateral symmetry, i.e. have distinct upper and lower side
Endoskeleton: calcite plates = ossicles, covered by epidermis, may be single plates (flexible body) or fused (solid shell, sea urchin)
Spines on calcite plates give “spiny skin” (phylum name!) sea urchin spines are endoskeleton and covered by thin skin!