10 Surprising Animal Pairs You Didn’t Realize Are Close Relatives

10. Sea Stars and Sea Urchins: Echinoderm Enigmas

Sea stars and sea urchins, with their radial symmetry and spiny skin, are members of the phylum Echinodermata. This group, which also includes sea cucumbers and brittle stars, is characterized by its unique water vascular system and calcareous endoskeleton. Despite their differences in form and function—sea stars are known for their ability to regenerate lost limbs, while sea urchins are often covered in protective spines—both share a common evolutionary heritage. Their kinship is evident in their similar larval forms and developmental patterns, reflecting their shared ancestry. The sea star-sea urchin connection highlights the evolutionary history of echinoderms, a group that has thrived in marine environments for over 500 million years.