Within echinoderms, Ophiuroidea are most closely related to which group?

Within echinoderms, Ophiuroidea are most closely related to which group?

• A. Asteroidea (starfish)
• B. Cephalochordata
• C. Crustaceans
• D. Gastropods

Answer: (A)

This question tests evolutionary relationships within echinoderms. Ophiuroidea (brittle stars) are most closely related to Asteroidea (starfish) because they together form the clade Asterozoa, meaning they share a more recent common ancestor with each other than with other echinoderms. They also share key features typical of this group, such as a water vascular system with tube feet and pentaradial symmetry as adults, reflecting their close kinship. Crinoidea (sea lilies/feather stars) split off earlier in the echinoderm lineage, and Cephalochordata, Crustaceans, and Gastropods are not echinoderms, so they are much more distant relatives.

This question tests evolutionary relationships within echinoderms. Ophiuroidea (brittle stars) are most closely related to Asteroidea (starfish) because they together form the clade Asterozoa, meaning they share a more recent common ancestor with each other than with other echinoderms. They also share key features typical of this group, such as a water vascular system with tube feet and pentaradial symmetry as adults, reflecting their close kinship. Crinoidea (sea lilies/feather stars) split off earlier in the echinoderm lineage, and Cephalochordata, Crustaceans, and Gastropods are not echinoderms, so they are much more distant relatives.