Which phylum includes starfish and sea urchins?

Which phylum includes starfish and sea urchins?

• A. Cnidaria
• B. Mollusca
• C. Annelida
• D. Echinoderm

Answer: (D)

Starfish and sea urchins belong to the phylum Echinodermata. This group is defined by adults that exhibit radial (usually pentaradial) symmetry, a water vascular system that powers tube feet for movement and feeding, and a calcareous internal skeleton. They are marine animals and their larvae are bilateral, but they reorganize into radial adults. These features set echinoderms apart from other phyla like Cnidaria (jellyfish and relatives, with simple radial symmetry but no water vascular system), Mollusca (snails, clams, squids, often with a muscular foot and sometimes a shell), and Annelida (segmented worms with a bilateral body plan).

Starfish and sea urchins belong to the phylum Echinodermata. This group is defined by adults that exhibit radial (usually pentaradial) symmetry, a water vascular system that powers tube feet for movement and feeding, and a calcareous internal skeleton. They are marine animals and their larvae are bilateral, but they reorganize into radial adults. These features set echinoderms apart from other phyla like Cnidaria (jellyfish and relatives, with simple radial symmetry but no water vascular system), Mollusca (snails, clams, squids, often with a muscular foot and sometimes a shell), and Annelida (segmented worms with a bilateral body plan).