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• Animals with bilateral symmetry can be divided into protostomes and deuterostomes based on the pattern of embryonic development. The deuterostomes are further divided into two phyla: Echinodermata and Chordata.
• Echinoderms are invertebrate marine animals that have pentaradial symmetry and a spiny body covering, a group that includes sea stars, sea urchins, and sea cucumbers.
• Chordata share five key characteristics that appear at some stage during their development: a notochord, a dorsal hollow (tubular) nerve cord, pharyngeal gill arches or slits, a post-anal tail, and an endostyle/thyroid gland

Echinodermata is the phylum that includes invertebrate marine animals. They do not possess the five key features that characterizes the chordates: a notochord, a dorsal hollow nerve cord, pharyngeal slits, a post-anal tail and endostyle. Hence, option (b). Echinodermata is the correct answer.

a. Cephalochordata

Chephalochordata includes members that possess the five main features that characterizes chordates during the adult stage: A notochord, a dorsal hollow nerve cord, pharyngeal slits, endostyle and a post-anal tail. Hence, option (a) is the incorrect answer.

c. Urochordata

Members of Urochordata during the adult stage do not possess a notochord, dorsal hollow nerve cord and post-anal tail. However during their larval stage they possess all of the five characteristic structures of chordates. Hence, option (c) is the incorrect answer.

d. Vertebrata
Members of the vertebrata display all the five characteristic structures of chordates during some point in their lifetime. Hence, option (d) is the incorrect answer.