To solve this problem, we need to understand the concept of radial symmetry in different phyla.$\newline$Radial symmetry is a type of symmetry where body parts are arranged around a central axis.$\newline$Let's analyze each option:$\newline$• Option 1: Ctenophora$\newline$ - Ctenophores, also known as comb jellies, exhibit radial symmetry.$\newline$• Option 2: Hemichordata$\newline$ - Hemichordates, such as acorn worms, exhibit bilateral symmetry, not radial symmetry.$\newline$• Option 3: Coelenterata$\newline$ - Coelenterates, which include cnidarians like jellyfish and corals, exhibit radial symmetry.$\newline$• Option 4: Echinodermata$\newline$ - Echinoderms, such as starfish and sea urchins, exhibit radial symmetry in their adult form.$\newline$From the analysis, we see that radial symmetry is not found in adults of phylum Hemichordata.$\newline$Therefore, the correct option is Option 2.