Which term describes a marine plant that forms beds in shallow coastal waters?

• A. Agnatha
• B. Unicellular Algae
• C. Sea Grass
• D. Thallus

Answer: (C)

Sea grass describes a marine plant that forms beds in shallow coastal waters. These are flowering plants (angiosperms) that live submerged, rooting in sediment and growing to form extensive underwater meadows known as seagrass beds. They’re rooted, photosynthesize underwater, and create habitat, stabilize sediments, and influence water clarity, which is why they’re the classic term for these bed-forming marine plants. The other options don’t fit: jawless fish aren’t plants; unicellular algae aren’t true plants and don’t form the persistent, wide-ranging beds seagrasses make; and a thallus is the body form of many simple algae or non-vascular organisms, not the specific plant type that creates seagrass beds.