The class Merostomata includes ancient marine arthropods whose only living representatives are horseshoe crabs. Their bodies are covered by a broad, protective shell and end in a long, pointed tail called a telson, while their appendages help them move, feed, and breathe. These animals first appeared hundreds of millions of years ago and have retained a remarkably similar overall body shape throughout their evolutionary history. Merostomes mainly inhabit shallow coastal waters, where they search sandy or muddy seafloors for food.