The largest ever members of this phylum are called eurypterids and lived in the Paleozoic era. Sections of their bodies are called tagmata. Some members of this phylum have a circulatory system with a fluid termed hemolymph, and they grow through a process called ecdysis. An extinct subphylum in this phylum dominated the ocean from the Cambrian to its extinction in the Permian and are named for the three lobes in their lateral symmetry. For 10 points, identify this phylum whose subphyla include 
The largest ever members of this phylum are called eurypterids and lived in the Paleozoic era. Sections of their bodies are called tagmata. Some members of this phylum have a circulatory system with a fluid termed hemolymph, and they grow through a process called ecdysis. An extinct subphylum in this phylum dominated the ocean from the Cambrian to its extinction in the Permian and are named for the three lobes in their lateral symmetry. For 10 points, identify this phylum whose subphyla include Chelicerata, Trilobita, and Crustacea, characterized by a hardened exoskeleton made of chitin.
The largest ever members of this phylum are called eurypterids and lived in the Paleozoic era.
arthropoda