An EntityArchetype is a unique array of ComponentType. EntityManager uses EntityArchetype stucts to group all entities using the same component types in Chunks.
// Using typeof to create an EntityArchetype from a set of components
EntityArchetype archetype = EntityManager.CreateArchetype(typeof(MyComponentData), typeof(MySharedComponent));
// Same API but slightly more efficient
EntityArchetype archetype = EntityManager.CreateArchetype(ComponentType.Create<MyComponentData>(), ComponentType.Create<MySharedComponent>());
// Create an Entity from an EntityArchetype
var entity = EntityManager.CreateEntity(archetype);
// Implicitly create an EntityArchetype for convenience
var entity = EntityManager.CreateEntity(typeof(MyComponentData), typeof(MySharedComponent));