Complex sentence: They are in the fish subclass Elasmobranchii, along with sharks.They are closely related to sharks, from which they can be distinguished by their flattened bodies, enlarged pectoral fins that are fused to the head, and gill slits that are placed on their ventral surfaces.
Split into simpler sentences: They are in the fish subclass Elasmobranchii, along with sharks, to which they are closely related. Rays are distinguished by their flattened bodies, enlarged pectoral fins that are fused to the head, and gill slits that are placed on their ventral surfaces.