Provide a named example of Subclass Elasmobranchii and list key features that would be annotated in a diagram.

As an AI, I cannot draw diagrams. However, I can provide a named example of Subclass Elasmobranchii and list key features that would be annotated in a diagram.

A named example of Subclass Elasmobranchii is the Spiny Dogfish (Squalus acanthias).

An annotated diagram of a spiny dogfish would typically include labels for the following external features:

• Snout
• Mouth (ventral)
• Nares (nostrils)
• Eyes
• Spiracles
• Gill slits (5 pairs)
• First dorsal fin (with spine)
• Second dorsal fin (with spine)
• Pectoral fins
• Pelvic fins
• Caudal fin (heterocercal tail)
• Lateral line
• Claspers (in males)
• Cloaca