Fish with skeletons not made of bone?

You're thinking of cartilaginous fishes! These are a group of fish that have skeletons made of cartilage, not bone.

Here are some examples of cartilaginous fishes:

* Sharks: Think great white sharks, hammerhead sharks, and many others.

* Rays: This includes stingrays, manta rays, and eagle rays.

* Chimaeras: Sometimes called "ghost sharks," these fish have a more elongated body shape than sharks or rays.

Key differences between cartilaginous fish and bony fish:

* Skeleton: Cartilaginous fish have skeletons made of cartilage, which is a flexible and strong tissue. Bony fish have skeletons made of bone, which is harder and more rigid.

* Gills: Cartilaginous fish have five to seven gill slits on each side of their head. Bony fish have a single gill opening on each side of their head.

* Scales: Cartilaginous fish usually have placoid scales, which are small, tooth-like structures embedded in their skin. Bony fish typically have bony scales, which are thin, flat, and overlapping.

Let me know if you have any other questions!