There are over 20,000 species of fish, divided into three groups: bony fish, cartilaginous fish, and jawless fish. Bony fish, which are the most numerous, have skeletons of bone, and swim bladders (gas filled organs) to keep them afloat. Cartilaginous fish, such as sharks, rays, and rat fish, are mostly marine hunters; they have skeletons made of cartilage, and sandpaper- like skin, The primitive jawless fish have sucker-like mouths, and include lampreys and hagfish.
 |
| Anatomical directions and axes |
No comments:
Post a Comment