In the sand tiger shark, the most developed embryos eat their siblings in the womb, so each female gives birth to only one or two pups per litter. This very low reproductive rate makes the species extremely vulnerable to overfishing.
What defines this group — Sharks & Rays
The cartilaginous fish: not a single bone in the body, a skeleton made entirely of cartilage.
A cartilage skeleton, lighter and more flexible than bone.
No gill cover: five to seven gill slits open on the sides or underneath.
Pores on the snout — the ampullae of Lorenzini — pick up the electric field of prey.