Leatherback and Marine turtle

Leatherback noun - Wide-ranging marine turtle with flexible leathery carapace; largest living turtle.

Marine turtle and leatherback are semantically related. In some cases you can use "Marine turtle" instead a noun "Leatherback".

Marine turtle noun - Any of various large turtles with limbs modified into flippers; widely distributed in warm seas.

Leatherback and marine turtle are semantically related. Sometimes you can replace term "Leatherback" with "Marine turtle", this terms are similar.