Sea turtle and Turtle

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

Turtle and sea turtle are semantically related. In some cases you can use "Turtle" instead a noun phrase "Sea turtle".

Turtle noun - Any of various aquatic and land reptiles having a bony shell and flipper-like limbs for swimming.

Sea turtle and turtle are semantically related. Sometimes you can replace phrase "Sea turtle" with "Turtle", this terms are similar.