Harp seal and True seal

Harp seal noun - Common Arctic seal; the young are all white.

True seal and harp seal are semantically related. In some cases you can use "True seal" instead a noun phrase "Harp seal".

True seal noun - Any of several seals lacking external ear flaps and having a stiff hairlike coat with hind limbs reduced to swimming flippers.

Harp seal and true seal are semantically related. Sometimes you can replace phrase "Harp seal" with "True seal", this phrases are similar.