The correct answer is (d) Limulus.
A living fossil is a species that has remained relatively unchanged for millions of years. Limulus is a horseshoe crab that has been around for over 450 million years. It is one of the few living members of the arthropod group Xiphosura, which also includes extinct species such as the sea scorpions. Limulus is found in shallow coastal waters around the world. It is a filter feeder and eats small organisms such as plankton. Limulus is an important part of the marine ecosystem and is also used in medical research.
Balanas is a barnacle that is found on the shells of whales and other marine animals. It has been around for about 150 million years. Daphnia is a small freshwater crustacean that is found in ponds and lakes. It has been around for about 50 million years. Sarcoptes is a mite that causes scabies. It has been around for about 10 million years.
Limulus is the only living fossil that is a member of the arthropod group Xiphosura. The other options are not members of this group.