Question

Which of the following animals is a ‘living fossil’?
A) Limulus
B) Neopilina
C) Both A and B
D) None of the above

Answer 1

Hint: Limulus is also known as horseshoe crab. Neopilina belongs to the class of Monoplacophora. Limulus and Neopilina both existed around 400 to 500 years ago. Many species of the Limulus and Neopilina currently exist.

Complete answer:
Living fossils is the term coined by Charles Darwin. It is used to describe the living creatures that have remained largely unchanged for millions of years. Living fossil is called a living species of the organisms that appear to be similar to a species.
Horseshoe crab (Limulus) includes marine arthropods which belong to the family Limulidae and order xiphosura. They are mostly found in soft sandy or muddy bottoms around shallow ocean water. Their origin was found 450 million year ago. They are considered as the living fossils. They have not undergone obvious morphological changes in comparison with carboniferous and Triassic fossil forms.
Neopilina shows a close relationship with fossils that existed about 400 to 500 million years ago. It is a bottom feeder. It was found that cephalopods evolved from the Monoplacophora. They have an order of Tryblidiida.
From this we know that both the Limilus and Neopilina are living fossils.

Therefore, the correct answer is option C.

Note: Limulus polyphemus, Limulus coffin, Limulus priscus and Limulus woodward are some currently valid species of genus horseshoe crab. Limulus polyphemus is an Atlantic horseshoe crab. It is also called king crab. These are not really meaty, but their roe can be eaten. It tastes like briny rubber. Neopilina bruuni, Neopilina galatheae and Neopilina re bainsi are some species of Neopilina.