Limulus belongs to which of the following classes?
A) Insecta
B) Merostomata
C) Crustacea
D) None of the above

Hint: Class is the taxa higher than that of family and lower than that of order. Limulus is a genus and in order to find the class, it's important to know the family the genus belongs to.

Complete answer:
1) All the classes given in the choices belong to phylum arthropoda. ClassInsecta includes all insects. Insects have three main body segments: the head, thorax and abdomen. They have six legs, one or two pairs of wings and specialized mouthparts.
2) Class Merostomata is a class of subphylum Celicerata. They include extant horseshoe crabs and extinct sea scorpions. living fossil limulus.
3) Class Crustacea has its origin from the Latin crusta, which means shell. Crustaceans are a very diverse group of invertebrate animals which includes active animals such as the crabs, lobsters, shrimp, krill, copepods, amphipods, and more sessile creatures like barnacles.
4) The genus limulus belongs to the family limulidae, which comes under the Class Merostomata.

Additional Information:The genus limulus has just one extant species, the Atlantic horseshoe crab (Limulus polyphemus). These species play a major role in the local ecosystems. Their eggs provide an important food source for many species such as shorebirds. The younglings and adults are a food source for species like sea turtles. Many other fossil species of the genus limulus are known (like Limulus coffin, Limulus Darwin), many of which have since been assigned to other genera later on.

Thus, the correct answer is optionB (Merostomata).

Note:To find the class of any genus/species, identifying its phylum and the family provides much better insight into the taxonomy, hence makes it easier to find the class.