Question

How do crustaceans differ from arachnids?

Answer 1

Hint: Arachnid and crustaceans belong to the phylum Arthropoda. Arachnid and crustacean are invertebrates which have similar body structure. They have exoskeleton, jointed legs and segmented body. An example of crustacean is crab and that of arachnid is spider.

Complete answer:
Phylum Arthropoda consist of organisms which have chitinous exoskeleton, book lungs, appendages, antenna, compound eyes and endocrine system. The five major groups are Arachnida, Crustacea, Chilipoda, Diplopoda, Hexapoda.

Let us discuss the difference between arachnids and crustaceans.

Arachnids	Crustaceans
The body is divided into two parts: the prosoma or the cephalothorax and the opisthosoma called the abdomen.	The body division is called the cephalothorax and the abdomen.
The cephalothorax does not have any enclosure.	The shield like carapace enclosing the cephalothorax is present.
The appendages are connected to the prosoma.	The appendages are found on all the body segments.
All arachnids are terrestrial.	All crustaceans are aquatic.
Over 60000 species are known so far.	Over 30000 species are found so far.
They are less than 5 cm in size.	They are relatively larger in size.
The appendages are used for walking.	The appendages are used for swimming or eating food, crawling.
The excretion occurs through coxal gland.	Excretion occurs through green glands.
They are nocturnal predators.	These are herbivores or carnivores.
Example spider, lice, mites	Example- crabs, lobster, crayfish

Note: The similarity between arachnids and crustaceans is they both are bilaterally symmetrical with a triploblastic body. They are haemocoelomic. The digestive system of these organisms is complete. They both are cold blooded animals.