Why are crabs not insects?

The reason why crabs are not insects

Crabs and insects are both arthropods. Crabs belong to the crustaceans in the arthropod phylum. Insects are arthropods among invertebrates.

The characteristics of crabs:

(1) Crustaceans of the Arthropod phylum, whose body is protected by a hard shell, breathe by gills.

(2) Compound eyes (consisting of many lenses) sometimes grow on elongated supports. Stretching out from the head are two pairs of knotted tentacles (tentacles), which usually act as sensory organs and sometimes as swimming organs. Usually the two outer tentacles are much longer than the inner pair.

(3) The general appendages of the arms on the chest usually have a pair of large pliers. These appendages are used for walking, grasping, tearing and eating. The appendages on the tail are used for swimming.

(4) Most types of crabs live in the sea or offshore areas, and some live in freshwater or land. They rely on female crabs to give birth to small crabs. Each time the female crabs lay a lot of eggs, the number can reach millions of pieces.

Insects generally have the following characteristics:

(1) The body is clearly divided into three parts: head, chest and abdomen, and each part is composed of several links. The head is formed by the healing of 6 links, and the adult body has no joint marks. The chest consists of three sections: the front chest, the middle chest and the back chest. The abdomen is composed of 3-12 segments, most of which are 10-11 segments.

(2) The adult has three pairs of segmented feet, which grow on the three thoracic segments. (Animals with less than three pairs or more than three pairs of legs are not insects. This is the most obvious sign for identifying insects.)

(3) Most insects have two pairs of wings on the breasts of adults. Some types of insects have evolved to only one pair of wings (such as mosquitoes and flies), and some types of insects have completely degraded wings (such as fleas and lice). .

(4) A pair of segmented antennae grow on the head of an insect, which has the function of touch and smell, and is used to find the way, find food, distinguish the direction and courtship.

(5) There is no bone in the insect body, and there is a shell on the surface of the adult insect, which is called “exoskeleton”

Overview of crab species

Crabs, known academically as Brachyura, is a class of Decapoda. Because the classification of Arthropods is still controversial, it is sometimes regarded as a suborder. Short-tailed animals are generally called crabs or crabs in Chinese colloquially. Most animals in this category live in the sea, but many live in fresh water or on land. The lower abdomen of brachyura is actually deformed from a very short tail carapace. In long-tailed animals (such as shrimp) this tail is directly attached to the back of their tail, and in brachyura, it is on the abdomen breastplate. the following. Their first pair of feet becomes a pair of very large forceps (some types of forceps are not symmetrical), and their eyes are on a pair of rods.

The largest crab on the planet is the spider crab. Their feet are 3.7 meters wide. The smallest crab is the bean crab, which is less than half a centimeter in diameter.

Crabs are omnivorous animals. They mainly live on seaweed, but sometimes they also eat microorganisms, insects, etc.

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