Crabs belong to crustaceans in terms of category.From the point of view of living environment, they spend most of their time in the water.Many people are on land when they see crabs, so they think that they are animals living on land and can not breathe in water.In fact, crabs belong to aquatic animals, most of their life activities are carried out in the water.Crabs can stay in the water for a long time without drowning, because they breathe with gills, and they can breathe freely in the water, just like fish use gills to breathe.
However, from the specific structure and appearance, crab gills and fish gills are different.The gills of crabs are actually filaments from the outside, and the inside is composed of some very thin blood vessels.With this structure, crabs can breathe freely in the water.In fact, crabs not only do not drown in the water, but also can breathe on land for a period of time, because they can store part of the water to supply their breathing.
As mentioned above, crabs can breathe in the water, because their main respiratory organs are gills, which can breathe freely in the water.When water flows through their gills, oxygen in the water can enter their bodies through these blood vessels, and other water and substances will flow from both sides of their gills to the water beside them.This process will continue to cycle, and fresh water will continue to flow through their gills.
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