Among the arthropods, crustaceans (literally those with a crust) the crab include more than 60,000 species of extremely varied forms.
It was a range from the tiny planktonic copepod, to the small amphipod hopping in dry algae on beaches, to the barnacle attached to rocks and the enormous lobster.
Crab Animated Images
They are overwhelmingly aquatic, breathe with gills and pass through an early developmental stage called the nauplius larval stage.
Practically all the large crustaceans and those we eat belong to the group of “decapod malacostracés that is to say 15,000 species, including our 7,000 crabs.
A single carapace or cephalothorax covers Their head and thorax. It includes the two cavities sheltering the gills.
Their head bears compound eyes, located at the end of a peduncle, antennae, and antennules with a sensory role and small appendages – mandibles, jaws, and maxillipedes – which chew and crush food.
They have five pairs of thoracic legs (or pereiopods), one to three of which end in claws.
In crabs, the cephalothorax is generally very enlarged, and the abdomen, which is reduced, is folded against it.
This vital structure allows it to walk, solidly supported on the substrate, and be very mobile in its movements. This evolutionary tendency, which, over the geological ages, has given crabs this conformation, is called carcinization.
Crabs are amphibious animals because they can live both in the open air and in water, sealing the gills.
Their diet includes fresh algae, small echinoderms, actinias, organic debris, insect larvae, worms, small fish trapped in nets, and do not disdain organic matter of various types in an advanced state of decomposition.
The specimens that prefer the mainland to populate the tropics area are mainly omnivorous and return to the water only to mate. Some species modify the shell twice a year, during the seasonal change.
During the mating phase, the female changes her shell shortly after the male becomes softer and favors fertilization.
The females carry their eggs under the tail, and at hatching, they die, the larvae get accepted by the current, and after nine months, they measure only three millimeters.
After a few years, they reach twenty-five millimeters, but sexual maturity is reached only around five years of age.
They are brilliant and careful animals that are difficult to find and identify because they love to blend in groups or hide.
They lead almost nightlife, which protects them from the most dangerous predators’ presence and camouflages them from sight.
Sometimes they cover the carapace with other organisms such as sponges, marine vegetables, small crustaceans to camouflage and conform to the environment and the seabed.
They are excellent walkers and can cover in a day even twelve kilometers, a path that they do both to reach the place to reproduce and that will be retraced in reverse by the young once born.