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Crustaceans are components of the Crustacea class, which derives from the fact that many species in this group have an exoskeleton enriched with calcium carbonate, forming a crust. This is what happens in lobsters, shrimps, crabs and crabs, the best known representatives of the group.
In addition to the exoskeleton the crustaceans have articulated appendages and a segmented body. In crustaceans, the head and chest are fused into one piece, the cephalothorax; On the head there are two pairs of antennas and the abdomen has birrem swimming articulated appendages (two branches attached to a base). In the head are present, in addition to the two pairs of antennas, two compound eyes, usually pedunculated, and around the mouth, a pair of jaws and other accessory appendages in obtaining the food.
Crustacean Respiratory System
Crustaceans are animals adapted to life in the aquatic environment, breathing through gills that usually develop at the base of the thoracic appendages.
Most crustaceans live in the marine environment, although there are many representatives of freshwater. These range from microscopic forms that abound in plankton, to larger forms, adapted for swimming, to walk on the bottom, and even sessile forms, whose adults live fixed on the rocks. In addition to the free life forms, there are crustaceans that parasitize other animals.
Although the majority of crustaceans are aquatic, there are species that have invaded the terrestrial environment, such as the garden armadillo (or armadillo), the beach cockroach (genus Ligia) and terrestrial or ghost crab ( genus Ocypode), very common in the dry parts of our beaches and sand dunes.
These forms, however, do not have complete adaptations to the terrestrial environment, depending on their breathing gills, which must always be moistened or kept moist for gas exchange.
Crustacean excretory system
Crustaceans are excreted through a pair of green glands or antennae, located near the antennae and opening outwards through an excretory pore at the ventral base of the second antennae.
Most crustaceans are of separate sexes, although there are hermaphrodite species, fertilization is crossed, involving copulation. Crustacean females generally incubate their eggs in body appendages, as with lobsters and crabs, or in ovigerous sacs formed when eggs are expelled, as in copepods. In most cases, development is indirect, with free-living larvae, and there may be more than one type of larva in the same life cycle. Usually, from the egg comes a nauplian larva, which turns into a zoez larva, but this pattern varies greatly from group to group.
In some species, such as crayfish, larval stages are suppressed, and from the egg emerges a young: development in these cases is direct.