A crustacean is an organism that belongs to the Kingdom Animalia, Phylum Arthropoda, and in the class Crustacea. Examples of the organisms belonging to this class are lobsters, woodlice, krill, shrimp, barnacles, crayfish, and crabs. There are over 67,000 species that belong to the Crustacean class. Crustaceans are different from other arthropods because of their limbs which are parted into two, their larval stages, and the modification of the appendages.
Characteristics and Structures
Crustaceans have three body parts, the head and thorax are fused to form a cephalothorax, and the abdomen. The cephalothorax is covered by a single carapace. Their bodies are usually segmented. Each segment has a pair of appendages. On the segment that forms the head, there are two pairs of appendages which form the antenna. These are the mandibles and the maxillae. The rest of the segments have appendages that are modified to perform functions like locomotion and feeding. The entire body of the crustaceans is covered by a hard exoskeleton, just like the other arthropods. The exoskeleton protects the body from predation and dehydration. To allow the body to grow, the exoskeleton is shed off at particular growth stages.
Most of the crustaceans reproduce sexually and have separate sexes. However, there are a few crustaceans that are hermaphrodites; they have both female and male reproductive parts on the same body. Examples of hermaphrodites crustaceans are barnacles, remipedes, and cephalocarids. In some instances, some crustaceans may change their sex during their lifetime. Parthenogenesis, a situation where a female organism lays fertilized eggs that hatches without the need of a male organism has been observed in some of the crustaceans. This occurs in many branchiopods. They either release the eggs to the water or hold onto the eggs until they are hatched. Some of them have sacs that hold the eggs until they are hatched.
Ecology and Habitat
Most crustaceans are aquatic organisms. Majority of them live in marine environment but a few live in freshwater. Some of the crustaceans are terrestrial. The terrestrial crustaceans include terrestrial crabs, terrestrial hermit crabs, and the woodlice. Most of the crustaceans are independent, they move around their habitat freely. However, there are a few that are dependent on their hosts. Most of these parasitic crustaceans are not adapted to rapidly respond to fluctuations in salinity. The bodies of their hosts protect them because the salinity of the body changes gradually compared to the salinity of the water. There are also a few species of the crustaceans that are sessile, such as the barnacles. Being sessile means that they cannot move on their own, they are attached to substrates such as rocks and corals.
Crustaceans as Food
Most crustaceans make delicious meals to human beings. The crustaceans that are consumed are mainly the decapods, literarily meaning ten-footed. The most common decapods consumed are crabs, prawns, lobsters, shrimp, and crawfish. Non-decapod crustaceans like krill are not so commonly consumed like the decapods but a meal in some parts of the world. Crustaceans are commonly consumed in Asian countries, with China as the country with the highest rate of crustaceans’ consumption.