Spider crab

Spider crab refers to the various species of crabs of the family Madijae. They fall under the class Crustacea. The family Madijae consists of 700 marine species of crabs. Dorsal section of their exoskeleton is greater in length than in breadth. Their exoskeleton is bristled. In some species of this family, the legs are long. This characteristic became the reason for the name spider crab.

Most of the spider crabs have thick and rounded booties. They are sluggish animals. Mostly spider crabs are scavengers of dead flesh. Dead starfish and mollusks are a part of their diet. They are found in the Atlantic as well as the Pacific regions and many nightmares. Many spider crabs inhabit rocky substrata while some prefer muddy regions. Their sizes range from 12 mm to 4 m. Their shell and their legs are covered with setae. A Spider crab is dimorphic. After mating, the female stores sperm in her spermatheca. One mating suffices several subsequent fertilizations.

Maja squinado is also known as the European spider crab. It is mainly found in regions where the seabed is soft and has soft substrata. These crabs are found partially buried in the substrata. Adult males may be found in regions where the seabed is rocky. The European spider crab lives for around 5–8 years and undergoes the larval stage followed by the juvenile stage before it becomes an adult. Adults maintain an omnivorous diet and adapt to eating a wide range of food available in the regions of their inhabitance. Marine algae form a major part of their diet. A unique feature of Maja squinado is that it can copulate even when the female is hard whereas other species of its phylum require the female to exuviate before mating. These spider crabs occur in the northeastern regions of the Atlantic and in the Mediterranean Sea. A striking feature of the European spider crabs is that they seasonally migrate. They migrate in autumn, sometimes covering 100 miles in 8 months.

The Japanese spider crab, also known as the Macrocheira kaempferi, is the largest living arthropod. Its body size is of about 37 cm and it can weigh up to 20 kilograms. It can live for about 100 years, an amazingly long lifespan. It is named after Engelbert Kaempfer, the German traveler and naturalist. It has an orange body and white spots on its legs. It has compound eyes on the anterior side with two thorns jutting from between them. Japanese spider crabs are found in the Pacific region in Japan. They commonly live as deep as 150–800 meters in the seabed. They lay eggs during the spring season. Japanese spider crabs are eaten and used for ornamental purposes. They are also used for research purposes. Today, a decrease in the population of these crabs is observed and efforts are being taken to protect them.

Portly spider crabs are found in the estuarial regions on the eastern coast of North America. The Portly spider crab is called Libinia emarginata. It has a spiny back; its carapace is shiny and hairy. It is brown or yellow colored with white claws. The hair on its carapace serve as its means of camouflage. It does not harm the human beings. As most other spider crabs, it is a slow mover and a scavenger.

The Hyas genus of spider crabs consists of the famous Great Spider Crab. The Great Spider Crab is called Hyas araneus. The Hyas araneus is reddish brown in color and has a pear shaped carapace. The extension of its carapace that projects between its eyes splits into two parts. Hyas spider crabs are found in the Atlantic regions and in the North Sea.