Like many crabs, they exhibit sexually dimorphic. They are relatively small sized crabs at about 3 cm wide even for the largest individuals. The fiddler crab builds burrows which they use to take refuge from predators, as well as to reproduce and hibernate during winters. The fiddler crab ( Uca pugnax) inhabits many marshes along the coastal areas of the Atlantic Ocean. From these eggs emerge larvae which will undergo different stages of metamorphosis until they reach adulthood. In relation to crab reproduction, they are oviparous animals, meaning they reproduce through eggs. Their hearts can be of variable shapes and contain very small holes (ostiles) which allow blood to travel in and out of it.Ĭrabs are omnivorous animals which feed on algae, fish, mollusks, carrion, bacteria and many other organisms. This means that blood sometimes travels through veins and arteries, but is poured into the body at other times. Crabs have an exoskeleton and their circulatory system is open. This water goes into the branchial chamber, takes in the oxygen and the pushes it back out through an area close to the eye. The water enters through the base of their first pair of appendages which circulate the water into the gills. A few species, such as the blue crab, have an adapted pair of back legs which act similarly to a paddle and allow them to move through the water.Ĭrabs which do live underwater breathe through gills. They may scuttle across the ocean floor instead. Even among those which dwell in water, crabs generally cannot swim. Some will move forward, or only move sideways when moving at speed. For example, males will often have larger claws.Ĭrabs are known for walking sideways, but not all crabs will move in this direction. Crabs are generally sexually dimorphic, meaning they differ in morphology depending on whether they are male or female. These claws are of various size and are used mainly for feeding, but also for fighting and securing a mate (the latter only in some crab species). Perhaps the most obvious difference in crabs is the fact they have claws. These are adapted arms which help the crab push food into its mouthparts and also to cut it into smaller pieces for easier ingestion. They have five pairs of legs as well as other appendages.

This gives them a generally quite flattened appearance. The carapace (upper section of their exoskeleton) of crabs is very broad, often wider than it is long.

The abdomen is also comparatively small and located on the underneath of their shell. Crabs, however, have these three body parts fused together. Most arthropods have a body which is divided into a head, thorax and abdomen. In general, they body structure is very specialized. Crabs are crustaceans, a type of arthropod which are differentiated by various factors, including the fact they have bi-parted limbs.

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