Facts about Crabs
The telson is no longer functional in crabs, and the uropods are absent, possibly having evolved into small devices for holding the reduced abdomen tight against the sternum (Guinot and Bouchard 1998).
The gills of crabs are formed of flattened plates ("phyllobranchiate"), resembling those of shrimp, but of a different structure (Taylor and Taylor 1992).
An asterisk (*) marks the crabs included in the clade Thoracotremata.
Several other groups of animals are either called crabs or have the term "crab" in their names.
The mouthparts of crabs are covered by flattened maxillipeds, and the front of the carapace does not form a long rostrum (Dixon et al.
In all but a few crabs (for example, Raninoida), the abdomen is folded under the cephalothorax.
Anomuran "crabs" can be distinguished from true crabs by counting the legs.
The radiation of crabs in the Cretaceous and afterwards may be linked either to the breakup of Gondwana or to the concurrent radiation of bony fish, the main predators of crabs (Wдgele 1989).
The evolution of crabs is characterized by an increasing robustness of the body, and a reduction in the abdomen.
True crabs have five pairs of legs, the first of which is modified into a pair of claws and is not used for locomotion.
Crabs ingest food through their mouths just as we do, but do not use teeth to grind it. Depending on the species, they may have only soft, feathery mouthparts, or much harder ones. The hermit crab (Coenobita clypeatus) has delicate mouthparts called maxillopeds that help move food into its mouth.
Land hermit crabs are the species know as coenobito clypeatus. They have many stages in life. The female holds several hundred eggs inside her shell while they mature and later they hang out over the shell as they grow. The eggs are attached to her abdomen and appendages until they are ready to hatch.
They look a lot like crabs and many have the word 'crab' in their name, but are not true crabs. Anomurans can be told apart by the number of legs: crabs have ten legs, including claws, while the last pair of an anomuran's legs is hidden inside the shell, so that only eight legs are visible.
A blink of an eye, or a flick of an antenna, in the grand scale of things. The terrestrial track record of insects stretches as far back as 400 million years ago. Caribbean hermit crabs are also called soldier crabs.Jul 5, 2012
“The crab only needs to see one dark spot moving in its upward vision to know it must run for its burrow,” Jan says. ... The beach where they live is drenched in ultraviolet light, and the team has found that crabs can see in the near ultra-violet as well as other colours.Oct 26, 2009
“Call it color-coding your food,” said Johnsen. If the creatures can see green, blue and ultraviolet light, they might be capable of distinguishing between UV-emitting anemones and green-glowing toxic corals (which are not safe to eat) and blue-glowing plankton (which are the crabs' primary food source).Sep 7, 2012
Looking Around. One of the most ancient members of the crab family, horseshoe crabs have primitive eyes spaced around their body. Two median eyes on top of his shell monitor visible light, and an endoparietal eye is sensitive to UV waves.