Chelicerata is a large and diverse group of invertebrate animals. It includes insects, spiders, and a host of other arthropods. They are found on land and in water. There are seventy-seven thousand species. The earliest known chelicerate fossil dates back to 508 million years ago.
Chelicerates are predatory arthropods that use their clawed appendages to grasp and shred their food. They also suck liquid food from their prey. In addition, chelicerates can secrete digestive enzymes into their prey.
Although most chelicerates are predators, some are carnivorous and some are detritivorous. Crustaceans are divided into two groups: eurypterida and pycnogonida. Eurypterida first appeared in freshwater deposits from the Silurian period. Pycnogonida are sometimes included in the chelicerate taxon, but they are often excluded.
Chelicerates have two body parts, the prosoma and the opisthosoma. The prosoma is formed from eight segments. Each segment is articulated and separated by articular membranes. Most chelicerates have pedipalps. Pedipalps are located next to the prosoma. These appendages may be modified for a variety of functions.
The nervous system of chelicerates is composed of a brain, two ventral nerve cords, and two tracheae. In some species, the ganglia of living chelicerates fuse into large masses in the cephalothorax.
Chelicerata is a member of the largest phylum of animal life. Many of its closest fossil relatives are trilobites, a class of marine arthropods. Trilobites also have jointed limbs, a tough cuticle, and a protective exoskeleton.
Chelicerata includes spiders, scorpions, horseshoe crabs, and many more. They are most common in soil and fresh water, but some live in open oceans.