Arthropod

NOTE: Some classification schemes group Myriapoda and Hexapoda into one subphylum called Uniramia.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Arthropods (Phylum Arthropoda) are the largest phylum of animals and include the insects, arachnids, crustaceans, and other similar creatures. In approximate statistics, over eighty percent extant (living today) animal species are arthropods, with over a million modern species described and a fossil record reaching back to the early Cambrian. Arthropods are common throughout marine, freshwater, terrestrial, and even aerial environments, as well as including various symbiotic and parasitic forms. They range in size from microscopic plankton (~0.25 mm) up to forms several metres long.

Related Topics:
Phylum - Animal - Insect - Arachnid - Crustacean - Cambrian - Mm

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

The Arthropoda make up a very successful phylum? 75% of all animals on Earth are arthropods. The Greek word Arthropoda means "jointed feet."

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

The arthropods have a segmented body with appendages on each segment. They have a dorsal heart and a nervous system on the ventral side of their bodies. All arthropods are covered by a hard exoskeleton that is made out of chitin, a polysaccharide. Periodically, an arthropod sheds this covering when it molts. This covering prevents the arthropod from drying out, but also prevents arthropods from growing too big. The arthropod group identified with the subphylum Chelicerata is the class Arachnida. The most familiar arachnid is the spider. These organisms have two body regions, ten jointed appendages, simple eyes, and often carry on respiration by means of book lungs. Their chelicerae are hollow fangs that pierce prey. The second appendages, the pedipalps, contain sensory receptors. They also have four pairs of jointed legs. On the tip of the abdomen of many spiders there are spinnerets, which they use to make silk for their web. Other arachnids include the scorpions, with their pedipalps shaped like pincers, and the mites and ticks, which can be destructive to both plants and animals.

Related Topics:
Dorsal - Ventral - Exoskeleton - Chitin - Chelicerata - Arachnida - Spider - Eyes - Book lungs - Fangs - Pedipalps - Legs - Abdomen - Spinnerets - Silk - Scorpion

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Lobsters, crabs, shrimp, and barnacles belong to the class Crustacea. Their bodies are divided into three parts: abdomen, thorax, and head. Most are aquatic and use gills for respiration. The young stage is a nauplius larva. The number and type of head appendages helps to determine the crustaceans. One typical crustacean which looks like a lobster is a crayfish. It has four pairs of antennae on its head. Large eyes are attached on the head. Behind those are its mandibles or jaws, which are used to chew food. They are helped by the two pairs of maxillae right behind them. The crayfish also has walking legs and claws on its thorax region. On the abdomen are appendages called swimmerets that females use to hold their eggs. Other groups of arthropods include the Diplopoda, commonly known as millipedes, and the Chilopoda, or the centipedes. A major difference between these groups is the number of legs on each segment.

Related Topics:
Lobsters - Crabs - Shrimp - Barnacles - Crustacea - Aquatic - Gills - Crayfish - Antennae - Mandibles - Jaws - Maxillae - Millipedes - Centipedes

~ ~ ~ ~ ~ ~ ~ ~ ~ ~