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Arthropoda

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Arthropoda

Arthropods are animals belonging to the phylum Arthropoda, which is the largest of all phyla in the Animal Kingdom, with more than one million species, making them almost 80% of the whole kingdom. These include insects, arachnids, crustaceans and many more, most of which are quite small, the biggest being the Japanese Spider Crab with a leg span of 3.5 meters and the smallest being the microscopic Plankton.

*Characteristics:

- Segmented Body.

- Exoskeleton. This is a hard outer body covering which protects the internal organs.

- Jointed legs. The name ‘arthropod’ comes from Latin, meaning ‘joints’.

- Specialized mouth parts.

- Compound eyes.

- Nervous system consisting of a brain.

- Sexes mostly separate.

- An open circulatory system.

*Classification:

Subphyla:

Arachnida is a subphylum of Arthropoda, consisting of over 100 000 species, many of them being parasites which can carry disease. They are found in all environments, and mostly have eight legs, which is a feature, together with the fact that they do not have wings or antennae, often used to distinguish them from the other subphyla, though there are exceptions. They include spiders, scorpions, ticks and mites. Their bodies are divided up into three parts: the cephalothorax, the opisthosoma and the thorax, and use a type of lung for gas exchange. Most Arachnids are carnivorous, and eat pre-digested insects and other small animals. They reproduce using internal reproduction usually lay eggs, except for the scorpion which bears living young. The word ‘Arachnid’ comes from the Greek word ‘Arachne’ meaning ‘spider’.

Crustacea is a large subphylum of Arthropoda, consisting of almost 52 000 described species, including animals like crabs, lobsters, shrimp and barnacles. The majority of these are aquatic, living in marine or fresh water environments, though some have adapted to living on land like some crabs and woodlice. Most crustaceans are relatively small, though there are some exceptions. All of them have a hard, strong exoskeleton, divided into two parts, which has to be shed in order to allow the animal itself to grow. They have a large circulation system, where blood is pumped around the body by the heart. Only some crustaceans have sexes separate, and those that are usually mate seasonally and lay eggs. The study of Crustacea is called carcinology.

Diplopoda is a class, belonging to the subphylum of Arthropoda Myriapoda, consisting of about 10 000 species of animals which have two pairs of legs for each body segment and are often known as Millipedes. Hence the name, they do not have one thousand legs.
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