Phylum Arthropoda

Arthropoda (Greek arthros, jointed; podes, feet) is the largest phylum in the entire animal kingdom, and contains its single largest class, Insecta, whose total species estimates range from 2 to 10 million. Arthropods are bilaterally symmetrical, segmented, triploblastic, schizocoelomate animals with organ-system organisation, and their defining feature — the one that names the phylum — is a set of jointed appendages used for locomotion, feeding, and sensing.

The body is covered by a chitinous exoskeleton that protects the animal and prevents water loss, and because this rigid covering cannot grow, it must be shed periodically in a process called moulting (ecdysis). The body is organised into a head, thorax and abdomen, with a body cavity called the haemocoel (part of an open circulatory system). Respiratory organs vary by habitat and group — gills, book gills, book lungs, or a tracheal system. Sensory organs are well developed, including antennae, simple and compound eyes, and statocysts (balance organs). Excretion is carried out through malpighian tubules, green glands or coxal glands depending on the group. …