Arthropoda: Arthro-Jointed, Poda-Legs/Appendages

• Arthropoda is the largest group of animals.
• Habit and Habitat: they are free-living organisms found everywhere like on land, soil, water and some also lives as parasites on plants and animals.
• Symmetry: they are bilaterally symmetric [left and right side of the body has same design].
• Body cavity: body cavity is present which is filled with blood. So it is known as hemocoel.  True coelom is limited to some parts of body
• Body differentiation: They are multicellular, real developed organs are present.
• Germ layer: They are triploblastic animals.
• Body organization: They have segmented body but segmentation is less than that in annelid. Segments are divided into three regions- head, thorax and abdomen. They have jointed legs in three or more pairs.
• Skeleton:  Exoskeleton is made up of cuticle which is chemically composed of chitin.
• Life processes:

1. Alimentary canal/ digestive tract is complete and straight having two openings- mouth and anus.
2. Open blood circulatory system is present.
3. Respiration occurs through body surface, book lungs or by gills.
4. Excretion takes place through structures malphigian tubules.
5. They are unisexual. Reproduction is sexual with internal fertilisation.

Examples:

Scorpion, prawn, spider, housefly, mosquito, millipede, centipede, moth, honey bee etc.