The word athropoda is derived from the Greek word arthron meaning 'joint' and pous meaning foot. Arthrods are invertebrate animals that possess an exoskeleton, a segmented body and paired jointed appendages.
General Characteristics of Arthropods
- Arthropods are successful in almost all habitats on earth.
- Ancient arthropods were the first animals to live most of their lives in terrestrial environments.
- Metamerism with stigmatization, a chitinuos exoskeleton and metamorphosis has contributed to the success of arthropods.
- About one million species has been discovered but study have it that the undescribed species are more than the described ones.
- Arthropods are considered the most successful in all animals.
- Their metamerism is modified by the specialization of body regions for specifically functions(tagmatization).
- Their chitinous exoskeleton provides support and protection. It is therefore modified to perform sensory functions.
- They have paired jointed appendages.
- They grow through a process called ecdysis or moulting.
- They have a ventral nervous system.
- Their coelom is reduced to cavities surrounding gonads and sometimes excretory organs.
- They have open circulatory system in which blood is released into tissue space derived from embryonic blastocoel.
- They have a complete digestive tract.
- Competition between immature and larva stage is reduced due to metamorphosis.
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THE CUTICLE
Cuticle is a non-cellular supporting hard chitinous multilayered exoskeleton. It is secreted by hypodermis. It covers the entire body surface and extend inward to line the fore gut, hind gut as well as the trachea in insect. In addition, projection of the cuticle provides point for muscle attachment.
The adaptability of the cuticle has made possible the many the modification of arthropods to fill many different ecological niches.
- The cuticle is fashioned into mouth parts variously modified for different modes of feeding and diet.
- The rigid structure of the cuticle provides support for the body.
- The problem of water loss is reduced in arthropod due to high impermeability of the cuticle.