Gr. Arthos : Jointed podos: legs
- Animals with jointed legs
- Largest phylum in Animal kingdom in both number of taxa and biomass
- Most successful group of animals due to chitinous skeleton.
- Bilaterally symmetrical, triploblastic, metamerically segmented and tagmatization
- Segments are not separated as in annelids; external segmentation is present.
- Organ system level of body organization.
- Body is divided into three tagmata : head , thorax and abdomen ; Head and thorax are fused in some animals called cephalothorax
- Reduced coelom in adult ; body cavity consists of haemocoel ; so called haemocoelomate.
- Alimentary canal completing consisting of foregut, midgut and hindgut.
- Mouthparts adapted for various modes of feeding :
Biting and chewing type : Cockroach , grasshopper etc.
Chewing and lapping : Bees and wasps
Piercing and sucking : Bugs, Aphids, Mosquitoes
Sponging : Housefly
Siphoning : Butterflies and moths
- Circulatory system open type with dorsal contractile heart.
- Respiration by general body surface or special structure such as gills, trachea or book lungs.
- Excretory system are coxal glands, green or maxillary (in aquatic forms) and Malpighian tubules (in terrestrial forms).
- Major excretory product is uric acid
- Nervous system with dorsal nerve ring and a double ventral nerve cord.
- Sense organs comprise antennae, simple eyes, compound eyes, statocysts, chemoreceptors and taste receptors.
- Usually dioecious. Fertilization internal.
- Majority are oviparous, few like scorpios are ovoviviparous.
- Development direct or indirect, one to many larval stages, parthenogenesis in some.
CLASSIFICATION
Subphylum 1 : ONYCHOPHORA
Most primitive ; commonly called velvet worms or walking worms
eg : Peripatus (connecting link of arthropods and annelids)
Subphylum 2 : TRILOBITOMORPHA
These are fossil arthropods
Subphylum 3 : CHELICERATA
1st pair of appendages are chelicerae , second pair are pedipalps.
Body divided into prosoma (cephalothorax) and opisthosoma (abdomen)
Subphylum 4: MANDIBULATA
Body divided into head, thorax and abdomen, have one or 2 pairs of antennae, a pair of jawa (mandibles), one or two pairs of maxillae
