Insects, spiders, crustaceans, and other invertebrates are all members of the phylum Arthropoda. Arthropods are the most numerous creatures on Earth, with over a million identified species. They are important pollinators, decomposers, and prey for other creatures in ecosystems. Arthropods have a strong exoskeleton and segmented body, allowing them to adapt to a variety of settings. Understanding the biology and behavior of arthropods is critical for pest species management, drug development, and ecological study.
Characteristics of Arthropoda
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 of Arthropoda
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