Phylum Arthropoda – The Most Diverse Invertebrates

 

📘 Phylum Arthropoda – The Most Diverse Invertebrates

🔹 General Characteristics:

• Includes insects, crustaceans, spiders, scorpions, centipedes, etc.
• Found in all types of habitats – terrestrial, aquatic, aerial.
• Many terrestrial species (especially insects) have the ability to fly.

🔹 Body Structure:

• Triploblastic, bilaterally symmetrical, protostome coelomates.
• Reduced coelom, found mainly around reproductive and excretory organs.
• Have jointed appendages specialized for:
• Running, crawling, swimming, capturing prey, reproduction, respiration, etc.

🔹 Exoskeleton & Growth:

• Covered by a chitinous exoskeleton (cuticle), secreted by the epidermis.
• Exoskeleton is periodically shed and replaced to allow growth.
• This process is called ecdysis or molting.

🔹 Circulatory System:

• Open-type circulatory system.
• Blood flows through body cavity called hemocoel (from blastocoel).
• Blood is colorless and called haemolymph (no hemoglobin).

🔹 Respiratory System:

• Tracheal system (in terrestrial forms):
• Air enters via spiracles, flows through trachea.
• Gills (in aquatic arthropods like crabs, shrimps, prawns).

🔹 Digestive & Excretory System:

• Complete, tube-like alimentary canal with divided regions.
• Excretion via Malpighian tubules:
• Remove uric acid (in solid form), open into midgut–hindgut junction.

🔹 Nervous System & Sense Organs:

• Well-developed CNS with:
• Fused cerebral ganglia (brain) in head.
• Double ventral nerve cord with ganglia in each segment.
• Possess compound eyes and antennae for sensing the environment.

🔹 Reproduction:

• Unisexual (separate sexes).
• High reproductive potential contributes to their evolutionary success.

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✅ Key Point:

Arthropods are the most successful invertebrates, with over 900,000 named species, accounting for two-thirds of all known species on Earth.

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🔹 Important Examples:

✅ Insects:

• Mosquito, Butterfly, Moth, Wasp, Beetles, Grasshopper

✅ Crustaceans:

• Crab, Lobster, Prawn, Shrimp, Crayfish

✅ Arachnids:

• Spider, Tick, Mite, Scorpion

✅ Myriapods:

• Centipede, Millipede

Related Topics

• Phylum Nematoda
• Phylum Molluska
• Phylum Annelida