🌟 Important Words & Concepts Explained

🕷️ Phylum Arthropoda – Key Terms and Concepts

1. Arthropods

  • Animals with jointed legs and a hard external skeleton (exoskeleton).
  • Examples: Insects (ants), crustaceans (crabs), arachnids (spiders), and centipedes.

2. Triploblastic

  • Their body develops from three embryonic layers: ectoderm, mesoderm, and endoderm.
  • This gives rise to complex tissues and organs.

3. Bilateral Symmetry

  • The body can be divided into two equal left and right halves along a single plane.

4. Protostome Coelomates

  • They develop a true body cavity (coelom) from the mesoderm.
  • In protostomes, the mouth forms before the anus during embryonic development.

5. Segmented Body

  • The body is divided into repeated units, some of which form special regions:
    • Tagmata: fused segments like head, thorax, and abdomen.

6. Jointed Appendages

  • Limbs are jointed like a robot arm and adapted for walking, feeding, swimming, etc.

7. Exoskeleton

  • A tough outer covering made of chitin that protects the body and prevents drying out.

8. Ecdysis (Molting)

  • The process of shedding the old exoskeleton so the animal can grow.
  • After molting, a new exoskeleton is formed.

9. Open Circulatory System

  • Blood (called haemolymph) flows through open spaces (hemocoel) instead of closed vessels.

10. Haemolymph

  • A colorless blood-like fluid without hemoglobin that flows in arthropods.

11. Tracheal System

  • Air tubes (tracheae) that carry oxygen directly to body tissues.
  • Air enters through spiracles, tiny holes in the body.

12. Malpighian Tubules

  • Part of the excretory system, removing nitrogenous waste like uric acid from the blood.

13. Compound Eyes

  • Eyes made of many small units (ommatidia), allowing a wide field of view.

14. Unisexual

  • Males and females are separate individuals.

⭐ Phylum Echinodermata – Key Terms and Concepts

1. Echinoderms

  • Marine animals with spiny skin and a unique body plan.
  • Examples: Starfish, sea urchins, sea cucumbers.

2. Radial Symmetry (Adults)

  • Body parts are arranged in a circular pattern, like spokes on a wheel.

3. Bilateral Symmetry (Larvae)

  • Larvae are bilaterally symmetrical, meaning they have a clear left and right side.

4. Deuterostomes

  • During development, the anus forms before the mouth.
  • This is opposite of protostomes like arthropods.

5. Endoskeleton

  • Internal skeleton made of calcium plates (ossicles) under the skin.
  • Often supports spines or bumps on the body.

6. Water Vascular System

  • A network of water-filled tubes that helps in movement, gas exchange, and feeding.

7. Madreporite

  • A sieve-like plate where water enters the water vascular system.

8. Tube Feet

  • Small, flexible extensions used for movement, gripping surfaces, and feeding.

9. Nerve Ring and Radial Nerves

  • Echinoderms don’t have a brain. Instead, they have a nerve ring around the mouth and radial nerves running through the arms.

10. Regeneration

  • Many echinoderms can regrow lost parts, and some can reproduce asexually by splitting and regenerating.

11. Unisexual

  • Male and female are separate organisms, unlike hermaphrodites.
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