🌟 Important Words & Concepts Explained
Here are the important terms and concepts from the lesson on Phylum Mollusca and Phylum Annelida, explained in simple and detailed language to help students understand the foundation of the lecture:
🔑 Key Terms & Concepts:
1. Mollusca
A large phylum of soft-bodied animals, usually with a hard shell. They live in water or moist environments. Examples include snails, oysters, and octopuses.
2. Triploblastic
Organisms whose bodies develop from three embryonic layers:
- Ectoderm (outer layer)
- Mesoderm (middle layer)
- Endoderm (inner layer)
This allows for more complex body structures.
3. Bilateral Symmetry
The body can be divided into two equal left and right halves. It shows a front and back, left and right, and top and bottom.
4. Coelom & Coelomate
A coelom is a fluid-filled cavity inside the body that contains internal organs.
Animals with a coelom are called coelomates. It gives space for organ development and cushioning.
5. Protostome
A group of animals in which the mouth develops first during embryonic development. Molluscs and annelids are protostomes.
6. Mantle & Mantle Cavity
- Mantle: A body layer in molluscs that covers the internal organs.
- Mantle cavity: The space between the mantle and the internal body, where gills and excretory organs are located.
7. Shell
In many molluscs, the mantle secretes a shell made of calcium carbonate to protect the body.
8. Radula
A rasping tongue-like organ in molluscs (except bivalves), used to scrape food from surfaces.
9. Open Circulatory System
Blood does not stay inside vessels but flows through body cavities, bathing organs directly. Most molluscs have this system.
10. Nephridia
Tubular structures that remove waste from the body. Like a primitive kidney.
11. Gills
Used by molluscs for gas exchange — taking in oxygen and releasing carbon dioxide.
12. Ganglia
Masses of nerve cells (like simple brains). Molluscs and annelids have ganglia in different body parts for controlling body functions.
13. Foot (in molluscs)
A muscular structure used for movement, digging, or attachment to surfaces.
14. Annelida
A phylum of segmented worms. These animals have their bodies divided into rings or segments. Examples include earthworms, leeches, and nereis.
15. Metamerism / Segmentation
The body is divided into repeating segments. Each segment has organs and systems, which helps in movement and survival.
16. Setae
Chitinous bristles found on each segment (except in leeches), which help in movement.
17. Cuticle
A moist outer covering of the body that protects and allows for gas exchange in annelids.
18. Closed Circulatory System
Blood stays within blood vessels and is pumped by hearts or vessels. More efficient than open systems. Found in annelids.
19. Pseudohearts
Specialized blood vessels in annelids that contract rhythmically to push blood — act like hearts.
20. Respiration through Skin
Annelids (like earthworms) exchange gases through moist skin, instead of lungs or gills.
21. Photoreceptors
Light-sensitive organs that help some annelids detect light and darkness.
22. Hermaphrodite
An animal that has both male and female reproductive organs. Most annelids, like earthworms, are hermaphrodites.
23. Unisexual
Male and female organs are in separate individuals. Most molluscs and some annelids are unisexual.