Mollusca - Kingdom: Animalia - SS1 Biology Lesson Note

Mollusca is a phylum of soft-bodied invertebrate animals that includes diverse organisms such as snails, clams, squids, and octopuses. Mollusks are found in various habitats, including marine, freshwater, and terrestrial environments.

 

Figure 32 Images from istockphoto.com

Figure 33 Images from stockadobe.com

 

Here are some key features and characteristics of Mollusca:

1. Body Structure: Mollusks have a soft, unsegmented body that is typically covered by a hard shell made of calcium carbonate. The body consists of three main parts: the head, foot, and visceral mass. The head contains sensory organs and feeding structures, while the foot is used for locomotion. The visceral mass houses the internal organs.

2. Mantle and Shell: Mollusks possess a mantle, a specialized fold of tissue that covers the visceral mass and secretes the shell. The shell provides protection and support for the animal. However, not all mollusks have a shell; some species, like slugs and octopuses, lack shells entirely.

3. Radula: Most mollusks have a unique feeding structure called a radula, which is a specialized organ covered in rows of tiny teeth. The radula is used for scraping, cutting, or drilling food sources, depending on the diet of the species.

4. Reproduction: Mollusks exhibit various reproductive strategies. Most species are dioecious, meaning they have separate sexes (male and female). Fertilization can be external or internal, and some mollusks undergo complex courtship rituals. Some mollusks also can reproduce asexually through processes such as fragmentation or budding.

5. Ecological Importance: Mollusks play essential roles in ecosystems. They contribute to nutrient cycling, serve as prey for various organisms, and some mollusks act as filter feeders, helping to maintain water quality. Mollusks also have economic significance as a food source and in industries such as pearls and shellcraft.