Mollusca:
Mollusca, commonly known as mollusks, is a diverse phylum of invertebrate animals that includes a wide range of organisms such as snails, clams, octopuses, and squids. They are found in marine, freshwater, and terrestrial habitats around the world. Mollusca is the second-largest phylum in the animal kingdom, comprising over 60,000 recognized species.
Characteristics of Mollusca:
1. Soft-bodied: Mollusks have soft, unsegmented bodies that are often protected by a hard outer shell. However, some mollusks, like slugs and octopuses, have reduced or absent shells.
2. Bilaterally symmetrical: They exhibit bilateral symmetry, meaning their bodies can be divided into two similar halves along a central axis.
3. Mantle: Mollusks have a specialized tissue called the mantle, which secretes the shell in shell-bearing species and plays a role in respiration and locomotion.
4. Foot: Most mollusks possess a muscular foot, which is used for locomotion, attachment, or burrowing.
5. Radula: Many mollusks have a rasping tongue-like structure called a radula, used for scraping or tearing food particles.
6. Open circulatory system: Mollusks have an open circulatory system, with a heart that pumps hemolymph (a fluid similar to blood) into the body cavity.
7. Nervous system: They possess a simple nervous system, with ganglia and nerve cords, but some cephalopods (e.g., octopuses) have highly developed nervous systems.
Classification of Mollusca:
Mollusca is divided into several major classes, each exhibiting unique characteristics. Some of the significant classes include:
1. Gastropoda: This class includes snails and slugs. They typically have a coiled shell, a muscular foot for locomotion, and a head with sensory tentacles.
2. Bivalvia: Bivalves comprise clams, mussels, oysters, and scallops. They possess a two-part hinged shell and use their specialized gills for filter feeding.
3. Cephalopoda: This class consists of highly intelligent marine animals such as squids, octopuses, and cuttlefish. They have a well-developed head, large eyes, and tentacles with suckers.
4. Polyplacophora: Commonly known as chitons, these mollusks have a shell composed of eight overlapping plates and a muscular foot for locomotion.
5. Scaphopoda: Scaphopods, also called tusk shells, are a small class of mollusks with tubular shells open at both ends. They are usually found buried in the sediment.
| Class | Examples |
|---|---|
| Gastropoda | Snails, slugs, conchs, nudibranchs |
| Bivalvia | Clams, mussels, oysters, scallops |
| Cephalopoda | Squids, octopuses, cuttlefish, nautiluses |
| Polyplacophora | Chitons |
| Scaphopoda | Tusk shells |
| Monoplacophora | Neopilina |
| Solenogastres | Solenogasters |
| Caudofoveata | Chaetodermomorpha |
| Aplacophora | Worm-like mollusks |
These are just a few examples of the diverse classes within the phylum Mollusca. Each class further contains numerous species with their own unique adaptations and characteristics.
FAQ
Q: What is Mollusca?
Mollusca is a diverse phylum of invertebrate animals that includes creatures such as snails, slugs, clams, squids, and octopuses.
Q: What are the characteristics of Mollusca?
Characteristics of Mollusca include:
- Bilaterally symmetrical body
- Soft body often enclosed in a hard shell (although some species lack shells)
- Mantle, a fold of tissue that secretes the shell in shelled species
- Radula, a unique feeding organ found in most species
- Presence of a muscular foot or tentacles
- Open circulatory system
- Well-developed nervous system
Q: What are the classes of Mollusca and examples of each?
Mollusca is divided into several classes. Here are a few along with examples:
- Class Gastropoda: Examples include snails (e.g., garden snail - Helix aspersa) and slugs (e.g., banana slug - Ariolimax dolichophallus).
- Class Bivalvia: Examples include clams (e.g., quahog - Mercenaria mercenaria) and mussels (e.g., blue mussel - Mytilus edulis).
- Class Cephalopoda: Examples include squids (e.g., common squid - Loligo vulgaris) and octopuses (e.g., common octopus - Octopus vulgaris).
- Class Polyplacophora: Example includes chitons (e.g., giant Pacific chiton - Cryptochiton stelleri).
- Class Scaphopoda: Example includes tusk shells (e.g., dentalium shell - Dentalium elephantinum).
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