Characteristics of Shellfish:
Shellfish are a diverse group of aquatic invertebrates that share the common feature of having a hard, external shell for protection. Here are some key characteristics:
1. Shell:
* Hard, external exoskeleton: Composed of calcium carbonate, providing protection against predators and environmental stresses.
* Shape and structure vary: From the smooth, symmetrical shells of clams to the spiral shells of snails.
* May be single or multiple shells: Bivalves (clams, mussels, oysters) have two shells that hinge together, while univalves (snails, limpets) have a single, coiled shell.
2. Habitat:
* Marine, freshwater, or brackish water: Found in diverse environments, from shallow coastal waters to deep ocean trenches.
* Often benthic: Living on or in the bottom sediment, but some species may be free-swimming or attached to structures.
3. Feeding:
* Filter feeders: Most shellfish filter microscopic food particles from the water column, using gills or specialized structures.
* Herbivores: Some graze on algae or plants.
* Scavengers: Some feed on dead organisms or debris.
4. Reproduction:
* Mostly oviparous: Laying eggs that hatch into larvae.
* Larval stage: Free-swimming larvae, often planktonic, before settling and developing into adults.
* External or internal fertilization: Depending on the species.
5. Other Characteristics:
* Soft-bodied: The body is protected by the shell, lacking internal skeletons.
* Sessile or mobile: Some species are stationary, while others can move around using muscles or appendages.
* Important ecological roles: As filter feeders, shellfish contribute to water clarity and play a significant role in nutrient cycling.
Examples of Shellfish:
* Bivalves: Clams, mussels, oysters, scallops
* Univalves: Snails, limpets, conches
* Crustaceans: Crabs, lobsters, shrimp, barnacles
Note: The term "shellfish" can be confusing, as it sometimes refers to only mollusks (bivalves and univalves) and not crustaceans. It's important to clarify context when discussing shellfish.