Marine mollusca is also known as Limpets.

Explanation:
Marine mollusca is a broad term that refers to a diverse group of marine organisms belonging to the phylum Mollusca. Molluscs are a large and diverse group of invertebrates that include animals such as snails, clams, octopuses, and squid. They are found in all marine environments, from the deep sea to the intertidal zone.

Characteristics of Marine Mollusca:
- Marine molluscs have a soft body, usually protected by a hard shell made of calcium carbonate.
- They exhibit a wide variety of body shapes and sizes, ranging from tiny snails to giant squids.
- Molluscs have a muscular foot that they use for locomotion.
- They have a radula, a specialized feeding structure that helps them scrape or rasp food particles.
- Most marine molluscs have a mantle, which is a thin layer of tissue that secretes the shell.
- They have a well-developed nervous system and sensory organs, such as eyes and tentacles.

Diversity of Marine Mollusca:
Marine molluscs exhibit incredible diversity in terms of their morphology, behavior, and ecology. They occupy various ecological niches and play important roles in marine ecosystems.

Examples of Marine Molluscs:
- Limpets: Limpets are a type of marine mollusc that belong to the class Gastropoda. They are characterized by their conical or flattened shells and strong muscular foot, which allows them to cling tightly to rocks in the intertidal zone. Limpets feed on algae by scraping them off rocks using their radula.
- Crabs: Crabs are crustaceans and not molluscs. They belong to the phylum Arthropoda and are known for their hard exoskeleton and ten legs. They are often found in marine environments, where they play important roles in the food web.
- Puppets and shrews: Puppets and shrews are not related to marine molluscs. They are land-dwelling mammals and are not part of the phylum Mollusca.

In conclusion, marine mollusca is a term that refers to a diverse group of marine organisms belonging to the phylum Mollusca. Limpets are one example of marine molluscs, known for their conical or flattened shells and their ability to cling to rocks in the intertidal zone.