Molluskien

Molluskien is the phylum Mollusca, a highly diverse group of invertebrate animals. It includes the gastropods (snails and slugs), bivalves (clams, mussels, oysters, scallops), cephalopods (squids, octopuses, cuttlefish), polyplacophorans (chitons), and scaphopods (tusk shells). Mollusks occur in marine, freshwater, and terrestrial habitats, from deep oceans to damp terrestrial environments.

Anatomy and organization: Mollusks are triploblastic and coelomate. Most have a mantle, a fold of tissue that often secretes a calcium carbonate shell. A ventral muscular foot is used for movement, and a radula serves as a feeding organ in many groups (though bivalves typically lack a radula). The mantle cavity houses gills or lungs. Circulatory systems range from open to closed, being closed in most cephalopods.

Diversity of life histories: Mollusks show a wide range of feeding strategies, including grazing on algae, filter feeding, scavenging, and predation. Reproduction varies; many species release free-swimming larvae, while others brood young or reproduce by direct development. Cephalopods are among the most mobile and intelligent invertebrates.

Shells and evolution: The shell is a characteristic feature for many mollusks but some lineages have lost it or retained an internal shell. The fossil record for Mollusca extends back to the early Cambrian, and the group has diversified into numerous forms through hundreds of millions of years.

Human relevance and conservation: Mollusks are important for food (such as clams and snails), shells and pearls, and as model organisms in biology. Many species face threats from habitat loss, pollution, overharvesting, and ocean acidification, making conservation and sustainable management important.