Bivalves are Mollusks

The phylum MolluscaMollusca:
The phylum of the animal kingdom, including the classes Cephalopoda, Gastropoda, Bivalvia, Scaphopoda, Polyplacophora, Monoplacophora, Caudofoveata, and Solenogastres. These animals have an unsegmented bilateral body, with most of the organs and parts paired, but not repeated serially. Mollusks are defined by a tissue called the mantle, which forms the shell and encloses most organs. Most mollusks possess a calcareous shell, which can be univalve, bivalve, or multivalve.
includes clams, snails, slugs, nudibranchs, squid, octopuses, tusk shells, chitons, and many others that are all generally called mollusksMollusk:
A member of the phylum Mollusca; also spelled mollusc (most especially in the United Kingdom).
. Some, but not all, of these also go by the more common term "seashells." Most mollusks bear a shell of one or more parts made of calcium carbonate. There are approximately 120,000 species of living mollusks, and many more extinct species recorded as fossils back to the Cambrian Period over 500 million years ago. Mollusks are the second largest phylum on Earth, only surpassed by the insects, and are the largest taxonomic group in the sea.

Scientists currently recognize eight classes of mollusks: Monoplacophora (primitive limpets, not shown), Gastropoda (snails and slugs), Bivalvia (see below images), Cephalopoda (squids and octopuses), Polyplacophora (chitons), Scaphopoda (tusk shells), and two classes of worm-like mollusks (Caudofoveata, Solenogastres) generally called “aplacophorans.”


White-Lipped Landsnail, Cepaea hortensis.

Red Slug, Arion rufus.

Nudibranch, Nembrotha lineolata.

Cephalopoda and Polyplacophora

White-Spotted Octopus, Octopus macropus.

Caribbean Reef Squid, Sepioteuthis sepioidea.

Green Chiton, Chiton glaucus.

Scaphopoda and “Aplacophorans”

Tusk Shell, Antalis vulgaris.

Aplacophoran, Epimenia babai.

The molluscan class BivalviaBivalvia:
A class of the phylum Mollusca including species with two shells hinged together, a soft body, and lamellate gills. Commonly called bivalves.
includes clams, scallops, mussels, oysters, and their relatives — all generally called bivalves, pelecypods (in older literature, and still used by many paleontologists), or more commonly “clams.” There are approximately 20,000 living species of bivalves, which ranks them second only to gastropods in terms of total species diversityDiversity:
The variety of species in a sample, community, or area.
. All bivalves are aquatic, either marine or freshwater, and they play a variety of important ecological roles. Bivalves are familiar objects (often collected as seashells) and are therefore excellent primary study organisms for engaging students.

Dipper Clam, Cuspidaria latesulcata.

Heart Cockle, Fragum unedo.

Giant Clam (Tridacna sp.)

Sydney Rock Oyster, Saccostrea glomerata.

Freshwater mussel, Hemistena lata.