Fish belong to the phylum Chordata, which includes all animals with a dorsal nerve cord. Most fish exhibit bilateral symmetry, meaning they can be divided into two equal halves along a single plane.
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Most animals in the Mollusk phylum have bilateral symmetry, where their body can be divided into two equal halves along a single plane. This symmetry allows for more efficient movement and sensory abilities.
Symmetry in animals of the phylum is typically categorized as radial or bilateral. Radial symmetry is when an organism can be divided into equal halves in multiple planes around a central axis, like a sea anemone. Bilateral symmetry is when an organism can be divided into two equal halves along just one plane, like a human.
The phylum Porifera (sponges) is the only animal phylum that lacks true tissues and symmetry. Sponges are simple multicellular organisms with specialized cells, but they do not have tissues that are organized into distinct structures like other animals. Additionally, sponges exhibit asymmetry rather than bilateral or radial symmetry found in other phyla.
The phylum name for planarians is Platyhelminthes, which includes flatworms like the planarian. They are characterized by their flattened body shape and bilateral symmetry.
The phylum Echinodermata has radial symmetry as adults. These organisms include sea stars, sea urchins, and sand dollars, among others. Radial symmetry means that body parts are arranged around a central axis, like the spokes of a wheel.