Knowra Bilateria Bilateria Bilateria is the animal clade whose members develop distinct left and right sides and usually an anterior–posterior axis. It includes most animal diversity, including vertebrates, insects, mollusks, and worms.
Bilateral symmetry : A body plan with corresponding left and right sides arranged around a single plane. It names Bilateria’s defining anatomical pattern, though some members lose it secondarily.
Hox genes : A family of genes encoding transcription factors that help specify positional identity along animal body axes. Their conserved roles help pattern regions along bilaterian anterior–posterior axes.
Ediacaran biota : A diverse assemblage of mostly soft-bodied organisms preserved in rocks from the Ediacaran Period. Some Ediacaran fossils may record early bilaterian forms, though their relationships remain debated.
Cnidaria : An animal phylum including jellyfish, corals, and sea anemones, many with radial symmetry and stinging cells. Cnidarians are the closest major living animal lineage outside Bilateria in common phylogenetic hypotheses.
Cephalization : The evolutionary concentration of sensory organs and nervous tissue at an animal’s front end. Directional movement in many bilaterians favors concentrating sensing and neural control near the head.
Anterior–posterior axis : The body axis running from the head or front end toward the tail or rear end. Its development commonly gives bilaterians a distinct front and back.
Wnt signaling pathway : A conserved cell-signaling system involved in embryonic development, tissue maintenance, and cell fate decisions. Wnt signals help establish and pattern body axes across diverse bilaterians.
Kimberella : A fossil organism from the Ediacaran Period, often interpreted as a possible bilaterian. Its body and associated feeding traces provide evidence relevant to early bilaterian evolution.
Ctenophora : A phylum of marine animals called comb jellies, which move using rows of ciliary plates. Comb jellies provide another comparison for reconstructing early animal evolution outside Bilateria.
Central nervous system : The part of a nervous system consisting chiefly of a brain and spinal cord or nerve cord. Bilateral body organization is associated with diverse centralized nervous systems, though not all bilaterians have one.
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