What defines the body plan of Bilateria?
Bilateria is defined by embryonic development that establishes bilateral symmetry along a single axis. This arrangement places the belly on one side and the back on the other while mirroring left to right.
Questions about Bilateria
Short answers, pulled from the story.
When did the first evidence of Bilateria appear in the fossil record?
The earliest confirmed bilaterian fossils date to approximately 555 million years ago with Kimberella. Earlier candidates like Ikaria wariootia lived between 571 and 539 million years ago within Ediacaran sediments.
How do Protostomes differ from Deuterostomes during embryonic development?
Protostomes develop where the blastopore becomes the mouth while Deuterostomes form with the blastopore becoming the anus. This fundamental difference shapes how each group constructs its internal anatomy.
Who proposed the Archicoelomata hypothesis regarding the urbilaterian?
Ernst Haeckel described early versions of this idea in 1872 as the Gastraea. Claus Nielsen later refined these concepts into the Trochaea model.
What percentage of known animal species are classified as Bilateria today?
Bilaterians constitute over 98% of all known animal species today. Their rapid diversification occurred during the late Ediacaran and Cambrian periods making them the dominant lineage among animals.