A taxonomic grouping or classification of animals that lack an allantois during embryonic development.
From Greek 'an-' (without) + 'allantois' + Latin '-dea' (belonging to). This term developed in 19th-century zoological classification.
This grouping would include fish, amphibians, and certain other creatures whose embryos don't need an allantois, helping scientists organize the tree of life based on developmental features!
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