Relating to or belonging to animals that lack an allantois, or describing the characteristic of not developing an allantois.
From 'anallantoidea' + English '-an' (relating to). This scientific adjective emerged in comparative embryology.
When scientists compare embryos of different animals, they notice that some are 'anallantoidean'—this developmental difference is actually a major clue to understanding how different animal groups are related on the evolutionary tree!
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