Fish belonging to the order Abdominales, characterized by having abdominal fins attached to the belly rather than near the gills.
From Latin 'abdomen' (belly) plus '-alis' (relating to), plus nominal '-s'. Named for the anatomical position of their fins in classical ichthyology.
Early fish classification literally carved up fish by where their fins attached—'abdominals' have belly fins while other groups have them elsewhere, creating a taxonomy that's anatomically honest but now considered outdated by modern phylogenetics.
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