Dibranchia

former cephalopod taxon

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June 25, 2026

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Dibranchia is a taxonomic group that includes squids and octopuses, distinguishing them from the genus Nautilus. This classification is based on having two gills, two auricles, and two nephridia, along with an ink-expelling apparatus. Living cephalopods, except for Nautilus, fall under this category.1

Historically, early classifications divided living cephalopods into Octopoda and Decapoda, both placed within Dibranchia. This contrasted with fossil forms, which were considered Tetrabranchia due to Nautilus possessing four gills instead of two. While this classification has been modified, the distinction between two-gilled and four-gilled cephalopods remains a key point in their study. The term "dibranchiate" refers to organisms with two gills.21

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Critical appraisal
…were both placed in the Dibranchia, in contrast to all fossil forms, which were considered as Tetrabranchia because Nautilus has four gills rather than two. This unnatural classification, accepted by the French zoologist Alcide d’Orbigny in 1838, was gradually modified through the efforts of the Swiss zoologist Adolph Naef and…
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…were both placed in the Dibranchia, in contrast to all fossil forms, which were considered as Tetrabranchia because Nautilus has four gills rather than two. This unnatural classification, accepted by the French zoologist Alcide d’Orbigny in 1838, was gradually modified through the efforts of the Swiss zoologist Adolph Naef and…
Read More