dipnoi

Definitions

A subclass of fishes, by some considered to be a peculiar class of vertebrates intermediate between fishes and batrachians, and by others an order of fishes (by some ranked as a suborder of ganoid fishes), containing the lung-fishes of the genera Lepidosiren and Protopterus (Dipneumona) and Ceratodus (Monopneumona), and many extinct relatives.

noun plural (Zoöl.) A group of ganoid fishes, including the living genera Ceratodus and Lepidosiren, which present the closest approximation to the Amphibia. The air bladder acts as a lung, and the nostrils open inside the mouth. See ceratodus, and Illustration in Appendix.

noun bony fishes of the southern hemisphere that breathe by a modified air bladder as well as gills; sometimes classified as an order of Crossopterygii

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Silurian and the coal measures, we find very plentiful remains of certain fish called the dipnoi, of which group three genera still survive; they display, in numberless features of their anatomy, transitional characters between true fish and amphibia.

Text Book of Biology, Part 1: Vertebrata 1906
Of the older dipnoi (Paladipneusta) we have now only one specimen, the remarkable Ceratodus of East Australia; its amphiblastic gastrulation has been recently explained by Richard Semon (cf. Chapter 2.21).

The Evolution of Man — Volume 1 Ernst Heinrich Philipp August Haeckel 1876
So again, while the group of fishes, termed ganoids, is, at the present time, so distinct from that of the dipnoi, or mudfishes, that they have been reckoned as distinct orders, the Devonian strata present us with forms of which it is impossible to say with certainty whether they are dipnoi or whether they are ganoids.

The Rise and Progress of Palaeontology Thomas Henry Huxley 1860
5Google “Diabolepis and its relationship to dipnoi”

Panderichthys rhombolepis - The Panda's Thumb 2005