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Why none of us started specialising branchiae I do not know, but feel that would have been the proper sort of breathing apparatus for such an atmosphere.

Gills or branchiae may be developed by parts of an appendage becoming thin-walled and vascular and either expanded into a thin lamella or ramified.

Mantle oval, covering the head and the greater part of the body; anterior tentacles, ill-developed; branchiae generally retractile.

It is probable that the Silurian scorpion was an aquatic animal, and that its respiratory lamellae were still projecting from the surface of the body to serve as branchiae.

The appendages of the body are reduced to branchiae, present in certain forms.