Cosmoid scales

Australian Lungfish scale Click to enlarge image
A scale from an Australian Lungfish in the fish collection. Image: Carl Bento
© Australian Museum

Fast Facts

Cosmoid scales are found in the Lungfishes (family Ceratodidae) and some fossil fishes.

Australian Lungfish scales

Scales of an Australian Lungfish from the fish collection.

Image: Carl Bento
© Australian Museum

Cosmoid scales are similar to placoid scales and probably evolved from the fusion of placoid scales. They consist of two basal layers of bone, a layer of dentine-like cosmine, and an outer layer of vitrodentine.

Australian Lungfish

Lungfish are named for their ability to breathe air by coming to the surface when water is stagnant or the quality is low. The Australian Lungfish is unique in having only a single lung – all other species have a pair. Lungfish can grow to 1.5 metres in length and 40 kilograms in weight.

Image: Stuart Humphreys
© Australian Museum

As the fish grows each scale becomes larger as new bone is added to the basal layers.

Reference:
Helfman, G.S., Collette, B.B. & D.E. Facey. 1997. The Diversity of Fishes. Blackwell Science. Pp. 528.