Physiology of Finfish and Shellfish (2+1)

2.1.32. Anatomy of the respiratory system of cephalopods

Cephalopods are molluscs, but, they have two different kinds of morphology; nautiloidea possess external shell cupereas the rest possess a reduced internal shell.

The tetrabranchia

They possess an external shell and two pairs of gills.

The dibranchia

They possess either a much reduced internal shell or it is totally missing and they possess a single pair of gills.

Mechanism of respiration

The circulation of water through the mantle not only produces the power for swimming but also provides oxygen for their gills.

Description of cephalopod gills

The surface area of cephalopod gills have been much increased by a type of folding and is not ciliated as in other molluscs. The gills of cephalopods are supported by a speleton of roluest filerous proteins; the lack of mucopolysaccharides distinguishes this matrix from cartilage.

Gills are also involved in excretion with NH₄⁺ being exchanged for K⁺ from seawater overall, cephalopod gills, found attached to the ventral surface of mantle cavity are much more efficient than these of other molluscs.

Respiratory pigment

Cephalopods use “haemocyanin” – a copper containing protein for oxygen transportation. As a result, their blood is colerless cehen deoxygenated and turns blue upon exposure to air.