Physiology of Finfish and Shellfish (2+1)

2.1.36. Other gill arrangements

 In many gastropods, the filamentous gill has been replaced by a “Plicate”, or folded, structure. Many of these gastropods have also undergone of de-torsion, with the mantle cavity and gill shifting round to the right side of the body. This type of arrangement is found in the bubble shells and also in the sea hares, which also possess an exhalant siphon that projects fouled water away from the body.

In the nudibranchs the mantle cavity and the original gill have disappeared altogether. In stead, the upper surface of the body has numerous club – shaped or branched projections called cerate that function as secondary gills. Secondary gills are also present in the unrelated genus Patella, in which they are found as folds within the mantle cavity.

Some smaller gastropods have neither true gills nor cerate. The genus Lapeta, users whole of the mantle cavity as a respiratory surface, while many sea butterflies respire through their general body surface.