wear your heart on your sleeve. to make your feelings and opinions obvious to other people John's always worn his heart on his sleeve, so there's no doubt who he'll be supporting. See also: heart, on, sleeve, wear. Related vocabulary: wear something on your sleeve.
In many bivalves and snails, and in cephalopods, part of the mantle is modified into a siphon, which can be used to pump water through the mantle cavity for respiration, feeding and/or jet propulsion. Freshwater and marine mollusks have gills (called ctenidia) for respiration, located in the mantle cavity. In most bivalves, these are enlarged and serve to trap food particles as well (Morton 1983).
Gills are evaginations of the body surface. Some open directly to the environment; others, as in fishes, are enclosed in a cavity. In contrast, lungs represent invaginations of the body surface. Many invertebrates use gills as a major means of gas exchange; a few, such as the pulmonate land snail, use lungs. Almost any thin-walled extension of the body surface that comes in contact with the environmental medium and across which gas exchange occurs can be viewed as a gill.