One important concept is that typically used reinforcing (post-tensioning tendons and shrinkage-compensating concrete reinforcement are the exceptions) will not prevent the concrete from cracking. The reason for this is that the reinforcing cannot begin to start resisting significant tension until the concrete cracks.
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.he mantle also secretes the shell, in those mollusks that have one. In many gastropods and cephalopods, the mantle is brightly colored and important for communication. In giant clams, the outer mantle tissue is colonized by symbiotic algae that provide their host with food energy in exchange for shelter.
In fishes the gills are located in gill chambers at the rear of the mouth (pharynx). Water is taken in through the mouth, is forced through openings called gill slits, and then passes through the gill clefts, spaces between the ranks of delicate gills, bathing them continuously.n the process of animal evolution, gills first appear in annelid worms, in the form of simple, pectinate, or bipinnate plates and simple or branched filaments. They are located on the lateral motor appendages (in freely moving forms) or at the head end of the body (in those living in tubes).