Feeding in Invertebrates Mussel Mosquito Butterfly Aphid Housefly

Many bivalve mollusks, for example the mussel Mytilus edulis, feed on particles suspended in the surrounding water. This is called filter feeding

When it is covered by seawater, the two shells open slightly, allowing water to enter the body of the mussel From this extend a pair of short tubes, called siphons A current of water is drawn into the “lower” siphon, then across the gills and out through “top” siphon This movement is powered by the combined effect of many cilia: projections from cells lining the spaces inside the mussel's shell.

The gills hang down like net curtains, trapping small particles as well as extracting dissolved oxygen from the water Cilia on the gills send a current of mucus down each strand and then onward towards the mouth Any food particles of a suitable size that are trapped are ingested by the mouth and digested in the gut Incidentally, this is not unlike the means by which foreign particles including bacteria are trapped in mucus in the human respiratory system, and then taken up to the throat, swallowed and digested in the stomach.

Picture of the gill of a mussel

Feeding in Mosquitoes While mosquitoes are able to survive on plant juices and nectar, the females require blood to develop eggs (with a few rare exceptions). Mosquitoes feed on the blood of mammals and birds Bloods contains the food that has been ingested, digested and absorbed by the animal that the mosquito is feeding on.

The mosquito's mouth is made up of bristles and tubes. The bristles first poke a tiny hole in the skin and then two tubes are inserted into the hole. Saliva flows down through one tube and the blood is sucked up through the other. The saliva has an anticoagulant (chemical that stops blood clotting) that allows the blood to flow easily up through the tube. The proteins contained in the saliva are left behind in the host and cause the skin to itch.

Mosquitoes and Malaria The saliva of the mosquito may contain parasites that cause diseases, such as malaria. Parasites are organisms that live in or on another organism (called the host) and obtain food from it. The malarial parasite is a single-celled organism (Protoctistan) that feeds and reproduces inside human blood cells. Rupture of the blood cells causes the severe fever associated with Malaria. Mosquitoes enable the parasites to be transmitted from one person to another.

Feeding in the Housefly The fly produces saliva which it releases onto food The food dissolves in the saliva Using muscles, the fly pumps the liquefied food up into its mouth The mouthparts have a large surface area so food can be dissolved and ingested quicker.

Feeding in Aphids Aphids feed on the sucrose solution inside the phloem They have sharp, pointed, hollow mouthparts that are long enough to go through the epidermis of stems and leaves and into the phloem.

Feeding in Butterflies Adult butterflies feed on the nectar - sugar solution – produced by flowers They have very long mouthparts that are kept coiled up when not in use The mouthparts have to be long to reach the nectary which is often deep down inside the flower