Hausellate mouthparts

Haustellate means that the mouthparts of an insect are modified for sucking.  Haustellate mouthparts are usually in the form of some sort of tube called a beak or rostrum.  Depending on the food that an insect feeds on, other modifications are present.  For instance, many insects' mouthparts have a sharp part of the beak which allows them to peirce their food source.  This may be for skin (as with mosiquitos) or plant derma (as with cicadas).  Other insects, such as lepidoptera (butterflies), simply have tubes through which they suck nectar from flowers.  There is no piercing action, simply siphoning of the liquid.
Opisthognathous means that the mouthparts are directed backward, under the insects body.  Pictured here is a giant waterbug (hemiptera) which exhibits these types of mouthparts.