Arthropod mouthpart

The mouthparts of arthropods have evolved into a number of forms, each adapted to a different style or mode of feeding. Most mouthparts represent modified, paired appendages, which in ancestral forms would have appeared more like legs than mouthparts. In general, arthropods have mouthparts for cutting and chewing, piercing and sucking, siphoning, and filtering. This article outlines the basic elements of four arthropod groups: insects, myriapods, crustaceans and chelicerates. Insects are used as the model, with the novel mouthparts of the other groups introduced in turn. Insects are not, however, the ancestral form of the other arthropods discussed here.

Insect mouthparts exhibit a range of forms. The earliest insects had chewing mouthparts. Specialisation includes mouthparts modified for siphoning, piercing, sucking and sponging. These modifications have evolved a number of times. For example, mosquitoes (which are flies) and aphids (which are bugs) both pierce and suck; however, female mosquitoes feed on animal blood whereas aphids feed on plant fluids. This section provides an overview of the individual mouthparts of chewing insects.

The labrum is a flat extension of the head (below the clypeus), covering the mandibles. Unlike other mouthparts, the labrum is a single, fused plate (though it originally was—and embryonically is—two structures). It is the upper-most of the mouthparts and located on the midline. It serves to hold food in place during chewing by the mandibles and thus can simply be described as an upper lip.

Chewing insects have two mandibles, one on each side of the head. They are typically the largest mouthpart of chewing insects, being used to masticate (cut, tear, crush, chew) food items. They open outwards (to the sides of the head) and come together medially.

Paired maxillae cut food and manipulate it during mastication. Maxillae can have hairs and "teeth" along their inner margins. At the outer margin, the galea is a cupped or scoop-like structure, which sits over the outer edge of the labium. They also have palps, which are used to sense the characteristics of potential foods.

The labium is a single structure, although it is formed from two fused secondary maxillae. It can be described as the floor of the mouth and functioning in close the mouth of the insect. With the maxillae, it assists manipulation of food during mastication.

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