Raptorial phantom midges

The predaceous larvae of phantom midges (Chaoboridae) are almost completely unpigmented and weakly sclerotized. They live exclusively in standing water and feed on copepods and water fleas. They capture the prey with raptorial antennae; a unique mechanism within Diptera. This unusual feature and the unclear homology of different larval head structures induced us to investigate the mouthparts and the internal cephalic structures of the larvae of Chaoborus crystallinus De Geer 1776. The head is strongly compressed laterally. The closely adjacent antennae have a similar function as the mantid raptorial forelegs. They are 1-segmented; elongated and strongly sclerotized. Their location in front of the compound eyes ensures a good coordination in the prey-catching process. The abduction is caused indirectly: the hemolymph pressure is increased by the contraction of the M. transversi rostralis. The two pairs of labral retractors also contribute by stabilizing the membranous mouth region. The mouthparts are located on the ventral side. The labrum is a very narrow; strongly elongated and largely sclerotized on the ventral side of the head. It is inserted on a small trapezoid ventral clypeus. Its unsclerotized parts are equipped with brushes. The elongated dorsal sclerite previously addressed as clypeofrons is in fact only the frons. The labium and the maxillae are largely reduced. The function of the mandibles (abducted by M. abductor mandibulae) and the labrum (depressed by M. adductor epipharyngis) is to hold down the prey. During the capturing process; M. retractor antennae accomplishes the adduction of the antennae. The labrum is elevated by M. abductor epipharyngis and the mandibles adducted by M. adductor mandibulae. The laciniae mobilis form a rake confining the prey in the space between them. A close relationship of Chaoboridae and Dixidae is confirmed. A sisiergroup relationship with the former family is more likely.