Morphological adaptations of the head and mandibles of some coleopterous larvae burrowing solid substrates (Coleoptera).

Abstract

The author describes 4 types of morpho-functional adaptations of head capsule and mandibles of the coleopterous larvae actively breaking soil, wood and other natural solid substrates. In some larval forms the head capsule and mandibles are used for digging the substrate. These organs are often modified according to this function. 1st type - hypognathous larvae burrowing in the substrate by the external edges of the mandibles. In some cases sclerotized flattened ridges on the lateral edges of the mandibles are developed. - 2nd type - larvae with modified mandibles resembling a scraper: the distal part of the mandibles is flattened, denticled or chiselshaped. There is a tendency to reduce the head capsule and to have it enclosed by the prothorax. - 3rd type larvae with a prognathous flattened wedge-shaped head. They dig the substrate with the anterior margin of the head capsule and the lateral edges ofthe mandibles. - 4th type - larvae with reduced head completely drawn into the prothorax. The digging of the substrate is carried out by mean of the flattened wedge-shaped prothorax and denticled apices of the mandibles. Each morpho-dynamic type is characterized by a specific mode of burrowing the substrate and an appropriate complex of morphological features in the head structure. Within each morpho-dynamic type there is a clearly expressed correlation between the shape of the digging organs, their local orientation and the mode of their operation. The development of similar morpho-dynamic types in different systematic groups of coleopterous larvae is a consequence of this convergence.