Mouthpart palp sensilla of basal Trichoptera families

A comparative SEM study of palp sensory surfaces in 25 caddisfly species representing seven families reveals seven types of sensilla: long trichoid, blunt chaetoid, campaniform, mushroom-like pseudoplacoid, petaloid, thick basiconic and thin basiconic sensilla. Long trichoid and chaetoid sensilla are present on all segments of both pairs of palps. First and second segments of maxillary palps bear groups of long and sclerotised chaetoid sensilla on their medial surface. Other segments of maxillary palps and all segments of labial palps have shorter and thinner chaetoid sensilla mainly on their ventromedial surfaces. Campaniform sensilla usually occur on the first segment of labial palps and second segment of maxillary palps. Mushroom-like pseudoplacoid sensilla may occupy all palp segments or only distal ones. Petaloid sensilla form sensory fields on apical segments of both pairs of palps in most studied species. Thick basiconic sensilla occur only in apical sensory complexes on tips of maxillary and labial palps. A comparison with the Lepidoptera suggests the similarity in palp sensilla and conservative evolution of the palp surface. The reconstructed ground plan for the palp sensory surfaces in Trichoptera and Amphiesmenoptera is provided.