Chambered cuticle, pellicles, strange sensilla, and extraordinary muscle arrangements: a study of the micropterigid larval trunk (Lepidoptera: Micropterigidae).

The larvsal trunk wall of Sabatinca chalcophanes (Meyrick, 1885), representing the "sabatincoid morphotype," is described (brightfield and polarization microscopies, scanning and transmission electron microscopies). Eight sensillum types are identified, including four previously undescribed subventral and ventral kinds. The cuticle is nonsolid, the exocuticle being chambered in a honeycomb-like fashion with chamber walls apparently secreted along epidermal cells boundaries. The chamber contents open to the exterior via minute pores in the chamber roofs. A space between endo and exocuticle communicates with the chamber interiors via pores in the chamber floors; the dense endocuticular surface in places form thickened domes. On the lower trunk region, lateral chamber walls are highly porous (lattice like), hence their contents are continuous; individual chamber roofs here are markedly convex, and the external trunk surface, therefore, papillate. The trunk surface is more or less completely covered by a pellicle, likely formed by exudates from the exocuticular chambers. Unusually for Lepidoptera all trunk muscles are slender strands covering a modest proportion of the inner trunk surface. Conspicuous insertion "nodes" are located at lateral and ventral segmental boundaries, ventromedially near segmental midlengths, and paramedially on the dorsum behind segmental midlengths. Overall similar cuticular specializations are also present in the distantly related Micropterix, strongly supporting micropterigid monophyly.