Comparative investigations of the morphology and chemical composition of the eggshells of Acanthocephala. I. Macracanthorhynchus hirudinaceus (Archiacanthocephala).

Eggshells of Macracanthorhynchus hirudinaceus (Archiacanthocephala) were investigated for their fine structure as well as their chemical composition. The acanthor larvae are surrounded by four eggshells (E1-4) separated by interstices of low electron density (G1-4). As these envelopes are secreted in different sequences and are reinforced to different degrees, their appearance varies throughout development. The outermost eggshell (E1) of this species has a tripartite appearance; it contains neither chitin nor keratin. Keratin appears in E2 and E3. It was localized electron microscopically using anti-keratin and, for the first time by fluorescence microscopy with the bromobimane reaction. Keratin occurs in two forms: in the second envelope (E2) it consists of twisted struts of filaments, whereas in the innermost sublayer of the third envelope (E3) it shows a conspicuous cross-striation; in the first and second sublayers of E3, neither keratin nor a discernible structure is present. Chitin occurs in the innermost layer (E4). The interstices G1, G3 and G4 seem to contain glycoproteins, whereas interstice G3 seems to contain some type of carbohydrate. After the extraction of proteins including keratin with sodium dodecyl sulfate (SDS) and dithiothreitol (DTE) only layers E1 and E4 remained.