Some host-parasite relationships of the Acanthocephala, with special reference to the organs of attachment

Abstract 1. 1. A hook-covered proboscis, of extremely diverse shape, size, and armature, is the primary organ of attachment in all species of Acanthocephala. 2. 2. Both morphologically and phylogenetically the short, subglobular proboscis with a relatively small number of hooks seems to be the type from which other modifications have been developed. 3. 3. In many species, the proboscis of the adult worm is identical with that of the infective larva or cystacanth. In some it undergoes progressive change after becoming established in the intestine of the vertebrate definitive host. The most conspicuous examples of this are found in the proboscides of Filicollis and Polymorphus where extreme inflation of the buried proboscis may anchor the worm permanently to the host tissue. Inordinate increase in size of the proboscis of Polymorphus kenti is described for the first time. 4. 4. All three major body divisions are subject to modifications as accessory anchoring devices. Relative development of the proboscis, neck, and trunk in a selected series of genera is discussed and illustrated. 5. 5. In adults of Pomphorhynchus , an enlarged bulb at the anterior end of an attenuated neck, sharply set off from the proboscis, is buried deeply in the host tissue as an anchor. 6. 6. In Filicollis , a similar neck inflation bears the proboscis hooks at its distal pole so that the proboscis is not sharply set off from the neck bulb. 7. 7. Eocollis bears an enlarged anchoring device at the distal end of an attenuated region. These structures superficially resemble those of Pomphorhynchus but both the bulb and the attenuated region are modifications of the anterior region of the trunk. 8. 8. A somewhat similar trunk swelling at the anterior end of a narrow fore-trunk occurs in the genus Bolbosoma . In this genus the effectiveness of the buried trunk bulb is increased by the presence of trunk spines on its surface. 9. 9. The proboscis of males is often smaller, provided with fewer and weaker hooks and often lacks the secondary inflation characteristic of females of the same species. In species showing this type of sexual dimorphism, males are frequently eliminated from the host before females of the same approximate age. 10. 10. Cuticular spines of variable size, appearance, distribution and extent occur on the trunk, especially of some of the more generaliezed Acanthocephala, as secondary organs for attachment. Often they are confined to the anterior region of the trunk where they extend farther posteriorly along the ventral than on the dorsal surface. These help to keep the wormin close contact with theintestinal mucosa of the host. Thereby direct transfer of materials from host to parasite may be facilitated. 11. 11. Especially in Corynosoma , the spine-covered anterior end of the trunk is often modified as an inflated bulb or disc, presenting increased surface for effective contact with host tissue. Partial retraction of the base of the proboscis within this spine-covered disc clampsa fold of host tissue between the proboscis hooks and the trunk spines as a tertiary modification for adhesion to the host intestine.