Acanthocephala

Abstract

Abstract The nervous system of the 1150 species-containing Acanthocephala is strongly influenced by their parasitic lifestyle. Also known as ‘thorny-headed worms’, these few-centimetre-long animals are endoparasites, having insects or crustaceans as intermediate hosts and vertebrates as final hosts. The basic structural pattern of the nervous system is common to all Acanthocephala. Nevertheless, there are significant differences in numbers of cells and arising nerves from the cerebral ganglion present in the various acanthocephalan groups, i.e. Archiacanthocephala, Eoacanthocephala, and Palaeacanthocephala. A cerebral ganglion lies behind the characteristic revertible proboscis, and normally consists of less than 100 cells. It is subdivided into a peripheral layer of pericarya, and a central neuropil, which innervate the proboscis and the trunk. Male acanthocephalans feature a pair of genital ganglia at the penis base, comprising between 15 and 30 cells. In addition, a bursal ganglion was found in the posterior end of males. Like the genital ganglia, it is assumed to innervate the muscles that are involved in the eversion and erection of the bursa. In 1989, a vaginal ganglion was discovered in female acanthocephalans. This may control the vaginal musculature and the body wall musculature associated with the region of the gonopore. Based on the parasitic lifestyle of Acanthocephala, sense organs are poorly developed, as far as is known. Acanthocephalans have posterior receptors which are thought to facilitate copulation. Further, in the anterior body region, paired lateral sensory organs and an apical sensory organ can be found.