The Life Cycle and Larval Development of Octospinifer macilentis (Acanthocephala: Neoechinorhynchidae)

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Abstract
The acanthocephalan, Octospinifer macilentis, is an intestinal parasite of the common sucker, Catostomus commer-soni. Ostracods, Cyclocypris serena, Physocypria pustulosa, and Cypridopsis sp., along with other arthropods, were fed infective ova. Only C. serena susstained infections until cystacanth larvae developed. Eggs hatched inside the intermediate host within 4 hr. and liberated spindle-shaped acanthors with anterior spines. Attempts to induce hatching artificially by proteolytic enzymes failed. Motile acanthors penetrated the gut within 24 hr. After 4 days in tissues dorsal to the gut, acanthors moved into the hemocoel and by the 5th day lost their spines and became immobile. Acanthella stages revealed changes in the entoblast: the anterior section gave rise to the brain, proboscis receptacle, and proboscis muscles; the posterior section formed the genital complex; between the two sections the pseudocoel appeared. The epidermis, formed from the peripheral cytoplasm, contained nine giant nuclei[long dash]six remained in the epidermis and three moved into the lemnisci after 25 days. The octamerous nature of the proboscis became apparent after 20 days when the hooks, in three rows of eight each, developed from the dermis. Differentiation of the genital apparatus distinguished the sexes by day 20 when two testes appeared within a single ligament sac and ovarian masses differentiated within two ligament sacs. By day 30 the proboscis of the cystacanth was capable of inversion and protrusion, epidermal nuclei were in their characteristic sites, and the gonads were distinct. No transport host was required to carry the cystacanth to a definitive host. In this respect, O. macilentis differs from Neoechinorhynchus cylindratus and N. emydis Cato-stomus commersoni was successfully infected by force-feeding with parasitized ostracods. Maxostoma aureolum and Notropis dorsalis failed to acquire infections. In the definitive host, worms were established in the intestine within 4 hr. Maturity was reached after approximately 8-10 weeks for males and 16 weeks for females.