Fig. 2. Life cycle of common acanthocephalan species (cf. Table 1). A Macracanthorhynchus hirudinaceus; B Polymorphus minutus. 1 The adults live in the intestine of their final hosts, being attached by their hooked proboscis. The penetration of the intestinal wall leads to inflamed protrusions (IP) appearing along the outer side. 2 After copulation the adult females excrete eggs for several months (patent period). These eggs are passed fully embryonated (i.e. they contain the hooked acanthor larva) with the feces of the host. 3-6 Intermediate hosts ( Gammarus spp. or beetle larvae) become infected by ingesting infective eggs. Inside the intestine the acanthor is released from the egg (4; RA), enters the body cavity and is transformed into an acanthella larva (5). The latter matures within 60-95 days (in M. hirudinaceus) and is described as an infective larva (cystacanth). Infection of the final hosts occurs when they swallow infected intermediate hosts. The young worms reach sexual maturity within 60-90 days in M. hirudinaceus (after 20 days in Polymorphus minutus) and start egg production (= end of prepatent period). AC, acanthor; BH, body hooks; IP, inflamed protrusion of IW; IW, intestinal wall; PH, proboscis hooks; RA, released acanthor
Fig. 3. Life cycle of two common acanthocephalan species parasitizing fish. A Neoechinorhynchus rutili; B Acanthocephalus anguillae. 1 Adults are attached to the intestinal wall of their final hosts, trouts (A) or chubs and other fish (B). 2 Fully embryonated eggs are passed with host's feces. 3-6 Intermediate hosts (A Asellus aquaticus, B ostracod crustaceans) are infected by uptake of eggs. Inside their intestine the acanthor larva (4) is released from its eggshell, enters the body cavity and becomes transformed into the acanthella larva (5). This stage differentiates to the infective larva without encystation in about 30-60 days (6) depending on outer conditions. Final hosts are infected by swallowing intermediate hosts. In A. anguillae a paratenic host may also become involved. When bleaks and some other fish ingest intermediate hosts (Asellus aquaticus), the infective larva enters the fish viscera, but there is no further development, but quick depeneration. Infected paratenic hosts may be a second source of infection for the final host. Neoechinorhynchus rutili and A. anguillae reach sexual maturity in about 20-30 or 40-60 days respectively (prepatent period). Adults live only for about 2-3 months (patent period). AC, acanthor; IP, inflamed protrusion of IW; IW, intestinal wall; LM, lemniscus; PH, proboscis hooks