The phylum Acanthocephala is comprised of more than 1000 species of pseudoceolomic helminths, which, as adults, occur exclusively in the vertebrate small intestine. The most commonly parasitised definitive hosts are bony fishes, followed by birds, mammals and rarely amphibians and reptiles. Acanthocephalans are characterised by the possession of a head called a proboscis bearing hooks and spines that enable them to attach to the intestinal wall of their definitive host. Acanthocephalans are dioecious and exhibit sexual dimorphism. As an adaptation to parasitism, acanthocephalans have secondarily lost their digestive system and acquire their nutrients by direct absorption across the body wall. Acanthocephalans are primarily osmoconformers, and respiration and excretion occur primarily by diffusion across the body wall. All acanthocephalans exhibit an indirect life cycle utilising an arthropod intermediate host. Despite their sometimes large size, acanthocephalans cause relatively little pathology. Although very rare, human infection does occur. Molecular evidence suggests that Acanthocephalans are phylogenetically most closely aligned with the rotifers.

Key Concepts:

  • As adults, acanthocephalans are parasites of vertebrates.

  • Acanthocephalans have secondarily lost their digestive system as an adaptation to parasitism.

  • Acanthocephalans are closely related to the rotifers.

  • Approximately 1200 species of acanthocephalans have been described.

  • Acanthocephalans get their name from the spiny head called a proboscis.

Keywords: Noneacanthocephala; parasite; parasitism; helminthes

Figure 1.

Proboscides of: Centrorhynchus robustus from a northern spotted owl Strix occidentalis, upper left, bar=250 μm. Redrawn from Richardson and Nickol . Polymorphus cucullatus from a hooded merganser Lophodytes cucullatus, upper right, bar=500 μm. Redrawn from Van Cleave and Starrett . Oligacanthorhynchus tortuosa from a Virginia opossum (Didelphis virginiana), centre, bar=100 μm. Redrawn from Richardson . Mediorhynchus centurorum from a red‐bellied woodpecker Centurus carolinus, lower left, bar=220 μm. Redrawn from Nickol . Plagiorhynchus cylindraceus from an American robin Turdus migratorius, lower right, bar=1 mm. Redrawn from Schmidt and Olsen . © The American Society of Parasitologists.

Figure 2.

Male individual of Plagiorhynchus cylindraceus, a common acanthocephalan of American robins T. migratorius. P, proboscis; PR, proboscis receptacle; PRM, proboscis retractor muscle; L, lemnisci; T, testes; CG, cement glands; SP, Saefftigen's pouch; CB, copulatory bursa. Bar=1 mm.

Figure 3.

Posterior end of Centrorhynchus microcephalus, from a groove‐billed ani Crotophaga sulcirostris showing the female reproductive system. UB, uterine bell; BA, bell (selector) apparatus; U, uterus; S, sphincter; V, vagina; GO, genital opening. Bar=1 mm. After Richardson et al. . © Helminthological Society of Washington.

Figure 4.

Infective egg (shelled acanthor) of M. moniliformis from a rat. Length approximately 100 μm. Photomicrograph by JR Georgi.

Figure 5.

Acanthor of M. moniliformis. Length approximately 250 μm. Photomicrograph by RHF Holt.

Figure 6.

Life cycle of O. tortuosa, an acanthocephalan of the Virginia opossum D. virginiana. Drawing by LM Duclos.

Figure 7.

Life cycle of Lueheia inscripta, an acanthocephalan that utilises passerine birds as definitive host and cockroaches as normal intermediate hosts. Reptiles may play the role of paratenic hosts. Drawing by LM Duclos.



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Further Reading

Crompton DWT and Nickol BB (1985) Biology of the Acanthocephala. Cambridge: Cambridge University Press.

Hyman LH (1951) The Invertebrates: Vol 3. Acanthocephala, Aschelminthes, and Entoprocta: The Pseudocoelomate Bilateria. New York: McGraw‐Hill Book Co.

Pechenik JA (2005) Biology of the Invertebrates, 5th edn. Boston: McGraw Hill.

Petrochenko VI (1956) Acanthocephala of Domestic and Wild Animals. Moscow: Academy of Sciences of the USSR. (English translation (1971), Jerusalem: Israel Program for Scientific Translation).

Roberts LS and Janovy J Jr (2009) Gerald D. Schmidt and Larry S. Roberts’ Foundations of Parasitology, 8th edn. Boston: McGraw Hill.

Van Cleave HJ (1953) Acanthocephala of North American Mammals. Urbana, Illinois: University of Illinois Press.

Yamaguti S (1963) Systema Helminthum: Vol. V, Acanthocephala. New York: Interscience Publishers.

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Richardson, DJ(Mar 2013) Acanthocephala. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0001595.pub2]