Pentastomids comprise an ancient taxon of about 110 species of vermiform endoparasites which attain maturity in the respiratory tracts of terrestrial tetrapods. About 85% of species inhabit the lungs of reptiles. Life cycles usually involve an intermediate host, although a few are direct. An unprecedented fossil record, dating from the late Cambrian, indicates a long association with vertebrates.

Keywords: pentastomida; life cycles; lung parasites; reptile hosts; fossil parasites

Figure 1.

Living pentastomids in situ or in vitro. (a) A female Armillifer armillatus within the lung of a freshly dissected African rock python (Python sebae) (photograph courtesy of Peter Boreham). (b) Developing eighth‐stage, lung‐dwelling instars of Armillifer armillatus from an in vitro culture. Individuals have bulbous heads and tapered caudal extremities; the raised annuli consist predominantly of large glandular cells. The bunched annuli on the specimen furthest left represent a wave of peristalsis moving forwards towards the head during active locomotion (same scale as (c)). (c) Developing eighth‐ and ninth‐stage instars of Porocephalus crotali from an in vitro culture system. In this species both extremities are bulbous but the head is the more prominent. These parasites would normally reside in the lung of a rattlesnake. White scale bar, 1 cm.

Figure 2.

Schematic representations of the male and female reproductive systems of cephalobaenid and porocephalid pentastomids (not to scale). (a) A mature female cephalobaenid showing the positions of the ovary, oviduct and spermatheca relative to the saccate uterus. The latter fills most of the available haemocoel and eggs are discharged through an anterior genital pore. (b) A female porocephalid with an elongate, tubular uterus leading to a posterior genital pore. (c) and (d) represent the anterior regions of (a) and (b) at the time of copulation when these females are immature and the uterus undeveloped. At this stage, the paired spermatheca are relatively accessible through the genital pore. (e) The paired tubular penises and associated chitinous dilators of a male cephalobaenid. During copulation, the dilators may be thrust into the female and serve to guide the amuscular thread‐like penises directly to the spermathecal ducts. (f) The same in a male porocephalid. The chitinous, amuscular penis threads are long and coiled, reflecting the greater distance between the female gonopore and the spermatheca. The dilators introduce the ornamented tip into the vagina, but their extension depends upon peristaltic muscle action of the vagina/uterus. In both orders of males, the gonopore is anterior in position, being located just behind the mouth in the midventral line. C, cirrus; D, dilator; gp, genital pore; I, intestine; O, ovary; OV, oviduct; S, spermatheca; U, uterus; vd, vas deferens. (Reproduced, with permission, from Riley, 1986.)


Further Reading

Fain A (1961) Les pentastomides de l’Afrique Centrale. Annales de Musée Royale de l’Afrique Centrale 92: 1–115.

Haugerud RE (1989) Evolution in the Pentastomida. Parasitology Today 5: 126–132.

Mehlhorn H (1988) Parasitology in Focus. Heidelberg, Germany: Springer‐Verlag.

Riley J (1983) Recent advances in our understanding of pentastomid reproductive biology. Parasitology 86: 59–83.

Riley J (1986) The biology of the Pentastomida. Advances in Parasitology 25: 46–128.

Riley J (1992) Pentastomids and the immune response. Parasitology Today 8: 133–137.

Riley J (1992) Pentastomida. Reproductive Biology of Invertebrates 5: 401–411.

Riley J (1994) Pentastomida. Reproductive Biology of Invertebrates 6: 293–308.

Self JT (1969) Biological relationship of the Pentastomida; a bibliography on the Pentastomida. Experimental Parasitology 24: 63–119.

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How to Cite close
Riley, John(Apr 2001) Pentastomida. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1038/npg.els.0001609]