Encyclopedia of Parasitology

2016 Edition
| Editors: Heinz Mehlhorn


Reference work entry
DOI: https://doi.org/10.1007/978-3-662-43978-4_2221


Subphylum of  Sarcomastigophora.

General Information

These relatively large (up to 1 mm long)  protozoa are characterized by numerous close rows of short  flagella which move metachronously. Although these flagella look like  cilia, the basic organization is quite different. Opalinids have two to numerous identical nuclei; micro- or macronuclei are always absent. Asexual reproduction occurs by longitudinal-oblique  binary fission (Figs. 1 and 2); in some species, however, additional sexual fusion stages have been reported. In general the opalinids inhabit the colon or  cloaca of amphibians, reptiles, and fish; their pathogenic effects are low; mostly they feed as commensals on intestinal fluids (by  pinocytosis). Transmission occurs mainly by oral uptake of cysts (Fig. 1).
Opalinata, Fig. 1

Life cycle of Opalina ranarum. 1 Cysts are excreted by the adult frog and orally ingested by a tadpole. 2 After hatching the young  gamont migrates to the cloaca. 3, 4 Formation of micro- and macrogametes (meiosis). 5 Fusion of the heterogametes. 6 Encystation of the  zygote and excretion via feces. 7, 8 After oral uptake of a cyst by another tadpole the trophozoite grows up in the cloaca (up to 0.5 mm). 8.1, 8.2 The small trophozoite may start division inside the tadpole, finally leading to formation and excretion of cysts (1) which give rise to new  trophozoites (28) after ingestion by another tadpole. 9 When  metamorphosis of tadpoles to frogs is completed, the trophozoites (agamonts, trophonts) grow up and form up to 2,000 nuclei. 10 During the nonbreeding season of the frog the trophozoites multiply by binary  fission, the axis of which is either longitudinal or oblique-transverse. 11, 12 During the breeding season hormones released by the frog induce rapid divisions of the trophozoites without compensatory nuclear divisions and growth. Thus the parasites (precystic forms) become successively smaller. These stages, finally having 2–12 nuclei, encyst (1), are set free with the feces of the host, and become infectious for tadpoles. CI cilia, CW cyst wall, N nucleus

Opalinata, Fig. 2

LM of a typically shaped asexual stage of Opalina ranarum from the cloaca of frogs


  • Subphylum: Opalinata
    • Class: Opalinatea

    • Order: Opalinida
      • Genus: Opalina (in frogs)

      • Genus: Protoopalina (in fish)

      • Genus: Cepedea (in several amphibia)

      • Genus: Zelleriella (in Bufo)

Life Cycle

See Figs. 1 and 2.

Copyright information

© Springer-Verlag Berlin Heidelberg 2016

Authors and Affiliations

  1. 1.Institut für Zoomorphologie, Zellbiologie und ParasitologieHeinrich-Heine-UniversitätDüsseldorfGermany