Aquatic Parasite Observatory

Ribeiroia ondatrae (Beaver, 1939)

    • Species Name: Ribeiroia ondatrae (Beaver, 1939)
    • Synonyms: Psilostomum ondatrae (Price, 1931); Cercaria thomasi (McMullen, 1938); Ribeiroia thomasi (McMullen, 1938 and Beaver, 1939); Ribeiroia insignis (Travassos, 1939); Pseudopsilostoma ondatrae (Price, 1931 and Yamaguti, 1958)
    • Taxonomy: (Beaver, 1939) Animalia, Platyhelminthes, Trematoda, Echinostomida, Psilostomatidae, Ribeiroia ondatrae
    • Description: Adult stage as described by Beaver, 1939: Body linguiform, flattened dorso-ventrally at the anterior end, more truncate in the post-testicular region. Length of mature specimens 1.4-4.2 mm; greatest width at the level of esophagus in unflattened condition; width equal to one third the length. Entire surface beset with small triangular spines arranged in close alternate rows. Oral sucker subterminal, somewhat smaller than acetabulum. Ratio of the suckers changes in favor of the acetabulum as growth progresses. The respective diameters of acetabulum and oral sucker in unflattened specimens 1.4 mm in length are 0.208 mm and 0.256 mm. Acetabulum located just anterior to middle of body in smaller mature worms but at junction of the first and second thirds in the 3-4 mm class. From 10 to 17 oral ducts extend from anterior lip of oral sucker to region of pharynx. Prepharynx very short; pharynx oval, well developed; length equal to one-half the diameter of acetabulum. Esophagus short and with large esophageal diverticula on either side extending antero-laterally to the sides of pharynx. Intestinal ceca regular, extending to the posterior end of body. Excretory pore terminal; bladder truncate, bounded by posterior testis and intestinal ceaca. Bladder bifurcates at its anterior end to receive large excretory trunks which lie on either side between the ceca and reproductive organs, and extend forward to the sides of acetabulum. Testes tandem, cubiform to elongate transversely, located in the middle third of the posterior half of the body in worms not too much flattened. Their natural dimensions are slightly less than those of the acetabulum but due to relative lack of rigidity of the hind body, the pressure causes remarkable alteration in the proportions of its contents. The testes may be enlarged in the frontal plane 3 or 4 times their normal dimensions. This is especially true of worms that have died in the gut. Cirrus pouch round, oval, pyriform, or truncate; usually located dorsal to acetabulum but may be slipped towards either side or entirely anterior to it; position in living worms shifts considerably with the different attitudes of the body but tends to remain more to the right side, and more towards the anterior slope of the acetabulum. It may reach the posterior border of the acetabulum, however. Cirrus sac nearly filled with seminal vesicle; cirrus simple, slender, and very long; prostate gland poorly developed. Genital pore located between acetabulum and bifuraction of gut. Ovary half way between dorsal and ventral surfaces, anterior to testes and to left of median line of the body; circular to oval in outline; greatest diameter 90 μ in a 1.4 mm specimen and 215 μ in a slightly flattened specimen 3.8 mm long. Oviduct leads posterodorsally to the oӧtype which is surrounded by a well developed shell gland. Yolk ducts pass under intestinal ceca, turn abruptly dorsally and enter a woluminous yolk reservoir dorsal and posterior to shell gland. Seminal receptacle absent. Laurer’s canal long, coiled irregularly. Posterior portion of uterus mostly ventral to female reproductive complex and well filled with masses of spermatozoa, forming a receptaculum seminis uterinum. Loops of uterus few, mostly transverse, and intercecal. Metraterm on left side of cirrus sac, enters a shallow non-muscular genital sinus. Vitelline follicles large and closely distributed, forming a rather compact field of either side from level of pharynx to posterior end of body. The two sides are joined by a wide isthmus at the anterior end, and they converge at the posterior end to form a single post-testicular field ventral to the excretory bladder. Eggs regular in outline, oval, 80 μ to 90 μ long by 45 μ to 50μ wide; operculum 15 μ to 18 μ in diameter; color pale brown.
    • Life Cycle: The life cycle of Ribeiroia ondatrae is indirect and utilizes three hosts. The first intermediate host is a Helisoma snail, which is infected by miracidia that hatch from eggs. The miracidia develop into rediae which eventually produce cercariae. The cercariae swim through the water and encyst on the limb buds of tadpoles. Upon metamorphosis, the tadpoles often exhibit severe malformations which leaves them vulnerable to predation by the definitive host. The definitive host is typically birds. In the bird proventriculus, the parasites mature into gravid adults that release eggs that are passed into the environment (Johnson et al., 2004).
    • Sources: Johnson, P.T.J., Sutherland, D.R., Kinsella, J.M., and Lunde, K.B. 2004. Review of the trematode genus Ribeiroia (Psilostomidae): ecology, life history and pathogenesis with special emphasis on the amphibian malformation problem. Advances in Parasitology, Vol. 57, p. 191-253.
    • APO Parasite Records: (by Life Cycle)

Parasite Images:

Distribution Map:

  • University of Colorado Boulder