Redescription and life-cycle of : Plagiorchiidae) a parasite of Australian freshwater turtlesSigmapera cincta: Plagiorchiidae) a parasite of Australian freshwater turtles Nicoll, 1918 (Digenea: Plagiorchiidae) a parasite of Australian freshwater turtles

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Abstract

Sigmapera cincta Nicoll, 1918 is redescribed and its life-cycle outlined. Important taxonomic features omitted from the original description, or incorrectly described, include a heavily spined cirrus, bipartite seminal vesicle, ventral sucker larger than oral sucker, oesophagus much longer than prepharynx, tegumental spines extending almost to posterior end, primary collecting ducts arising ventro-laterally from the bladder arms, flame-cell formula 2{(2 + 2 + 2) + (2 + 2 + 2)} and dorsal genital protuberance present with Laurer's canal opening at its posterior edge. The life-cycle is three-host, aquatic and was established experimentally. Glyptophysa gibbosa served as both a first and second intermediate host in the laboratory. The snails Austropeplea lessoni and Glyptophysa sp. and tadpoles of Limnodynastes peronii, Adelotus brevis, Litoria caerulea and Bufo marinus also served as natural and experimental second intermediate hosts. Adult worms were parasitic in the small intestine of the turtles Chelodina longicollis, C. expansa, Emydura macquarrii and Elseya latisternum. Eggs were unembryonated when laid, embryonated in water in 8 to 14 days at 24–28 °C, and did not hatch until eaten by Glyptophysa gibbosa. Eggs hatched in the stomach and first 2/5 of the intestine of G. gibbosa. Miracidia penetrated the intestinal epithelium in the first 2/5 of the gut. Xiphidiocercariae first emerged from G. gibbosa after 32 days at 24–28 °C. Cercariae attached to snails, tadpoles and fish and penetrated through the skin. Metacercarial cysts were distributed randomly throughout the tissues of experimentally infected snails and tadpoles. Precocious encystment of metacercariae within the sporocysts in the first intermediate host was common in naturally infected snails and occurred without exception in experimentally infected G. gibbosa. Based on the presence of a true xiphidiocercaria and a Y-shaped excretory bladder, Sigmapera is removed from the Omphalometridae and included in the Plagiorchiidae.

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