title: Effect of osmolality and selected ions on retraction of the distome body into the cercaria tail chamber of Proterometra macrostoma (Trematoda: Azygiidae).
abstract: The furcocystocercous cercariae of the digenetic trematode, Proterometra macrostoma , possess a tail chamber into which their distome body withdraws prior to emergence from their snail intermediate host. The process of distome retraction and the conditions that trigger it in this species are not clear. The objectives of the present study were (1) to describe the retraction process in P. macrostoma; (2) to assess whether osmolality affects cercarial retraction; (3) to evaluate the effect of selected ions on retraction; and (4) to compare the swimming effectiveness of naturally ( =  in vivo) retracted versus in vitro retracted cercariae. Retraction of the cercaria body into its tail chamber required only 2 min or less once initiated. The process began with the development of a chamber within the anterior end of the worm's tail. The chamber's lip advanced in a pulsating motion over the stationary distome. Retraction was completed with the constriction and fusion of the chamber lip once it passed over the anterior end of the distome, sealing the latter within the tail chamber. There was a significant difference in the proportions of cercariae with bodies retracted into tails, bodies not retracted, and bodies separated from tails in artificial pond water (APW) versus artificial snail water (ASW). A greater number of cercariae withdrew into their tail chambers in ASW (59/124; 47.6%) than in APW (21/124; 16.9%). In APW, more bodies separated from their tails (24/124; 19.4%) than in ASW (3/124; 2.4%). In both solutions (APW: 63.7%  =  79/124; ASW: 50%  =  62/124), a majority of cercariae never retracted. In APW, 76.2% of distomes retracting into their tails did so within the first 5 min compared to only 30.5% in ASW. There was no significant difference in the proportions of cercariae with bodies retracted into tails, bodies not retracted, and bodies separated from tails based on isosmotic replacement of individual ions, i.e., Na(+), K(+), Ca(++), or Mg(++), in ASW with Li(+). There was also no significant difference in the vertical swimming burst distance in cercariae whose bodies were initially retracted into their tails in vitro versus in vivo.
authors.affiliation: Department of Biology, Berea College, Berea, Kentucky 40404, USA. ron_rosen@berea.edu
authors.forename: Ronald
authors.initials: R
authors.lastname: Rosen
authors.forename: Cecilia
authors.initials: C
authors.lastname: Albers
authors.forename: Adam
authors.initials: A
authors.lastname: Chambers
authors.forename: Alaina
authors.initials: A
authors.lastname: Faust
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Fleming
authors.forename: Alisha
authors.initials: A
authors.lastname: Holmberg
authors.forename: Adam
authors.initials: A
authors.lastname: Meador
authors.forename: Kelly Njine
authors.initials: KN
authors.lastname: Mouapi
authors.forename: Krystina
authors.initials: K
authors.lastname: Sandefur
authors.forename: Lee
authors.initials: L
authors.lastname: Ware
mesh_terms: D000818:Animals; D002122:Calcium Chloride / Q000494:pharmacology; D005618:Fresh Water; D018021:Lithium Chloride / Q000494:pharmacology; D015636:Magnesium Chloride / Q000494:pharmacology; D009994:Osmolar Concentration; D011189:Potassium Chloride / Q000494:pharmacology; D012908:Snails / Q000469:parasitology*; D012965:Sodium Chloride / Q000494:pharmacology; D014200:Trematoda / Q000187:drug effects / Q000502:physiology*
chemical_list: D015636:Magnesium Chloride; D012965:Sodium Chloride; D011189:Potassium Chloride; D018021:Lithium Chloride; D002122:Calcium Chloride