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.

Proterometra epholkos sp. n. (Digenea: Azygiidae) from Terrapin Creek, Alabama, USA: Molecular characterization of life cycle, redescription of Proterometra albacauda, and updated lists of host and geographic locality records for Proterometra spp. in North America

“…[7][8][9][10][11][12][13][14] Diagnosis of adult based on light microscopy of 7 stained whole mounted specimens. Body of adult orange (live coloration), 1980-2300 (2189, 7) long, 820-1280 (1169, 7) or 1.7-2.7 (1.9, 7)× longer than wide, ventrally concave; tegument approximately 10-20 (14, 7) thick; papillae loosely studding rim of the mouth, tightly encircling the outside rim of the ventral sucker, pored, lacking sensory cilium; tegumental projections (not illustrated) distributed evenly from anterior to posterior end (Fig.…”

“…The latter three species were treated initially by Smith [15,12,21] and all of them require further taxonomic study considering the type materials and based on naturally shed cercariae as well as adults collected from infected, wild-caught fish hosts. Fundamentally problematic is that we could not locate or find reference to an extant type specimen for any species of Proterometra described from Alabama.…”

“…This makes the assessment of operational taxonomic units based on cercarial morphology alone challenging, especially given the low number of reported diagnostic characteristics. Various workers have treated morphology, behavior, and host-parasite relationships of the cercariae [13,[6][7][8][9][10][11][12]33,[66][67][68][69][70][71][72], development and morphology of the eggs [35,73] and adults [1,6,15,[21][22][23][24][25]28,33,35], and general attributes of the intra-molluscan stages, sporocyst and redia [11,14,74]. Moreover, 8 cercarial strains of P. macrostoma have been morphologically characterized from Lake Erie [13], Kentucky [8,75], Michigan [8], and Ohio [8].…”

“…6,12). Others have referred to these tail stem protuberances as "papillae" [22] or "wartose structures" [33].…”

Proterometra macrostoma(Trematoda: Azygiidae): Location of the Redia and Emergence Path from the Snail,Elimia semicarinata(Gastropoda: Pleuroceridae)

“…In addition, recent osmotic evidence supports a body compartment other than the mantle cavity as the location for P. macrostoma rediae and the site for this distome's body retraction into its cercarial tail. Rosen et al (2011) found significantly more distome bodies retracted into their cercarial tails in artificial snail water (ASW) than in artificial pond water (APW). Presumably ASW more closely approximates the osmolality of this body compartment compared to the osmolality of the mantle cavity.…”