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

Abstract

The objectives of this study were to describe (1) the osmotic environment and precise location of the Proterometra macrostoma redia in its snail intermediate host, (2) where retraction of the distome body into the cercarial tail occurs, and (3) the subsequent emergence path of the cercaria out of the snail. Snails, Elimia semicarinata , were collected from North Elkhorn Creek in Scott County, Kentucky and screened daily for patent infections. Live rediae were extracted from infected snails in either artificial pond water (APW) or artificial snail water (ASW) and monitored for changes in morphology and movement every hour over 5 hr at 22 C. Infected and control snails were simultaneously fixed and decalcified in Cal-Ex II, prepared for routine paraffin sectioning, and serial sections subsequently analyzed for rediae and cercariae location. Significantly (χ(2) = 42.45; 1 df; P = 0.0001) more rediae showed movement in ASW than in APW after 5 hr, suggesting a host compartment separate from the mantle cavity. Histological sections clearly showed rediae developing in close association with the snail digestive tract, within the peri-intestinal sinus of the snail, and isolated from the mantle cavity by a mantle membrane. Retraction of the distome body into the cercarial tail follows the emergence of the cercaria from the redia. Cercariae then enter the mantle cavity and emerge into fresh water through a siphon-like structure formed by the mantle collar of the snail.

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

“…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].…”

Determination and Quantification ofSchistosoma mansoniCercarial Emergence fromBiomphalaria glabrataSnails

“…One figure from that study showed a cercaria emerging from the tissues of the snail, but no attempts were made to determine the relative importance of the anterior tissues in the shedding process. More recent studies in other trematode systems (Oates and Fingerut, 2011;Rosen et al, 2013) have also described cercarial emergence from anterior tissues of snails. These studies have all agreed that cercariae can emerge from several tissues, and those involved seem to be the mantle collar, headfoot, anus, and pseudobranch.…”