Histochemical characteristics of the metacercarial cyst wall of Gynaecotyla adunca

The cyst wall of the metacercaria of Gynaecotyla adunca (Microphallidae: Digenea) was subjected to comprehensive histochemical analysis. At the light microscope level, a uniformly thick, bipartite cyst wall, probably wholly of parasite origin, was evident. Structural modification of the cyst wall to provide an escape aperture was not apparent. The thicker, inner layer was comprised of phospholipid and glyco- and/or mucoproteins, possibly similar in structure to collagen. The outer layer was highly proteinaceous and contained additional amounts of acidic and neutral mucosubstances. The results are discussed in the context of previous observations regarding the excystment requirements of this microphallid species.

Evidence for the presence of quinone methide isomerase in the metacercarial cyst of Microphallus sp. (Trematoda: Microphallidae)

The white colour of the cyst wall of the metacercaria of Microphallus sp., even in the presence of dihydroxy phenol and phenoloxidase, is due to proteins generated through a possible quinone methide interaction. The quinone methide isomerase converts the phenoloxidase mediated quinone into β-hydroxy catechol. Formation of catechol from quinone by cyst extracts was observed spectrophotometrically and chromatographically. This enzyme is involved in detoxification of excess quinone and β-sclerotization of the cyst wall.

An in vitro study of the forcible ejection of the metacercaria of the strigeid digenean Apatemon (Australapatemon) minor Yamaguti, 1933 by rapid inward expansion of the cyst wall

ABSTRACTIt has been established that the wall of the metacercarial cyst of the strigeid digenean Apatemon (Australapatemon) minor from the leech Erpobdella octoculata shares with Apatemon (Apatemon) gracilis the remarkable ability to expel the metacercaria forcibly from the cyst, an event which presumably occurs when the cysts are eaten by the bird definitive host. When cysts of A. minor are treated in vitro with a solution containing a mixture of bile salts and trypsin following pretreatment with acid pepsin, the metacercaria is expelled in an explosive manner through a canal at the narrow end of the pear-shaped cyst. This expulsion is produced by a sudden and substantial inward expansion of the birefringent wall, as a consequence of which the cyst lumen is virtually eliminated. Expulsion of the metacercaria in this explosive manner also occurs when similarly pretreated cysts are exposed to either bile salts alone or to trypsin, but cysts treated with the latter take longer to respond. When the cyst wall is perforated with a needle, inward expansion of the wall occurs and the metacercaria is forcibly ejected through the perforation. A variety of other pretreatments and treatments was tested but pepsin appears to be the most effective “primer”, apparently producing localized changes which permit the exit of the metacercaria. These observations are discussed in relation to the mechanism of expulsion.