Figure 1.
The various stages of the schistosome life cycle are depicted using fluorescence (sporocysts and cercariae in snail host labeled with DAPI (green), phalloidin (magenta), and peanut agglutinin (orange)), bright-field (egg), or scanning electron micrographs (remaining stages). Images are not shown to scale.
Figure 2.
Similarities between schistosomes and planarians.
(A) Schistosomes (left column) and planarians (right column) possess common cell types and organ systems. Top row, (left) scanning electron micrograph of male and female S. mansoni and (right) dark-field image of S. mediterranea. Second row, eggs. Both organisms lay ectolecithal egg capsules with a polyphenolic shell. Only a subset of derived flatworm species (called neoophora) lay this unique type of egg. Third row, glands associated with the egg-laying apparatus. These glands (Mehlis' gland in schistosomes and cement gland in planarians) labeled with the lectin, peanut agglutinin (green) [11], [37]. Although these glands are found in both free-living and parasitic flatworms, their function is unclear. Fourth row, confocal images of protonephridia labeled with (left) anti-acetylated tubulin (green)/wheat germ agglutinin (magenta) and (right) anti-acetylated tubulin (green). Protonephridia are found in most platyhelminths and play essential roles in controlling water balance [38], [39]. Since schistosomes conform to the osmolarity of their host, it is also likely this organ system has additional functions (e.g., excreting waste). Fifth row, labeling with thymidine analogs to detect neoblasts (orange nuclei). All other nuclei are magenta. (B) Simplified phylogeny of the Platyhelminthes. Images depict representative genera from each group. Images from each group are as follows: Macrostomida (Macrostomum sp.), Polycladida (Pseudobiceros hancockanus, credit: J. Petersen), Tricladida (Schmidtea mediterranea), Monogenea (Diplozoon sp., credit: D. Thenet, R. Kirk, and P. Olson), Cestoda (Hymenolepis sp., credit: P. Olson), Trematoda (Schistosoma mansoni).