This image is of an encysted individual. These are excreted in the feces of felids, and are then passed into mammal or avian intermediate hosts. Infections are usually asymptomatic in adult humans, but the parasite can cause severe damage if transmitted through the placenta in an infected pregnant woman.
Duboscquella is an endoparasite of tintinnid ciliates. The ciliate ingests the dinoflagellate, which grows within the host's body. The image here is of dinospores (the propagative form) emerging from the empty, wine-goblet shaped lorica of the tintinnid. Read more about these organisms.
Elphidium excavatum and othr members of its genus are extremely common in salt marshes and other brackish-water environments. Foraminiferans are famous for the often elaborate shells that they build, which assist in feeding and many other life processes. This live individual is tinted a brilliant orange by the algae it feeds on. Read more about forams and other Granuloreticulosea.
An empty frustule (glassy external skeleton) of the marine centric diatom Coscinodiscus. Read more.
Heteroloboseans are amoeboid protists whose pseudopods form as sudden bulges (so-called "eruptive" pseudopodia). Vahlkampfiid heteroloboseans often form cysts, as seen here.
Organisms in this group often create mineralized structures called coccoliths, which are the wheel-like objects covering the cell shown here. This particular species also exists in a motile form, which has no coccoliths but is covered with a single layer of organic scales.
The image is an SEM of the anterior end of the cell. Pellicle strips which form the cell covering invaginate around the flagellar opening.
Mating Tetrahymena thermophila cells labeled with antisera to beta tubulin (blue), TCBP-25 (pink) and sytox as a nuclear stain (yellow). These cells have just completed second meiosis.