thumb|[[Apicomplexan life cycle|Tachyzoites of Toxoplasma gondii, transmission electron microscopy. Rhoptries: ro (click to enlarge)]]
A rhoptry is a specialized secretory organelle. They are club-shaped organelles connected by thin necks to the extreme apical pole of the parasite. These organelles, like micronemes, are characteristic of the motile stages of Apicomplexa protozoans. They can vary in number and shape and contain numerous enzymes that are released during the process of host penetration. The proteins they contain are important in the interaction between the host and the parasite, including the formation of the parasitophorous vacuole (PV).
Characteristics
Rhoptries are one of the three characteristic secretory organelles present in all Apicomplexa along with micronemes and dense granules. The name rhoptry indicates its shape as it comes from the Greek word for "club-shaped." These large membrane-bound organelles are electron-dense and highly acidic
There is a variation in the number of rhoptries present in different species and during different developmental stages. For example, the tachyzoite stage of Toxoplasma gondii, which is found during the acute phase of toxoplasmosis, has 10 to 12 rhoptries, while the bradyzoite stage observed during the chronic phase of the infection has one to three rhoptries. Meanwhile, Cryptosporidium sporozoites only have a single rhoptry. and contains the rhoptry neck proteins (RONs),