Synonyms: Acystis parasitica (Labbe, 1894), pro parte; Caryophagus ranarum Labbe, 1899; Coccidium ranarum (Labbe, 1894) Laveran and Mesnil, 1902; Karyophagus ranarum Labbe, 1894.

Type host: Pelophylax esculenta (L., 1758), Pool frog.

Other hosts: Rana temporaria L., 1758, Grass frog.

Type locality: EUROPE: France.

Geographic distribution: EUROPE: France.

Description of oocyst: Oocyst shape: ellipsoidal to ovoidal; number of walls: 1; wall thickness: "thin"; wall characteristics: smooth; L x W: 18-20 x 12-16; L/W ratio: not given; M: present (line drawing in Laveran and Mesnil, 1902); OR: absent; PG: absent. Distinctive features of oocyst: presence of a small M.

Description of sporocysts and sporozoite: Sporocyst shape: spindle-shaped with both ends tapering to a point; L x W: 7 x 4; L/W ratio: 1.8; SB: absent; SSB: absent; PSB: absent; SR: present; SR characteristics: scattered ovoid globules; SZ: about the same length as the sporocysts (line drawing). Distinctive features of sporocysts: very small and spindle-shaped.

Prevalence: Unknown.

Sporulation: Exogenous, but oocysts passed in feces in an advance state of sporulation.

Prepatent and patent periods: Unknown.

Site of infection: Development is exclusively within the N of small intestinal epithelial cells.

Endogenous development: Meronts contain 25–30 small merozoites, ~5–6 long, arranged in irregular rows. Microgametes are also small, ~3 long. Ellipsoidal macrogametes are filled with large granules and are ~17 x 12 when discharged into the lumen of the small intestine; at that time they have a distinct M, through which Laveran and Mesnil (1902a) believed the microgametes entered.

Pathology: Atrophy of the infected host cell N.

Materials deposited: None.

Remarks: The history of the discovery and naming of this coccidium is convoluted and confusing and is best summarized by Dobell (1909) who wrote that Labbé (1894b) mentioned that he found a parasite, like that occurring in newts, in the N of the intestinal epithelium of Rana temporaria. Without giving any further description he bestowed the name Karyophagus ranarum n. sp. upon it. But on the very next pager he said that he believed that this parasite is identical with Karyophagus salamandrae Steinhaus, and Cytophagus salamandrae Steinhaus, and he proposed to call them all Acystis parasitica! Later, Labbé (1899) retained the name Caryophagus ranarum Labbé for the intestinal coccidium of the frog, but gave the host as Rana esculenta (=Pelophylax esculenta), and gave no further description of it. It is obviously useless to attach much importance to these names, and impossible to identify the animal(s). Walton (1941, 1961) erroneously reported 2 Ambystoma spp. as hosts for this coccidium.