Synonyms: Isospora sp. of McAllister and Upton, 1987.

Type host: Gastrophryne olivacea (Hallowell, 1856), Great Plains narrowmouth toad.

Other hosts: None reported to date.

Type locality: NORTH AMERICA: Texas, Somervell County.

Geographic distribution: NORTH AMERICA: Texas.

Description of oocyst: Oocyst shape: spheroidal; number of walls: 1; wall thickness: ~0.8; wall characteristics: smooth, thin, ruptures 1-3 d after sporulation, releasing sporocysts; L x W: 18.5 (17-21); L/W ratio: not given; M: absent; OR: absent; PG: absent. Distinctive features of oocyst: thin wall that ruptures after sporulation, releasing sporocysts.

Description of sporocysts and sporozoite: Sporocyst shape: ovoidal; L x W: 12.7 x 10.9 (11-14 x 10-12); L/W ratio: 1.2 (1.1-1.3); SB: absent; SSB: absent; PSB: absent; SR: present; SR characteristics: coarsely granular, spheroidal or ovoidal, 7.9 x 6.9 (5-11 x 5-10); SZ: elongate, 12.6 x 3.4 (12-14 x 3-4) in situ, with 2 SZ in one direction and 2 in the opposite direction, each with 2 RBs; anterior RB is spheroidal, 2.3 (1.2-2.4) and posterior RB is spheroidal to ovoidal, 3.0 x 2.3 (2-4 x 2-3); N located between the 2 RBs. Distinctive features of sporocysts: sometimes slight thickenings may be seen at opposite ends and at sides of sporocysts, suggesting the presence of sutures.

Prevalence: 14 of 95 (15%). The prevalence in adult frogs, given by month, appears to fluctuate seasonally: February, 0 of 16 (0%); March 4 of 9 (44%); April 4 of 16 (25%); May 3 of 19 (16%); June 1 of 21 (5%); July 0 of 2 (0%); September 2 of 7 (29%); and October 0 of 5 (0%).

Sporulation: Exogenous. Oocysts recovered from feces were unsporulated, partially sporulated, or rarely, fully sporulated.

Prepatent and patent periods: Unknown.

Site of infection: Unknown, but see Remarks.

Endogenous development: Unknown.

Materials deposited: None.

Remarks: This species most closely resembles I. neos reported from R. arvalis in the former USSR (Yakimoff & Gousseff 1936b); however, its oocysts are smaller than those of I. neos and its sporocysts have a large, highly distinctive SR, which those of I. neos lack. Kazubski and Grabda-Kazubska (1973)reported an isosporan from R. arvalis in Poland that is slightly larger than I. fragosum and has a SR. Even though Yakimoff and Gousseff (1936b) stated specifically that I. neos lacked a SR, Kazubski and Grabda-Kazubska (1973) identified the form they found as I. neos because, according to Kheysin (1967, as cited in Kazubski and Grabda-Kazubska, 1973), the SR is used to provide nutrition to the SZ and, thus, may disappear with time. Upton and McAllister (1988) considered this hypothesis unlikely and suggested that the isosporan reported by Kazubski and Grabda-Kazubska (1973) may be a separate, yet undescribed, species. However, recently we were able to observe changes in the SR and OR of I. cogginsi stored at room temperature in 2.5% K2Cr2O7 solution for a period of 14 mo and determined that both the SR and OR disappeared in this species, suggesting that researchers working on new descriptions should report the time period elapsed between collection and species description of coccidians. Upton and McAllister (1988) reported the site of infection for this species as the intestine. However, the oocysts were recovered from the feces and no attempt was made to check what organs were infected with developmental stages of I. fragosum; therefore, the site of infection of this species is unknown.