Type host: Ambystoma tigrinum (Green, 1825), Tiger salamander.

Other hosts: Ambystoma mavortium Baird, 1850, Barred tiger salamander; Ambystoma texanum (Matthes, 1855). Smallmouth salamander.

Type locality: NORTH AMERICA: U.S.A.: Iowa, Dickinson County.

Geographic distribution: NORTH AMERICA: U.S.A.: Colorado, Indiana, Iowa, Nebraska, New Mexico, Texas.

Description of oocyst: Oocyst shape: ellipsoidal; number of walls: 1; wall thickness: not given; wall characteristics: smooth, colorless to pale yellow; L x W: 31.2 x 17.7 (24.5-36 x 15-20); L/W ratio: not given; M: absent; OR: present; OR characteristics: spheroidal to subspheroidal body consisting of a hyaline sphere surrounded by small refractile granules, 12.7 x 11.4; PG: absent. Distinctive features of oocyst: large size, ellipsoidal shape, and large OR surrounded by a hyaline sphere with small refractile granules.

Description of sporocysts and sporozoite: Sporocyst shape: lanceolate; L x W: 21.9 x 5.1 (17-24 x 4-6); L/W ratio: not given; SB: present; SSB: absent; PSB: absent; SR: present; SR characteristics: scattered refractile granules, sometimes aggregated into 2 groups; SZ: elongate, almost as long and wide as sporocyst and arranged in sporocyst in a variety of twisted and parallel positions; SZ have 2 RB, one near posterior end and the other above it near the middle of SZ. Distinctive features of sporocysts: lanceolate shape with a SB at slightly pointed end.

Prevalence: At least 13 of 56 (23%) A. tigrinum from Iowa between 1951-1954 (Saxe, 1955); 1 of 1 (100%) A. tigrinum from Indiana (Bolek 2000); 17 of 17 (100%) A. mavortium from Colorado (5) and New Mexico (12) (Duszynski et al. 1972); A. mavortium from Nebraska not given (Bolek et al. 2003); and 11 of 51 (22%) A. texanum from Texas (McAllister & Upton 1987a; Upton et al. 1993). Saxe (1955) indicated that oocysts were noted in 1 of 8 Desmognathus quadramaculatus and in 1 of 2 D. monticola obtained from commercial sources, but never identified these oocysts to species.

Sporulation: Exogenous, 25-48 h; in one populatin, 80% sporulated within 48 h, while in a second population 96% sporulated in 25 h (Saxe, 1955).

Prepatent and patent periods: Unknown.

Site of infection: In the cytoplasm of epithelial cells of the small intestine from 2-10 cm above the rectum (Saxe, 1955).

Endogenous development: Saxe (1955) said he saw merozoites, macro- and microgametocytes in the cytoplasm of epithelial cells in stained sections of the lower small intestine from 3 larval A. tigrinum.

Materials deposited: Photosyntypes of sporulated oocysts are deposited in the USNPC (No. 87478).

Remarks: Oocysts from A. mavortiium from Colorado and New Mexico (Duszynski et al. 1972) and from A. tigrinum from Indiana (Bolek 2000) closely resembled those described from Iowa by Saxe (1955): oocysts from Colorado and New Mexico, 29.8 x 17.3 (24–38 x 15–25); oocysts from Indiana, 27 x 16.5 (27–28 x 15–17) vs. oocysts from Iowa, 31.2 x 17.7 (24.5–36 x 15–20); sporocysts from Colorado and New Mexico, 22.6 x 5.4 (16–27 x 5–7); sporocysts from Indiana, 15.4 x 5.1 (15–16 x 5–7) vs. sporocysts from Iowa, 21.9 x 5.7 (17–24.5 x 4–6). There were only 2 discrepancies between the 3 accounts: a) the size and composition of the OR: numerous scattered granules vs. a large hyaline structure surrounded by scattered granules; and b) Saxe (1955) did not mention the presence of a SB, while Duszynski et al. (1972) documented photographically that a SB was present. Saxe (1955) also said that the oocysts he saw may increase in size with time.