Synonyms: Isospora sp. of McAllister, Upton, and Trauth, 1993.

Type host: Plethodon albagula Grobman, 1944, Western slimy salamander.

Other hosts: None reported to date.

Type locality: NORTH AMERICA: U.S.A.: Arkansas, Grant County, 6.4 km SW Sheridan.

Geographic distribution: NORTH AMERICA: U.S.A.: Arkansas.

Description of oocyst: Oocyst shape: spheroidal, rarely subspheroidal; number of walls: 2; wall thickness: ~1; wall characteristics: outer smooth, ~1/2 of total thickness; L x W: 22.9 x 22.8 (21-24 x 21-24); L/W ratio: 1.0 (1.0-1.0+); M: absent; OR: present; OR characteristics: a mass of small granules surrounding a central globule, all enclosed in a thin membrane, ~2.5-5 wide, but present in only 33% of the oocysts; PG: absent. Distinctive features of oocyst: unique OR that is present in only about 1/3 if the oocysts.

Description of sporocysts and sporozoite: Sporocyst shape: ovoidal, slightly pointed at one end; L x W: 16.6 x 11.1 (14.5-17.5 x 10.5-14); L/W ratio: 1.5 (1.4-1.6); SB: present as large knob at pointed end, 1.2-1.6 high x 2-2.5 wide; SSB: present; PSB: absent; SR: present; SR characteristics: composed of numerous coarse globules scattered among SZ; SZ: elongate sausage-shaped, 13.6 x 2.7 (12-14.5 x 2.5-3) each with 2 RB; anterior RB subspheroidal to ellipsoidal, 2.7 x 2.5 (2.5-3 x 2-3) and posterior RB smaller, spheroidal to subspheroidal, 2.3 x 2.2 (2-3 x 2-2.5); N located between refractile bodies. Distinctive features of sporocysts: large, distinct SB and SSB.

Prevalence: 8 of 46 (17%).

Sporulation: Exogenous. All oocysts were passed unsporulated and became fully sporulated within 1 wk at 23ºC.

Prepatent and patent periods: Unknown.

Site of infection: Unknown. Oocysts recovered from feces and intestinal contents.

Endogenous development: Unknown.

Materials deposited: Photosyntypes deposited in the USNPC (No. 83260). Symbiotype host (sensu Frey et al. 1992) a juvenile male, 25 mm snout-vent length, collected 20 March, 1992, deposited in the ASUMZ (Cat. No. 18277).

Remarks: The only other isosporan described from caudate amphibians is I. jeffersonianum from the blue-spotted salamander A. laterale (=A. jeffersonianum) from Minnesota. The latter possesses a knob or thickening in the oocyst wall that I. hightoni lacks and the sporocysts of I. jeffersonianum are more elongate than those of I. hightoni.