Type host: Ambystoma opacum IGravenhorst, 1807), Marbled salamander.

Other hosts: None reported to date.

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

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

Description of oocyst: Oocyst shape: spheroidal to slightly subspheroidal; number of walls: 2; wall thickness: ~1.0; wall characteristics: outer layer smooth, ~1/2 of total thickness ; L x W: 29.4 x 23.8 (27-32 x 25-31); L/W ratio: 1.0 (1.0-1.1); M: absent; OR: absent; PG: absent. Distinctive features of oocyst: large size with 2 walls layers of equal thickness.

Description of sporocysts and sporozoite: Sporocyst shape: ellipsoidal when viewed from one side, but kidney-bean shaped when viewed from the other side; L x W: 17.4 x 9.1 (16-21 x 8-11); L/W ratio: 1.7 (1.6-2.3); SB: absent; SSB: absent; PSB: absent; SR: present; SR characteristics: composed of 1-2 small clusters of coarse granules; SZ: 20-24 x 4-5, with large posterior RB 7.7 x 4.2 (5.5-9.5 x 4-5) and centrally located N. Distinctive features of sporocysts: each sporocyst is loosely enclosed in a secondary sporocyst wall, with ends of the secondary wall connected by a frail, membrane-like material; 1–3 homogeneous globules are present between primary and secondary sporocyst walls with other homogeneous globular material flattened against inner portion of secondary wall.

Prevalence: 1 of 5 (20%).

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.

Endogenous development: Unknown.

Materials deposited: Photosyntypes of sporulated oocysts are deposited in the USNPC (No. 83259). The symbiotype host (sensu Frey et al. 1992) was an adult male, 50 mm snout-vent length, collected 20 March 1992, and is deposited in the ASUMZ (Cat. No. 18276).

Remarks: Oocysts of E. opacum are unique among the coccidia because of the double-walled structure of the sporocysts; even the kidney-bean shape itself is rare. Rankin (1937) found unsporulated oocysts in A. opacum that were 17 x 12, measurements identical to those reported for the macrogametes/unsporulated oocysts of E. ranarum (Laveran & Mesnil 1902a), a parasite of ranids in Europe. Likewise, Walton (1942) mentioned an eimerian from an unspecified Ambystoma species, which Saxe (1955) later reported through personal communication with Walton as also being from A. opacum, but did not identify it.