Type host: Sorex palustris Richardson, 1828, Northern water shrew.

Other hosts: Sorex pacificus Coues, 1877, Pacific shrew; Sorex trowbridgii Baird, 1858, Trowbridge shrew; Sorex unguiculatus Dobson, 1890, Long-clawed shrew; Sorex vagrans Baird, 1858, Vagrant shrew.

Type locality: NORTH AMERICA: USA, New Mexico, Santa Fe County, 8 km N, 12.9 km E, Santa Fe.

Geographic distribution: ASIA: Japan, Hokkaido; NORTH AMERICA: USA, California, New Mexico, Oregon, Washington.

Description of oocyst: Oocyst shape: subspheroid; number of walls: 2; wall thickness: <1.0; wall characteristics: outer, generally with a few small bumps, irregularly spaced, ~1/2 of total thickness, and with a striated appearance in optical cross section; L x W: 17.6 x 16.7 (16-19 x 16-18); L/W ratio: 1.1 (1.0-1.2); M: absent; OR: absent; PG: usually 1, but sometimes (30%) as 2-4 fragments of irregular size and shape. Distinctive features of oocyst: subspheroid shape with striated outer wall.

Description of sporocysts and sporozoites: Sporocyst shape: ovoid; L x W: 12.8 x 8.3 (12-14 x 8-10); L/W ratio: 1.6 (1.23-1.8); SB: present; SSB: present, almost spheroid, about the same width as SB; PSB: absent; SR: present; SR characteristics: many small granules; SP: probably have 1 large RB at rounded end, which was not reported in the original description, but is seen in the line drawing. Distinctive features of sporocyst: spheroid SSB.

Prevalence: 2/12 (8%) S. pacificus; 3/41 (7%) S. palustris; 3/105 (3%) S. trowbridgii; 1/48 (2%) S. unguiculatus; 1/112 (<1%) S. vagrans.

Sporulation: Exogenous. Oocysts sporulated in 7-10 days in 2.5% aqueous (w/v) potassium dichromate solution at ~23 C.

Prepatent and patent periods: Unknown.

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

Materials deposited: Skin, skull, skeleton and tissues of the symbiotype host are preserved in the Mammal Division of the Museum of SW Biology, UNM: MSB No. 41122 (NK 1002, male), R.A. Hoyt #098, 6 July 1979. Photosyntypes in the USNPC No. 86357.

Remarks: Oocysts and sporocysts of this species are very similar to those of I. brevicauda, but differ in 2 ways: 1) oocyst length, oocyst width, sporocyst length, sporocyst width and oocyst L/W ratio of I. brevicauda from Blarina sp. were highly significantly smaller (P<0.0001, Student's t-distribution) than those of I. palustris from Sorex spp. even though the respective means and ranges are similar; and 2) the width of the SSB is about the same as the SB in I. palustris, whereas it is 2 times wider than the SB in I. brevicauda; also, the shape of the SSB is different between the 2 species.

References: Hertel and Duszynski (1987).