Myxobolus mississippiensis n. sp. (Myxosporea) from Gills of Lepomis macrochirus in Mississippi

Myxobolus mississippiensis n. sp. is described from gill lamellae of the bluegill (Lepomis macrochirus) inhabiting the Pascagoula River System, Mississippi. Fresh spores measure 16.4-18.7 μm long, 3.9-6.2 μm wide, and 4.7-6.2 μm thick. Spore width to length ratio is 1:3.2. Polar capsules are 5.5-7.8 μm long and 1.5-2.3 μm wide, with 9-10 filament coils that when extruded measure 42.1 ± 4.2 μm. This parasite is unique among known species of Myxobolus,/i> in having spores that are lenticular in frontal view.

Heligmosomoides johnsoni sp. nov. (Nematoda: Heligmosomatidae) from the Heather Vole, Phenacomys intermedius Merriam

Heligmosomoides johnsoni sp. noy. is described from the cecum of the heather vole, Phenacomys intermedius Merriam, from the Olympic Mountains, Washington. The absence of longitudinal cuticular ridges dorsally separates H. johnsoni from species of Heligmosomoides other than H. hudsoni (Cameron, 1937), which occurs in varying lemmings, Dicrostonyx spp., and from which H. johnsoni is distinguished by its longer spicules, form of the dorsal ray, and other characters. Both Phenacomys and Dicrostonyx have a specialized cecum, with long villi around which the nematodes are found tightly coiled. The zoogeography of heligmosomid nematodes in Phenacomys is briefly discussed. French abstract: On décrit Heligmosomoides johnsoni sp. nov. parasite du caecum du rongeur néarctique, Phenacomys intermedius Merriam, des Montagnes Olympiques de Washington. L'absence de crêtes cuticulaires sur la face dorsaIe sépare H. johnsoni des autres Heligmosomoides à I'exception d'H. hudsoni (Cameron, 1937) qui se trouve chez Dicrostonyx spp., et duquel H. johnsoni se distingue par ses spicules plus longs, par la forme différente de la côte dorsale et par d'autres caractères. Phenacomys et Dicrostonyx ont un caecum spécialisé, muni de villosités allongées, autour desquelles les nématodes s'enroulent étroitement. La zoogéographie des nematodes héligmosomes chez Phenacomys est discutée.