Gymnophalloides heardi n. sp. differs from Gymnophalloides tokiensis Fujita, 1925 and Gymnophalloides seoi Lee et al., 1993 in the smaller body size, presence of a single, lobed vitellarium, and elongate seminal vesicle. In contrast with other gymnophallid digeneans that utilize avian and bivalve hosts, G. heardi is the first species to be reported from a rodent Oryzomys palustris (Harlan); its second intermediate host is a pulmonate gastropod, Melampus bidentatus (L.). Three gymnophallid species were found in the willet Catotrophorus semipalmatus. Parvatrema bushi n. sp. differs from Parvatrema borinquenae Cable, 1953 in the sucker ratios, arrangement of the bean-shaped vitellarium overlapping the ventral sucker, and the shallow genital atrium. Paragymnophallus kinsellai n. sp. differs from Paragymnophallus odhneri Ching, 1973 in the smaller body size, smaller sucker ratio, sharp spines, and highly lobed vitellarium. The third species found in willets was P. borinquenae; its metacercaria was found in a new gastropod host Cerithidea scalariformis (Say). The metacercariae, cercariae, and sporocysts of Parvatrema polymesoda n. sp. were found in the digestive gland of the bivalve Polymesoda maritima. The new species differs from both P. bushi and P. borinquenae in the small, bilobed vitellarium, presence of numerous sensory papillae around the oral sucker, a crenulated ventral sucker, and relatively prominent lateral papillae.