Mermithids (Nematoda: Mermithidae) of biting midges (Diptera: Ceratopogonidae): Heleidomermis cataloniensis n. sp. from Culicoides circumscriptus Kieffer in Spain and a species of Cretacimermis Poinar, 2001 from a ceratopogonid in Burmese amber.

Heleidomermis cataloniensis n. sp. (Nematoda: Mermithidae) is described from Culicoides circumscriptus Kieffer (Diptera: Ceratopogonidae) in Spain. Diagnostic characters include prominant elevations with multiple genital papillae on either side of the cloacal opening, only one row of genital papillae on the lateral surface of the tail, the tapering tip of the spicule and a reduced vagina. A male intersex of C. circumscriptus parasitised by H. cataloniensis n. sp. has mouthparts resembling those of the female. Two 100 million year-old fossil specimens of an un-named species of Cretacimermis Poinar, 2001, from an Early Cretaceous Burmese amber biting midge of the genus Leptoconops Skuse, show the antiquity of ceratopogonid-mermithid associations.