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.

Unique two-photoreceptor scanning eye of the nematode Mermis nigrescens.

A single eye is present in females of the nematode Mermis nigrescens. A pigment cup occupies the entire cross section near the anterior tip of the worm, and the curved cuticle at the tip becomes a cornea. The shading pigment is hemoglobin instead of melanin. The eye has been shown to provide a positive phototaxis utilizing a scanning mechanism; however, the eye's structure has not been sufficiently described. Here, we provide a reconstruction of the eye on the basis of light and electron microscopy of serial sections. Hemoglobin crystals are densely packed in the cytoplasm of expanded hypodermal cells, forming the cylindrical shadowing structure. The two putative photoreceptors are found laterally within the transparent conical center of this structure where they would be exposed to light from different anterior fields of view. Each consists of a multilamellar sensory process formed by one of the dendrites in each of the two amphidial sensory nerve bundles that pass through the center. Multilamellar processes are also found in the same location in immature adult females and fourth stage juvenile females, which lack the shadowing pigment and exhibit a weak negative phototaxis. The unique structure of the pigment cup eye is discussed in terms of optical function, phototaxis mechanism, eye nomenclature, and evolution.

Recent and fossil nematode parasites (Nematoda: Mermithidae) of neotropical ants.

The following new recent species of mermithid (Nematoda) parasites of Neotropical ants are described: Meximermis ectatommi n.gen., n. sp. from workers of Ectatomma ruidum Roger in Southern Mexico, Agamomermis cephaloti n. sp. from a worker of Cephalotes minutus (Fab.) collected in Brazil, Agamomermis ecitoni n. sp. from a worker of Eciton burchellii Westwood collected in Venezuela and Agamomermis costaricensis n. sp. from a worker of Odontomachus hastatus (Fab.) collected in Costa Rica. In addition, a fossil mermithid parasite of a worker of Linepithema sp. from Dominican amber is described as Heydenius myrmecophila n. sp. These parasites represent the first descriptions of Neotropical ant mermithids and together with previous records listed here, show that ant infection by mermithids in the Neotropics is widespread and has occurred for at least 20-30 million years.

Hydromermis contorta (Kohn) and Hydromermis pseudocontorta n. sp. from chironomids of Lake Itasca and Long Lake, Minnesota.

Hydromermis contorta (Kohn) and Hydromermis pseudocontorta n. sp. are described from chironomids in Lake Itasca and Long Lake, Minnesota, respectively. The former was recovered from adult females of Glyptotendipes paripes (Edwards) and the latter from fourth-instar larvae of Chironomus sp. Hydromermis pseudocontorta n. sp. resembles H. contorta in cephalic structures, overall size, and the presence of a restricted trophosome in the female. The terminal mouth, long uterine and vulvar limbs of the vagina, and the strongly chitinized brownish spicule of H. contorta contrast with the subventral mouth, short vaginal limbs, and the light yellow spicule of H. pseudocontorta n. sp. Both nematode species emerge from the host as sexually mature adults and both species give evidence of mating while in the host. The H. contorta described by Welch is designated as a new species, Hydromermis albionis n. sp.

Strelkovimermis acuticauda n. sp. and Strelkovimermis buccalis n. sp. (Nematoda:Mermithidae) from adult chironomids (Diptera:Chironomidae) from Lake Itasca, Minnesota.

Specimens of 2 mermithid species were obtained from adults of undetermined species of chironomids emerging from Lake Itasca (Clearwater County), Minnesota. Both species have the characteristics of species in the genus Strelkovimermis. The new species are distinguishable from one another and from the 8 currently accepted species in the genus by their small size, shape of the posterior end, length of the buccal funnel, length of the cephalic papillae, location of the mouth, and morphology of the spicule region and vagina. Strelkovimrmis acuticauda n. sp. is unique in possessing an acute posterior end, an auxiliary protractor muscle, and a relatively long vagina, whereas Strelkovimermis buccalis n. sp. is distinguishable from other Strelkovimermis species by its thick cuticle and exceptionally long buccal funnel. The significance of the tail muscles is emphasized as a taxonomic feature to be used in describing future species of Strelkovimermis. A key to the 10 species of Strelkovimermis is provided.

Ultrastructure of the anterior sense organs of adult Gastromermis Boophthorae (Nematoda: Mermithidae).

The amphids of adult Gastromermis boophthorae exhibit an organization unlike any previously reported. Each amphid consists of a distal cuticular channel which opens to the exterior, and a proximal amphidial gland. The cuticular channel is double and 15-18 cilia are held in a tight bundle by the inner channel. The amphidial gland contains an extensive reticulum, and the nerve axons which give rise to the amphidial cilia are arranged around the outside of the gland; anteriorly these axons are characteristically flattened. A granular secretion is produced by the amphidial gland and passes via the reticulum to the double cuticular channel, thus bathing the ciliary bundle. The ultrastructure of the amphids is discussed in relation to functional considerations.