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Ascaridoids are among the commonest groups of zooparasitic nematodes (roundworms) and occur in the alimentary canal of all major vertebrate groups, including humans. They have an extremely high diversity and are of major socio-economic importance. However, their evolutionary history remains poorly known. Herein, we performed a comprehensive phylogenetic analysis of the Ascaridoidea. Our results divided the Ascaridoidea into six monophyletic major clades, i.e., the Heterocheilidae, Acanthocheilidae, Anisakidae, Ascarididae, Toxocaridae, and Raphidascarididae, among which the Heterocheilidae, rather than the Acanthocheilidae, represents the sister clade to the remaining ascaridoids. The phylogeny was calibrated using an approach that involves time priors from fossils of the co-evolving hosts, and dates the common ancestor of the Ascaridoidea back to the Early Carboniferous (approximately 360.47–325.27 Ma). The divergence dates and ancestral host types indicated by our study suggest that members of the Ascaridoidea first parasitized terrestrial tetrapods, and subsequently, extended their host range to elasmobranchs and teleosts. We also propose that the fundamental terrestrial-aquatic switches of these nematodes were affected by changes in sea-level during the Triassic to the Early Cretaceous.

Morphological data are used to describe a new nematode species, Heterocheilus floridensis sp. n. (Heterocheilidae) from the digestive tract of the Florida manatee Trichechus manatus latirostris (Harlan) (Trichechidae, Sirenia) from Florida, USA. Examination by light and scanning electron microscopy revealed that the new species differs from the related Heterocheilus tunicatus Diesing, 1839 mainly by having dentigerous ridges on the inner surface of the lips, a median unpaired papilla located anterior to the cloaca, and a considerably larger body size. Sequence data for subunits I and II of mitochondrial cytochrome oxidase gene, 18S small subunit and 28S ribosomal RNA genes were provided for molecular characterisation of the new species. However, the current unavailability of homologous sequence data for congeneric specimens precluded a molecular assessment of the morphological species hypothesis, and ascaridoid phylogenetic hypotheses could not be advanced. Specimens of Heterocheilus sp. collected from the Antillean manatee Trichechus manatus manatus Linnaeus in Puerto Rico, on loan from the US National Museum of Natural History, were morphologically consistent with the new species, so apparently all congeneric nematodes reported from both subspecies of the West Indian manatee Trichechus manatus Linnaeus and previously identified as H. tunicatus belong rather to H. floridensis sp. n. Heterocheilus hagenbecki (Khalil et Vogelsang, 1932) Sprent 1980 is here considered to be a species inquirenda. A key to valid species of Heterocheilus Diesing, 1839 is provided.

Based on light and scanning electron microscopical observations, Typhlophoros kwenae n. sp. (Heterocheilidae), a new nematode parasite, is described from the stomach of the Nile crocodile Crocodylus niloticus Laurenti in South Africa. In having three lips with well-developed posterior prolongations and prominent interlabial longitudinal cuticular ridges, four pairs of precloacal papillae and complex spicules divided into handle and broad alate blade in males, as well as the position of the vulva near mid-body in females, the specimens conform to the generic diagnosis of Typhlophoros von Linstow, 1906. They can, however, be distinguished from the two previously described congeners, T. lamellaris von Linstow, 1906 and T. spratti Sprent, 1999, by the number of complete interlabial ridges, the length of spicules in males and the position of the vulva as well as the length of the tail in females. This is the first record of the genus Typhlophoros from the Afrotropical Realm.

Brevimulticaecum Mozgovoy, in Skrjabin, Shikhobalova, and Mozgovoy, 1951 was redefined and presented as a valid genus by Sprent. The new denomination proposed by Sprent is based on the following morphological characteristics: flat lips with a late margins and notches, without dentigerous ridges. The excretory pore in Brevimulticaecum is located in front of or at the nerve ring, and the ventriculus presents short appendices. One Lepidobatrachus laevis Budgett, 1899 was collected in Ingeniero Juarez, Formosa, Argentina and 34 Physalaemus albonotatus and 19 Pseudis paradoxa were collected near the city of Corrientes, Corrientes, Argentina between March 2010 and February 2011. At necropsy, all the organs were examined for parasites by dissection. Capsules were counted and isolated from host tissues. Larvae were removed from capsules using preparation needles and studied first in vivo, enumerated, and then killed in hot distilled water, preserved in 70% ethyl alcohol and examined as temporary mounts.

Sciaenid fishes (croakers), Argyrosomus regius, Pseudotolithus (Fonticulus) elongatus and Pseudotolithus (Pseudotolithus) senegalensis were isolated from fish samples collected monthly from November 2004 to June 2006 at flood tide in Buguma creek, Niger Delta, Nigeria. The fish samples were caught by the use of hooks and lines and cast nets. A total of seven hundred and eighty nine specimens comprising A. regius (12), P. (Fonticulus) elongatus (753) and P. (Pseudotolithus) senegalensis (24) were examined for gastrointestinal helminth parasites. All helminth parasites observed were nematodes. No infection was recorded in A. regius. P. (Pseudotolithus) senegalensis had the highest prevalence (41.7%), followed by P. (Fonticulus) elongatus (23.4%). A total of 57 helminth parasites were recorded, of which 54 were found in P. (Fonticulus) elongtus, and 20 in P. (Pseudololithus) senegalensis. Goezia sigalasi (Ascarididae) and Pseudanisakis sp. (Heterocheilidae) had the highest prevalence in both species of sciaenid fishes infected.