Ascaridoid nematodes parasitize the gastrointestinal tract of vertebrate definitive hosts and are represented by more than 50 described genera. We used 582 nucleotides (83% of the coding sequence) of the mitochondrial gene cytochrome oxidase subunit 2, in combination with published small- and large-subunit nuclear rDNA sequences (2,557 characters) and morphological data (20 characters), to produce a phylogenetic hypothesis for representatives of this superfamily. This combined evidence phylogeny strongly supported clades that, with 1 exception, were consistent with Fagerholm's 1991 classification. Parsimony mapping of character states on the combined evidence tree was used to develop hypotheses for the evolution of morphological, life history, and amino acid characters. This analysis of character evolution revealed that certain key features that have been used by previous workers for developing taxonomic and evolutionary hypotheses represent plesiomorphic states. Cytochrome oxidase subunit 2 nucleotides show a strong compositional bias to A+T and a substitution bias to thymine. These biases are most apparent at third positions of codons and 4-fold degenerate sites, which is consistent with the nonrandom substitution pattern of A+T pressure. Despite nucleotide bias, cytochrome oxidase amino acid sequences show conservation and retention of critical functional residues, as inferred from comparisons to other organisms.

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Phylogeny of the Ascaridoidea (Nematoda: Ascaridida) based on three genes and morphology: hypotheses of structural and sequence evolution.

Ribosomal DNA and Phylogeny of the Ascaridoidea (Nemata: Secernentea): Implications for Morphological Evolution and Classification☆

4 – Metazoan Symbionts of Crustaceans

Taking into account the difficulties of taxonomic identification of larval anisakid nematodes based on morphological characters, genetic analyses were performed, together with those usually applied, in order to identify anisakid larvae found in the flounder Paralichthys isosceles from the littoral of the state of Rio de Janeiro, Brazil. The analysis of 1,820 larvae revealed a new species, similar to Hysterothylacium MD, Hysterothylacium 2, Hysterothylacium KB and Hysterothylacium sp regarding the absence of the larval tooth, an excretory pore situated below the nerve ring level, and slender lateral alae. Moreover, the new species differs from Hysterothylacium fortalezae and Hysterothylacium reliquens with regard to the number and size of spines present on the tail end and from Hysterothylacium patagonicus by the absence of interlabia. The maximum parsimony and neighbour joining tree topologies based on the 18S ribosomal DNA gene, complete internal transcribed spacer region and cytochrome oxidase 2 (COII) gene demonstrated that the Brazilian larvae belong to Raphidascarididae and represent a unique genetic entity, confirmed as a new Hysterothylacium species. Furthermore, the new species presents COII genetic signatures and shares polymorphisms with Raphidascarididae members. This is the first description of a new anisakid species from Brazil through the integration of morphological and molecular taxonomy data.

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Genetic and morphological characterisation of a new species of the genus Hysterothylacium (Nematoda) from Paralichthys isosceles Jordan, 1890 (Pisces: Teleostei) of the Neotropical Region, state of Rio de Janeiro, Brazil

Numerous fishes and invertebrates in the northern Gulf of Mexico contain larvae of four forms of Hysterothylacium: ?//. reliquens (=type MA, Mississippi A), type MB, H.fortalezae (=type MC), and type MD. The third-stage larvae (possible second-stage larva of type MB) of all are described and illustrated; furthermore, corresponding fourth-stage larvae of all but type MB are described. A key to all these inshore and nearshore larvae is included. Biological differences among related species are exemplified using H. reliquens and Iheringascaris inclines. The second-stage larva of /. inclines survives much longer in cold water than that of H. reliquens, and the fourth-stage larva of /. inclines is unique because it invades alimentary tissue of the final host. Adult nematodes of the genus Hysterothylacium Ward and Magath, 1917 are restricted to the digestive tract, with one exception (Machida et al., 1978), of fishes, whereas their larvae parasitize various tissues of numerous fishes and invertebrates (e.g., Norris and Overstreet, 1976). Deardorff and Overstreet (1981) reviewed the genus, previously known as Thynnascaris Dollfus, 1933 or Contra- caecum sensu lato, and examined adults of six species from the Gulf of Mexico. In this paper, we describe the larvae of four forms of Hysterothylacium fol- lowing the nomenclature initiated by Norris and Overstreet (1976) and provide a listing of hosts. The number of species in the inshore northern Gulf of Mexico may be greater because more than one species could have morphologically similar larvae. However, some known adults from the Gulf of Mexico are rare and not found in inshore northern regions where most larval specimens were collected. On the other hand, two forms may be different phases of the same species, and we may have included larvae of the related Iheringascaris inquies (Linton, 1901) Deardorff and Overstreet, 1981 which is not Hysterothylacium sensu stricto, even though placed in the genus Thynnascaris by most recent workers (see Deardorff and Overstreet, 1981). Our studies of the ascaridoid fauna in the Gulf of Mexico have differentiated at least one species that is a potential public health hazard. Norris and Overstreet (1976) established that Hysterothylacium type MB rapidly penetrated the alimen- tary tract of white mice. That study has been expanded (Ebert and Norris, per- sonal communication), and the worm also causes lesions and diffuse mucosal hemorrhaging in the rhesus monkey (Overstreet and Meyer, 1981). Fetter (1969a, b) hypothesized that H. aduncum (Rudolphi, 1802) Deardorff and Overstreet, 1981 (as Thynnascaris adunca) from Sardina pilchardus (Walbaum) was the caus- ative agent for several cases of anisakiasis in man; however, Vermeil et al. (1975) determined that the suspected nematode did not penetrate the rabbit stomach and questioned the hypothesis. Under stated experimental conditions, Hysterothy- lacium type MA did not penetrate tissues in mice (Norris and Overstreet, 1976).

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Larval Hysterothylacium (=Thynnascaris) (Nematoda: Anisakidae) from Fishes and Invertebrates in the Gulf of Mexico

Within a few hours after being administered to the rhesus monkey (Macaca mulatta), Hysterothylacium type MB larvae penetrated the stomach wall, causing hemorrhage and attracting eosinophils Inocula up to 300 larvae, however, did not cause peripheral hypereosinophilia This species is the first ascaridoid which normally matures in fish that has been shown to penetrate the alimentary tract of a primate Consequently, human consumption of raw seafood from at least the northern Gulf of Mexico free from infections, with Anisakis spp, Phocanema decipiens, or other species that mature in mammals or birds does not necessarily assure freedom from anisakiasis as previously assumed

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George W. Meyer

Papers

Hemorrhagic lesions in stomach of rhesus monkey caused by a piscine ascaridoid nematode.