Bess beetles (Passalidae) display important roles in forestall ecosystems, particularly in energy extraction from dead wood. These organisms maintain complex biological interactions with their gut symbiotic communities, including bacteria, protists, and metazoans. Very little is known about symbionts since most of the species of Passalidae haven't been studied from a parasitological point of view. Here we describe a new genus and 2 new species of nematodes of the family Hystrignathidae associated with 2 beetle species of the tribe Proculini collected in the State of Oaxaca, Mexico. Tuhmai garciaprietoi n. gen., n. sp., found in Vindex agnoscendus is characterized by the presence of an unarmed cervical cuticle, a subcylindrical procorpus and a conspicuous isthmus, a monodelphic-prodelphic reproductive system, and a short subulate tail. Urbanonema osorioi n. sp., found in Verres hageni mainly differs from other species of Urbanonema by the number and disposition of cervical spines, as well as by a subulate tail. For each new taxon, we describe the external and internal morphology, and we generated molecular data (nuclear ribosomal DNA) to place the new taxa in a phylogenetic context.

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