Heligmonellidae gen. sp.

Site of infection: Mesentery

Host species: Sigmodon toltecus

Localities: Vallazoo (Yucatan)

Specimens deposited: CNHE 12023

GenBank accession numbers: OR271670

Comments: Only two female specimens were collected from the mesentery of S. toltecus . They exhibited characteristics of the family Heligmonellidae, such as presence of cephalic vesicle; monodelphy, and absence of caudal spine. However, the synlophe was absent (Figure 4L). Among heligmonellid nematodes of rodents, a strong reduction or even absence of synlophe is observed in species of the genus Hypocristata Durette-Desset. Three species of this genus have been described from sigmodontine rodents in Northern South America, including Sigmodon hirsutus (Burmeister) (originally described as S. hispidus) in Venezuela (Durette-Desset 1971; Durette-Desset & Guerrero 2006). The present specimens are very probably related to Hypocristata but the scarcity and condition of specimens and especially the lack of males prevent a more accurate identification.