Scaphiostomum sp.

Scaphiostomum sp.

Site of infection: Small intestine

Host species: Heteromys gaumeri and Sigmodon toltecus

Localities: Hobonil ranch, Santa Cruz cattle ranch ( Yucatan) and Zoh Laguna community ( Campeche)

Specimens deposited: CNHE 10973, 11954‒6

GenBank accession number: OR271636

Comments: The collected specimens have morphological features that allowed us to identify them as a species of the genus Scaphiostomum ( Mas-Coma et al. 1986) , i.e., body filiform with tegument unspined; suckers slightly spaced; pharynx small; testes and ovary in tandem (ovary inter-testicular), close to each other, inter-caecal; cirrus-sac small; genital pore anterior to anterior testis; vitellarium not reaching at the level of ventral sucker and terminating posteriorly at level of anterior testis; uterus very long, forming numerous loosely arranged coils, anteriorly very close to ventral sucker. Our specimens had suckers nearly equal in size; prepharynx absent; esophagus absent; anterior testis bilobed; and vitellarium slightly separated from the posterior region of the ventral sucker ( Figure 2A View FIGURE 2 ). The main measurements of our specimens were: body length 5250‒9625, maximum width 912.5‒1225; oral sucker 262.5‒375 long by 250‒375 wide; ventral sucker 250‒312.5 long by 237.5‒325 wide; eggs 29.5‒31.5 long by 19.5‒20 wide. Two species of Scaphiostomum have been reported in American rodents ( Mas-Coma et al. 1986), Scaphiostomum microti (Kruidenier & Gallicchio) and Scaphiostomum pancreaticum Mclntosh. However , these species can be differentiated from our specimens by having a longer body ( 9710‒12750 in Sc. pancreaticum ), smaller oral sucker ( 128‒220 in Sc. microti and 235 in Sc. pancreaticum ), ventral sucker ( 150‒220 in Sc. microti and 240 Sc. pancreaticum ), and larger eggs ( 32‒38 in Sc. microti and 35 in Sc. pancreaticum ). In Belize, Bersot (2001) reported Sc. pancreaticum in H. gaumeri and O. phyllotis , however, he also stated that the identity of this trematode should be confirmed. Considering that the brief morphological description of Bersot´ (2001) specimens is closer to our specimens than that of Sc. pancreaticum , it is likely that the trematode from the Yucatan Peninsula represent a new, undescribed Scaphiostomum species.

This is the first record of the genus Scaphiostomum in Mexico and for S. toltecus .