Scaphiostomum sp.

Panti-May, Jesús Alonso, Moguel-Chin, Wilson Isaias, Hernández-Mena, David Iván, Cárdenas-Vargas, Miguel Humberto, Torres-Castro, Marco, García-Prieto, Luis, Digiani, Maria Celina, Hernández-Betancourt, Silvia F. & Vidal-Martínez, Víctor Manuel, 2023, Helminths of small rodents (Heteromyidae and Cricetidae) in the Yucatan Peninsula, Mexico: an integrative taxonomic approach to their inventory, Zootaxa 5357 (2), pp. 205-240 : 209-210

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 ). 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 .

Figures

FIGURE 2. A.Adult specimen of Scaphiostomum sp. from Heteromys gaumeri, ventral view. B. Adult specimen of Skrjabinus sp. from Heteromys gaumeri, ventral view. C. SEM micrograph of Skrjabinus sp. from Heteromys gaumeri showing the ventral surface and the acetabulum, ventral view. D. Adult specimen of Microphallidae gen. sp. from Peromyscus yucatanicus, ventral view.