Raillietina sp. (1)

Site of infection: Small intestine

Host species: Heteromys gaumeri, Ototylomys phyllotis, Peromyscys yucatanicus, and Sigmodon toltecus

Localities: Hobonil ranch, Santa Cruz cattle ranch, Aak ecological park, Kuncheil cattle ranch (Yucatan), Ich ha lol xaan ecological park, Zoh Laguna community (Campeche), Jolie Jungle eco-hotel, and Balam Nah eco-hotel (Quintana Roo)

Specimens deposited: CNHE 10968, 10969, 10972, 11959, 11960‒11971

GenBank accession numbers: OR271637‒OR271648

Comments: The morphological characteristics observed in our specimens agreed with those established for the genus Raillietina, i.e., rostellum with double crowns of alternating hooks; armed suckers; craspedote proglottids; single reproductive organs; unilateral genital pores; small cirrus-sac, not reaching or just crossing the osmoregulatory canals; numerous testes; ovary median; and several eggs per capsule (Khalil et al. 1994). Our specimens had 72–80 rostellar hooks; suckers 65–135 long by 74–137 wide (Figure 3A); anterior hooks 16–20 long, posterior hooks 19-22.5 long; 14–17 testes; 34– 105 egg capsules; and 1– 4 eggs per capsule. In North America, two species of Raillietina have been described in rodents, Raillietina bakeri Chandler from Sciurus niger rufiventer Geoffroy and Raillietina sigmodontis Smith from Sigmodon hispidus texianus (Audubon & Bockman). Raillietina bakeri and Ra. sigmodontis were described with the same number (66) and length (20–22) of rostellar hooks but differences in the number of testes (30–40 vs 15–19) and egg capsules (80–90 vs 30–35) and eggs per capsule (6–10 vs 15–25) were observed (Chandler 1942; Smith 1954). In the original descriptions of Ra. sigmodontis, Smith (1954) mentioned that no morphological variations had been reported for Ra. bakeri and concluded that Ra. sigmodontis represented a new species. However, Baylis (1945) reported variations in the number (88–97) and length (25–30) of rostellar hooks for Ra. bakeri collected from Sigmodon hispidus Say & Ord, differences that could be related to its occurrence in a different host species. In Ra. sigmodontis collected from S. toltecus (originally reported as S. hispidus), H. gaumeri and O. phyllotis in Belize, Bersot (2001) also reported variations in the number (84) and length (25.6) of rostellar hooks and number (21–26) of testes, compared with the original description of this species. Considering these wide variations in the reported morphology of both Raillietina species and that our specimens shared traits with them, we cannot assign Raillietina to the species level. Indeed, Cameron & Reesal (1951) mentioned that substantial variation in dimensions and numbers of the characters used for the parasite diagnosis such as hooks, testes and egg capsules even within the cestodes from the same host can be observed in Raillietina.

In Mexico, Raillietina baeri Meggitt & Subramanian was recorded from Heteromys irroratus (Gray) in Hidalgo (Carmona-Huerta 1994), and Raillietina celebensis (Janicki) from Oryzomys sp. in Oaxaca (Flores-Barroeta & Hidalgo-Escalante 1960). In addition, unidentified species of Raillietina have been reported from Heteromys pictus Thomas in Durango (García-Prieto et al. 2012), Dipodomys phillipsi Gray in Puebla and Veracruz (García-Prieto et al. 2012), Oryzomys couesi (Alston) and Oryzomys melanotis Thomas in San Luis Potosí (Underwood et al. 1986), H. irroratus in Tlaxcala (García-Prieto et al. 2012), Chaetodipus sp. in Zacatecas (Martínez-Salazar et al. 2016), and S. toltecus in Yucatan (Panti-May et al. 2018). Our finding extends the geographical distribution of the genus Raillietina including the states of Campeche and Quintana Roo in Mexico. In addition, this cestode genus is reported for the first time in P. yucatanicus. Further morphological and molecular studies on Raillietina species infecting small rodents in North America are needed to clarify their identity.