Mesocoelium leiperi

López-García, Ashley Samara & García-Prieto, Luis, 2017, A reevaluation of the specimens of Mesocoelium (Trematoda: Mesocoeliidae) in the Colección Nacional de Helmintos, Mexico, Zootaxa 4273 (2), pp. 151-176 : 164-168

Leiperi body type

Mesocoelium cf. gonocephali CNHE-1067b (1 slide: one specimen) ( Figure 11 ), Plestiodon sp. (= Eumeces sp.) ( Squamata : Scincidae ) from Cuicatlán, Oaxaca, Mexico.

Characterization. Based on 1 specimen. Body oval, covered with numerous spines that gradually diminish to posterior end, disappearing at posterior end of intestinal ceca; oral sucker subspherical, wider than long; prepharynx very short, almost absent; pharynx wider than long; cecal bifurcation slightly posterior to midforebody; intestinal ceca surpass ovary posteriorly and end slightly posterior to mid-body. Testes slightly diagonal at level of ventral sucker; cirrus sac between pharynx and ventral sucker; vitelline fields extend from the mid-level of oral sucker, slightly surpass cecal ends and enter into the postovarian space; seminal vesicle bipartite; genital pore postbifurcal, median; ovary sinistral. Uterus widely distributed but located mostly under ventral sucker. Excretory system not visible ( Table 7).

Remarks. Zerecero (1951) identified the specimen CNHE-1067b as M. meggitti (= M. travassosi ), but this material differs from M. meggitti by some diagnostic characteristics: 1) the position of the genital pore (prebifurcal and medial in M. meggitti and postbifurcal and medial in the CNHE specimen); 2) body shape (attenuated, typically clavate and relatively large in M. meggitti and oval in the specimen studied by Zerecero); and 3) seminal vesicle shape (tripartite in M. meggitti in contrast with bipartite in the CNHE specimen). Among the species of the leiperi body type group to which our specimen belongs, it is similar to M. gonocephali in traits such as the position of the genital pore, the anterior and posterior extent of the vitelline fields, the ratio of the ventral sucker width to oral sucker width (1: 1.2 in CNHE vs. 1: 1.2 in the original description), the percentage of postovarian space occupied by ceca (20.48 in CNHE specimen vs. less than 26 in the key [not mentioned in original description]), the ratio of pharynx width to oral sucker width (1: 2.1 in CNHE vs. 1:2.7 or less in the key [not mentioned in original description]), egg size (0.032 x 0.021 in CNHE vs. 0.029–0.038 x 0.022–0.024 in the original description), and the percentage of total body length occupied by the cirrus sac length (7.31 in CNHE vs. 4–7 in the original description) (Dronen et al. 2012). However, the specimen cannot be assigned to M. gonocephali because it is distinct from this species in the dimension of the forebody, cirrus sac and postovarian space, as well as by the percentage occupied by the forebody with respect to the total body length and the postovarian space related to the total body length. Another important difference lies in the host species and the geographical distribution of our specimen and M. gonocephali ; this species has been reported as a parasite of Gonocephalus grandis ( Squamata : Agamidae ) in Malaysia ( Singh 1967), and the CNHE specimen was collected in Plestiodon spp. (= Eumeces sp.) ( Squamata : Scincidae ) from Mexico. On the basis of the differences referenced above, we decided to identify the CNHE-1067b specimen as M. cf. gonocephali .

Mesocoelium sp. leiperi body type CNHE-876b (1 slide: one specimen) ( Figure 12 ), R. marina ( Anura : Bufonidae ) from Tilarán , Guanacaste, Costa Rica.

Mesocoelium sp. leiperi body type CNHE-1067d (2 slides: two specimens) ( Figure 13 ), Plestiodon spp. (= Eumeces sp.) ( Squamata : Scincidae ) from Cuicatlán , Oaxaca, Mexico.

Characterization. Based on 3 specimens. Body oval (CNHE-876b) or slightly wider at level of hindbody and relatively large (CNHE-1067d), covered with numerous spines that gradually diminish and disappear at posterior end of intestinal ceca (CNHE-1067d) or almost reaching posterior end of uterus (CNHE-876b); oral sucker spherical (CNHE 876b) or subspherical, longer than wide (CNHE1067d); prepharynx very short, almost absent; pharynx spherical (CNHE-876b) or subspherical, wider than long (CNHE-1067d); cecal bifurcation slightly posterior to mid-forebody; intestinal ceca surpass ovary posteriorly and end slightly posterior to mid-body. Testes lateral or slightly diagonal at level of ventral sucker; cirrus sac between cecal bifurcation and ventral sucker; vitelline fields extend from the mid-level of oral sucker or slightly posterior, surpass cecal ends in at least one side and enter into the postovarian space. Seminal vesicle bipartite (CNHE-1067d) or tripartite (CNHE-876b); genital pore postbifurcal, median; ovary dextral (CNHE-1067d) or sinistral (CNHE-876). Uterus widely distributed but located mostly under ventral sucker. Excretory vesicle visible partially at posterior end ( Table 8).

Remarks. Caballero & Brenes (1958) and Zerecero (1951) identified the specimens CNHE-876b and CNHE- 1067d, respectively, as M. meggitti (= M. travassosi ), but several characteristics of this material are inconsistent with those of M. meggitti : 1) the position of the genital pore (prebifurcal and medial in M. meggitti [mesembrinum body type] and markedly postbifurcal and medial [ leiperi body type] in the specimens held at CNHE) and 2) body shape (attenuated, typically clavate and relatively large in M. meggitti and oval in our material). The remaining difference lies in the seminal vesicle shape because M. meggitti has a tripartite seminal vesicle, and in two of the studied specimens (CNHE-1067d), we observed a bipartite seminal vesicle. Although the specimen CNHE-876b has a tripartite seminal vesicle, the differences mentioned above prevent its assignment to M. meggitti .

Characteristics Mesocoelium sp. body type leiperi

CNHE-876b CNHE-1067d

n=1 n=2

The morphometry of the CNHE-876b and CNHE-1067d specimens do not agree with any of the 11 species within the leiperi body type since they have a combination of characteristics from several of these species and/or the absence of diagnostic characteristics, precluding its identification. Some examples of this problem are as follows: the presence of a tripartite vesicle in the CNHE-876b specimen (which is bipartite in all the species included in this group); the ratio of oral sucker width to ventral sucker width of one of the CNHE-1067d specimens was higher than 1:1.6; the percentage of the intestinal ceca that surpasses the ovary in one of CNHE-1067d specimens was 37%, while this percentage was smaller than 26% or greater than 37% in the species with leiperi body type; and finally, the percentage that represents the length of the cirrus sac in relation with the total body length of the specimens. In addition, our specimens share some traits such as the position of the genital pore, the percentage occupied by the cirrus sac of the total body length, the position of the gonads in relation to the ventral sucker, the egg width and the presence of body spines. However, these features are insufficient to determine them to a specific level, so they were designated Mesocoelium sp. leiperi body type.

Figures

FIGURE 11. Mesocoelium cf. gonocephali (CNHE- 1067 b) parasite of Plestiodon spp. (= Eumeces sp.) from Cuicatlán, Oaxaca, Mexico. Ventral view of the specimen (A) and detail of the cirrus sac (B).

FIGURES 12 – 13. 12. Mesocoelium sp. leiperi body type (CNHE- 876 b) parasite of Rhinella marina from Tilarán, Guanacaste, Costa Rica. Ventral view of the specimen (A) and detail of the cirrus sac (B). 13. Mesocoelium sp. leiperi body type (CNHE- 1067 d) parasite of Plestiodon spp. (= Eumeces sp.) from Cuicatlán, Oaxaca, Mexico. Ventral view of the specimen (A) and detail of the cirrus sac (B).