Mesocoelium Odhner, 1910

Dronen, Norman O., Calhoun, Dana M. & Simcik, Steven R., 2012, Mesocoelium Odhner, 1901 (Digenea: Mesocoelidae) revisited; a revision of the family and re-evaluation of species composition in the genus 3387, Zootaxa 3387 (1), pp. 1-96 : 7

Genus Mesocoelium Odhner, 1910

Diagnosis. With characteristics of family. Body elongate to oval or elliptical, often rounded at both ends, may be somewhat tapered posteriorly, (typically widest from level of ventral sucker to near midlevel of body), some species with body attenuated posteriorly, typically clavate (widest at level of forebody). Preoral lobe sometimes evident; oral sucker subterminal; mouth opening ventrally, centrally located in oral sucker in some species, opening more anteriorly in others (sometimes approaching being terminal); prepharynx short, nearly absent; pharynx smaller than oral sucker, muscular, usually wider than long; esophagus present, much longer than prepharynx; ceca short (not surpassing ovary posteriorly) to moderately long (surpassing ovary, extending some distance into postovarian space, rarely extending beyond midlevel of postovarian space). Ventral sucker well above midlevel of body, usually in anterior ⅓ of body, smaller than oral sucker. Testes spherical to subspherical, sometimes laterally elongate, generally smooth, oblique to nearly side by side, at level of ventral sucker, occasionally postacetabular. Cirrus sac well developed, enclosing bipartite seminal vesicle and prostate cells, often clavate, largely between cecal bifurcation and ventral sucker, may overlap anterior margin of ventral sucker. Genital pore prebifurcal, median or submedian; bifurcal, median or submedian; or postbifurcal and median. Ovary oval to elongate, smooth, postesticular, forming triangle with testes. Seminal receptacle saccate, posteromedial to ovary. Laurer’s canal present. Uterus with highly folded ascending and descending limbs, filling most of postovarian space, ascending limb passing lateral to testes opposite of ovary; uterine loops may approach body wall; metraterm short, indistinct. Vitellaria follicular, ventral and lateral to ceca; vitelline fields may reach to midlevel of oral sucker anteriorly, posterior extent variable, terminating from some distance anterior to ventral sucker to midlevel of postovarian space, exceptionally more posterior. Excretory vesicle Y-shaped, with poorly developed arms to I-shaped; excretory pore terminal to slightly subterminal. Life cycle where known utilizes terrestrial snail first intermediate host, where cercariae may form metacercariae in first intermediate host or possibly in a second snail host; arthropods may be implicated as potential second intermediate hosts for some species. Adults in intestines of amphibians and reptiles, rarely fish; found between 49º N and 49º S latitudes.

Type species. Mesocoelium sociale ( Lühe, 1901) Odhner, 1910 .