A reevaluation of specimens of Mesocoelium monas (Platyhelminthes: Digenea: Mesocoeliidae) from the Natural History Museum, UK and the United States National Parasite Collection, USA Author Calhoun, Dana M. Author Dronen, Norman O. text Zootaxa 2012 3589 1 29 journal article 10.5281/zenodo.209761 2b78cedc-fd40-4bff-98c5-12aacd319fc4 1175-5326 209761 Mesocoelium crossophorum— USNPC 0 72881.00 (Figure 10; Table 2) Host: Lutjanus cyanopterus (Cuvier) , Cubera snapper ( Perciformes : Lutjanidae ). Locality: Nueva Esparta State, Venezuela . (Native) Description: Based on one specimen: Body 1,175 by 480; forebody 520 long, representing 42% of body length. Mouth subterminal; oral sucker spherical, 175 by 160; prepharynx absent; pharynx spherical, 78 by 78; ratio of width of pharynx to oral sucker width, 1:2.1; esophagus 39 long; ceca surpassing ovary posteriorly, occupying 20% of postovarian space. Ventral sucker subspherical, situated posterior portion of anterior 1/3 of body, 149 by 140; ratio of ventral sucker width to oral sucker width 1:1.1. Testes oval to subspherical, opposite; right testis 80 by 80; left testis 76 by 60. Genital pore submedian, located immediately anterior to cecal bifurcation. Cirrus sac clavate, 108 long, representing 9% of body length. Ovary spherical, 100 by 96; postovarian space 605 long, representing 51% of body length. Uterus extensive, filling hindbody. Vitelline follicles distributed in lateral fields from level of posterior of oral sucker to level of cecal ends posteriorly. Eggs 36 (33–38) by 22 (20–24). Excretory system I-shaped shaped. FIGURE 9. Mesocoelium cf americanum— NHMUK 1979.9.12 17-19 from Duttaphrynus melanostictus , ventral view of adult. FIGURE 10. Mesocoelium crossophorum— USNPC 0 72881.00 from Cutjanus cyanopterus , ventral view of adult. Remarks: This specimen has the forebody contracted where the pharynx is pulled anteriorly into the oral sucker. Additionally, this specimen has a shorter postovarian space and the uterus contains relatively few eggs, suggesting that it is a young adult. Although this specimen has ceca surpassing the ovary posteriorly and a prebifurcal genital pore, and is assigned to the monas body type , it cannot be assigned specifically to M . monas . This specimen differs from M . monas by having vitelline fields that terminate near the cecal ends posteriorly compared with terminating well short of the cecal ends; a narrower oral sucker (175 compared with 382); a narrower pharynx (78 compared with 138); and a narrower ventral sucker (140 compared with 344). Mesocoelium danforthi and M . crossophorum are similar to this specimen by having a prebifurcal and submedian genital pore; an oval body that is widest from level of ventral sucker to midlevel of body or more posteriorly; gonads that overlap the area of the ventral sucker; the posterior extent of the vitelline fields terminating near to the cecal ends posteriorly and the specimen was collected from the New World. Mesocoelium danforthi can be distinguished from this specimen by having a larger ratio of the ventral sucker width to the oral sucker width (1:1.7–1:1.9 compared with 1:1.3), a larger percentage that the ceca surpass the ovary into the postovarian space (24–32% compared with 20%), a larger ratio of the pharynx width to the oral sucker width (1:2.8–1:3.2 compared with 1:2.2). This specimen is consistent with M . crossophorum by having a similar body length (1,175 compared with (1,000–1,100), a similar oral sucker width (160 compared with 160–175), a similar pharynx width (78 compared with 64), a similar ventral sucker width (140 compared with 130), a similar length of the postovarian space (605; 51% of the body length compared with 468; 44%), and a similar cirrus sac length (108; 9% of the body length compared with 114; 10%).