Calhoun, Dana M. & Dronen, Norman O., 2012, A reevaluation of specimens of Mesocoelium monas (Platyhelminthes: Digenea: Mesocoeliidae) from the Natural History Museum, UK and the United States National Parasite Collection, USA, Zootaxa 3589, pp. 1-29 : 21

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Mesocoelium cf monodi— NHMUK 1980.7. 14 50-54

( Figure 13, Table 3 View TABLE 3 )

Host: Bufo marinus (Linnaeus) , cane toad ( Anura ; Bufonidae ).

Locality: Papua New Guinea. (Introduced)

Description: Based on two specimens: Body elliptical, tapered posteriorly, 2,094 (1,404–2,784) by 511 (620–962); forebody 832 long, representing 40 % of body length (n= 1). Mouth nearly terminal; oral sucker subspherical, 223 (190–255) by 220 (210–231); prepharynx absent; pharynx spherical to broadly subspherical, 66 (50–81) by 91 (78–104); ratio of width of pharynx to width of oral sucker 1: 2.5 (1: 2.2 – 1: 2.7); esophagus 105 (90–121) long; ceca surpassing ovary posteriorly, occupying 42 % (37–47 %) of postovarian space. Ventral sucker spherical to subspherical, situated in anterior 1 / 3 of body, 146 (110–182) by 154 (125–182); ratio of width of ventral sucker to width of oral sucker 1: 1.5 (1: 1.3 – 1: 1.7). Testes subspherical, opposite; right testis 91–104 wide; left testis 169–205. Genital pore submedian, located at level of posterior 1 / 3 of pharynx. Cirrus sac 191 long, representing 9 % of body length (n= 1). Ovary subspherical to laterally elongate, 148 (114–182) by 143 (91–195); postovarian space 1,047 (1,061–1,846) long, representing 50 % (47–66 %) of body length. Uterus extensive, filling hindbody. Vitelline follicles distributed in lateral fields from level of posterior margin of oral sucker to level of cecal ends or more posterior. Eggs 33 (29–36) by 21 (18–23). Excretory system not visible.

Remarks: Both specimens were in poor condition and appear to be contracted, displacing the genital pore anteriorly where it appears to be nearly at the level of the pharynx in one specimen. Specimens are rolled to one side and have an irregular body shape. Additionally, the ceca have been twisted at, or just below the cecal bifurcation.

Although these specimens have ceca that surpass the ovary posteriorly and a prebifurcal genital pore, and are assigned to the monas body type, they cannot be assigned specifically to M. monas . These specimens differ from M. monas by having vitelline follicles that terminate near to, or surpass the cecal ends posteriorly compared with terminating well short of the cecal ends, a narrower oral sucker (210–231 compared with 382), a narrower pharynx (78–104 compared with 138), a narrower ventral sucker (125–182 compared with 344), and a slightly larger percentage of the ceca that surpass the ovary into the postovarian space (37–47 % compared with 31 %).

Both specimens are consistent with M. monodi by having a submedian genital pore, a similar ratio of the ventral sucker width to the oral sucker width (1: 1.3 – 1: 1.7 compared with 1: 1.3), a similar ratio of the oral sucker width to the pharynx width (1: 2.2 – 1: 2.7 compared with 1: 2.8), and a similar length of the postovarian space (1,061–1,846; 47–66 % of body length compared with 1,680; 56 %). Mesocoelium monodi was originally described from Chamaeleon gracilis Hallowell (syn. Chamaeleon gracilis Gray ) from Central Arica rather than B. marinus from Papua New Guinea). Additionally, these specimens have a longer forebody (832; 40 % of body length compared with M. monodi (778; 26 %)

Given the similarities between these specimens ( NHMUK 1980.7. 14 50-54) and those in USNPC 0 97835.00 (both sets are from Papua New Guinea), it is possible that together they may represent an undescribed species; however, the variation in egg size and poor condition of the USNPC specimens make description impractical. The specimens from USNPC have a similar ratio of the pharynx width to the oral sucker width (1: 2.7 compared with 1: 2.5 [1.2.0– 1: 2.7]), a similar egg size (36 [29–42] by 20 [18–21] compared with 33 [29–36] by 21 [18–23]), and both sets of specimens have the vitelline fields distributed in lateral fields from the level of the posterior margin of the oral sucker to the level of the cecal ends posteriorly.


Natural History Museum, London


United States National Parasite Collection