Mesocoelium

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 : 17

Mesocoelium crossophorum— USPNPC 0 92185.00

( Figure 11 , Table 2)

Host: Anolis biporcatus (Wiegmann) , green tree anole ( Squamata : Polychrotidae ).

Locality: Panama. (Native)

Description: Based on five specimens: Body 1,807 (1,716–1,898) by 485 (468–494); forebody 470 long (n=1), representing 26% of body length. Mouth subterminal; oral sucker spherical to subspherical, 175 (167–182) by 184 (172–195); prepharynx absent; pharynx spherical, 67 (52–81) by 79 (75–83); ratio of pharynx width to oral sucker width 1:2.2 (1:2.0–1:2.3); esophagus 130 long (n=1); ceca surpassing ovary posteriorly, occupying 20% (17–23%) of postovarian space. Ventral sucker spherical to subspherical, situated in anterior portion of middle 1/3 of body, 133 (123–143) by 131 (122–140); ratio of ventral sucker width to oral sucker width, 1:1.3 (1:1.2–1:1.4). Testes spherical, diagonal; right testis 156 by 176; left testis 155 by 176 (n=1). Genital pore submedian, located immediately posterior to posterior margin of pharynx. Cirrus sac clavate, 149 long, representing 8% (n=1) of body length. Ovary spherical to subspherical, 158 (146–169) by 127 (107–146); postovarian space 1,150 (1,020–1,280), representing 64% (56–67%) of body length. Uterus extensive, filling hindbody. Vitelline follicles distributed in lateral fields from level of anterior margin of pharynx to near level of cecal ends. Eggs 33 (29–36) by 21 (18–23). Excretory system I-shaped, excretory pore not visible.

Remarks: These specimens are contracted and the posterior end of the body is distorted, suggesting that they may have been cold fixed without coverslip pressure, precluding observations of some structures (e.g. cirrus sac, testes, excretory pore).

Although these specimens have ceca that surpass the ovary posteriorly and a prebifurcal, submedian genital pore, and are assigned to the monas body type, they cannot be assigned specifically to M. monas . These specimens can be distinguished from M. monas by having vitelline fields that terminate near to the cecal ends compared with terminating well anterior to the ceca ends, a shorter forebody (470 compared with 970), a narrower oral sucker (172–195 compared with 382), a narrower pharynx (75–83 compared with 138), a narrower ventral sucker (122–140 compared with 344), and slightly longer eggs (29–36 compared with 34–44).

Mesocoelium danforthi , M. crossophorum and M. monodi are similar to these specimens by having the genital pore located from the midlevel of the esophagus to the level of the pharynx or more anterior, 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, and a posterior extent of the vitelline fields that terminate near to, or surpass the cecal ends posteriorly. Mesocoelium danforthi (24–32%) and M. monodi (33–56%) can be distinguished from these specimens from Panama by having the ceca occupying 24% or more of the postovarian space. In addition, M. monodi is a relatively large fluke (3,000 compared with less than 1,750 in both M. crossophorum and M. danforthi ), and it was originally described from central Africa rather than Central America or the Caribbean.

These specimens are consistent with M. crossophorum by having a similar ratio of the oral sucker width to the pharynx width (1:2.2 [1:2.0–1:2.3] compared with 1:2.6) and a similar ratio of the ventral sucker width to the oral sucker width (1:1.3 [1:1.2–1:1.4] compared with 1:1.4). There seems to be a difference in egg size in these specimens compared with M. crossophorum (33[29–36] by 21[18–23] compared with 41[36–45] by 27 [24–30]); however, as suggested by Dronen et al. (2012) the eggs of species of Mesocoelium are known to grow in the uterus and can be misleading when dealing with descriptions based on small sample sizes.

Figures

FIGURE 11. Mesocoelium crossophorum— USPNPC 0 92185.00 from Anolis biporcatus, ventral view of adult. FIGURE 12. Mesocoelium cf monodi— USNPC 0 90332.00 from Incilius valliceps, ventral view of adult.