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 : 3

Mesocoelium meggitti— USNPC 0 92800.00

( Figure 1 , Table 1)

Host: Anolis lionotus (Cope) , lion anole ( Squamata : Polychrotidae ).

Locality: Panama. (Native)

Description: Based on two specimens (one intact and one somewhat distorted): Body 1,846 by 520; forebody 340 long, representing 18% of body length. Mouth subterminal; oral sucker circular, 160 by 160; prepharynx short; pharynx 52 by 62; ratio of pharynx width to oral sucker width 1:2.4; esophagus 21 long; ceca terminating posterior to posterior margin of ovary, occupying at least 20% of postovarian space (cecal ends not visible). Ventral sucker longer than wide, situated in anterior 1/3 of body, 135 by 133; ratio of ventral sucker width to oral sucker width 1:1.2. Testes opposite; left testis 159 by 135; right testis 143 by 122. Genital pore median, located immediately posterior to posterior margin of pharynx. Cirrus sac clavate, 143 long, representing 8% of body length. Ovary oval, 117 by 143; postovarian space 1,170 long, representing 63% 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 posteriorly. Eggs 31 (27–35) by 22 (21–23). Excretory system not visible.

Remarks: Both specimens appeared to be contracted and their bodies rolled to one side. The oral sucker has been pulled away from the anterior end of the body, the pharynx has been tilted to the right and the esophagus has become constricted. Additionally, the gonads have become shifted right and pulled into a tight, overlapping cluster at the level of the ventral sucker. The poor quality of these specimens precluded observation of some structures (e.g. ceca termination and bladder).

Although these specimens have ceca that surpass the ovary posteriorly and a prebifurcal genital pore, the genital pore is median rather than submedian, precluding their assignment to the monas body type. Based on these characters, these specimens are assigned to the mesembrinum body type. In addition, M. monas as originally described and redescribed has vitelline fields that terminate well short of cecal ends (the level of the anterior margin of the ovary) as compared with having vitelline fields that surpass the cecal ends, as is the case in USNPC 0 92800.00. These specimens further differ from M. monas by having a narrower oral sucker (160 compared with 382), a narrower pharynx (62 compared with 138), a narrower ventral sucker (133 compared with 344), and a shorter maximum egg length (35 compared with 44).

These specimens are consistent with M. meggitti by having gonads that overlap the area of the ventral sucker, genital pore located at the level of the anterior 1/2 of the esophagus, a similar ratio of the ventral sucker width to the oral sucker width (1:1.2 compared with 1:1.5), a similar ratio of the pharynx width to the oral sucker width (1:2.4 compared with 1:2.0), a similar length of the postovarian space (1,170; 63% of body length compared with 880; 52%), and the genital pore in these specimens is median, as is the case in M. meggitti . There were slight differences in egg length and width seen between the specimens and M. meggitti (27–35 by 21–23 compared with 34–37 by 23–26), but the eggs of species of Mesocoelium are known to grow in the uterus once produced ( Dronen et al. 2012), and we only measured normally appearing eggs from the distal end of the uterus, which yielded smaller ranges. In one of the specimens from USNPC 0 92800.00, the forebody was rolled to one side moving the esophagus and pharynx to the left, so that the genital pore artificially appeared to be slightly submedian.

Figures

FIGURE 1. Mesocoelium meggitti— USNPC 0 92800.00 from Anolis lionotus, ventral view of adult.