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 : 7

Mesocoelium meggitti— NHMUK 1977.9.28 6

( Figure 3 , Table 1)

Host: Trachylepis quinquetaeniata ( Lichtenstein) (syn. Mabuya quinquetaeniata Lichtenstein ) five-lined mabuya ( Squamata : Scincidae ).

Locality: Rhodesia. (Native)

Description: Based on three specimens (two intact and one broken): Body 1,924 (1,352–2,496) by 537 (416–702); forebody 645 (560–730), representing 34% of body length. Mouth nearly terminal; oral sucker oval, 139 (47–230) by 220 (210–230); prepharynx short; pharynx oval, 77 (73–80) by 148 (86–210); ratio of width of pharynx to width of oral sucker 1:2.3 (1:2.1–1:2.4); esophagus 107 (0–213) long; ceca terminating well past posterior margin of ovary, occupying 38% of postovarian space. Ventral sucker oval, situated near posterior margin of anterior 1/3 distance of body, 179 (130–227) by 155 (133–177); ratio of ventral sucker width to oral sucker width 1:1.5 (1.3–1.6). Testes opposite or slightly oblique; right testis 138 (107–169) by 132 (125–139); left testis 136 (107–164) by 165 (156–174). Genital pore median, located immediately anterior to midlevel of esophagus. Cirrus sac 140 long, representing 7% of body length (n=1). Cirrus sac 140 long, representing 7% of body length. Ovary oval, 124 (104–143) by 122 (104–140); postovarian space 1,031 (580–1,482) long, representing 54% of body length. Uterus extensive, filling hindbody. Vitelline follicles distributed in lateral fields from midlevel of oral sucker to level of cecal ends, or slightly more posterior. Eggs 34 (29–39) by 21(16–26). Excretory system not visible.

Remarks: One specimen (far left on slide) is clearly more fully developed (likely older) than the others, as indicated by having a larger body size, a longer, more developed postovarian space and noticeably more fully developed eggs in the uterus compared with the two other specimens. A limited number of structures could be observed in one specimen because the body was twisted causing the tegument to rupture, allowing the ovary and other organelles to protrude out of the body.

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. These specimens further differ from M. monas by having vitelline fields that surpass the cecal ends posteriorly rather than terminating well short of the cecal ends, a narrower oral sucker (210–230 compared with 382), and a narrower ventral sucker (133–177 compared with 344).

These specimens are consistent with M. meggitti by having a prebifurcal genital pore that opens anterior to the midlevel of esophagus, a similar ratio of ventral sucker width to oral sucker width (1:1.3–1:1.6 compared with 1:1.5), a similar ratio of pharynx width to oral sucker width (1:2.1–1:2.4 compared with 1:2.0), a similar body size (1,924 [1,352–2,496] compared with 1,590 [1,070–2,110]), a similar postovarian space length (580–1,482 compared with 880), and similar sized eggs (34 [29–39] by 21[16–26] compared with 36 [34–37] by 24 [23–26]). Based on the redescription by Dronen et al. (2012), there are some slight differences in the percentage that the ceca surpass the ovary into the postovarian space (38% compared with greater than 28%) and in the ventral sucker width (155 [133–177] compared with 220 [220–240]) when comparing these specimens to M. meggitti .

Figures

FIGURE 3. Mesocoelium meggitti— NHMUK 1977.9. 28 6 from Trachylepis guinguetaeniata, ventral view of adult. FIGURE 4. Mesocoelium meggitti— NHMUK 1980.11. 12 1 - 3 from Bufo marinus, ventral view of adult.