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 : 24-25

Mesocoelium cf lanceatum— USNPC 0 84288.00

( Figure 14 ; Table 4 )

Host: Anaxyrus americanus (Frost) (syn. Bufo americanus Holbrook ), American toad ( Anura : Bufonidae ).

Locality: Arkansas, USA. (Native)

Description: Based on one specimen: Body 1,250 by 470; forebody 373 long, representing 30% of body length. Mouth subterminal; oral sucker subspherical, 153 by 161; prepharynx absent; pharynx subspherical, 50 by 48; ratio of pharynx width to oral sucker width 1:3.4; esophagus 75 long; ceca short, terminating anterior to anterior margin of ovary. Ventral sucker subspherical, situated anterior 1/3 of body, 123 by 115; ratio of ventral sucker width to oral sucker width 1:1.4. Testes subspherical, oblique; right testis 100 by 125; left testis 125 by 100. Genital pore postbifurcal, median. Cirrus sac, 150 long, representing 12% of body length. Ovary spherical, 105 by 110; postovarian space, 620 long, representing 50% of body length. Uterus extensive, filling hindbody. Vitelline follicles distributed in lateral fields from level of pharynx to level of posterior margin of ovary. Eggs 45 (44–45) by 30 (29–30). Excretory system not visible.

Remarks: The edges of this specimen are convoluted and folded on the right side, suggesting it may have been fixed without coverslip pressure and/or heat. The body also is twisted at the level of the gonads, and the cirrus sac and right testis are displaced to the left, so that the right testis is located immediately anterior to the right testis.

This specimen cannot be assigned to M. monas because it has a postbifurcal genital pore, the vitelline fields terminate at, or posterior to the posterior margin of the ovary and the ceca do not surpass the ovary posteriorly, whereas in M. monas the vitelline fields do not surpass the ovary posteriorly and the ceca surpass the ovary posteriorly (occupying 31% of postovarian space). This specimen; however, can be assigned to the lanceatum body type because it has short ceca that do not surpass the ovary and it has a postbifurcal genital pore.

This specimen further differs from M. monas by a shorter body (1,250 compared with 1,835 [1,260–2,410]), a narrower ventral sucker (115 compared with 344), larger eggs (45 [44–45] by 30 [29–30] compared with 39 [34–44] by 23 [21–25]), and a larger ratio of oral sucker width to the pharynx width (1:3.4 compared with 1:2.6).

This specimen is consistent with M. lanceatum by having a similar ratio of ventral sucker width to oral sucker width (1:1.4 compared with 1:1.6 [1:1.6–1:1.7]), and similar eggs (45 [44–45] by 30 [29–30] compared with 42 [40–44] by 25 [23–27]). This specimen differs from M. lanceatum by having a shorter body length (1,250 compared with 2,700 [2,100–3,300]) and a shorter postovarian space (620 compared with 1,728). Mesocoelium lanceatum was originally described from Japan and to our knowledge there has not been a species of Mesocoelium described from the Americas that has short ceca. Although this specimen may represent an undescribed species, it is possible that an Old World species may have been introduced into Anaxyrus (Bufo) americanus in Arkansas.

Figures

FIGURE 14. Mesocoelium cf lanceatum— USNPC 0 84288.00 from Anaxyrus americanus, ventral view of adult.

Tables

TABLE 4. Comparative measurements, morphometric percentages and morphometric ratios for species of Mesocoelium previously identified as Mesocoelium monas that appear to be Mesocoelium burti, Mesocoelium lanceatum or Mesocoelium pesteri from the Natural History Museum, UK and the United States Parasitology Collections.

Characteristic	M. burti NHMUK 1980.11.12 4 n=5	M. cf lanceatum USNPC 0 84288.00 n=1	M. cf pesteri USNPC 0 89067.00 n=2
Body length	1,378 (1,274–1,482)	1,250	923 (806–1,040)
Forebody length	430 (410–450)	373	245
Forebody length as a percentage of body length	31% (30–32%)	30%	27%
Oral sucker width	228 (216–240)	161	246 (216–276)
Pharynx width	81 (78–83)	48	NM
Oral sucker width/pharynx width	1:2.8 (1:2.6–1:3.0)	1:3.4	NM
Ventral sucker width	167 (156–177)	115	153 (120–182)