Mesocoelium americanum, Harwood, 1932

Dronen, Norman O., Calhoun, Dana M. & Simcik, Steven R., 2012, Mesocoelium Odhner, 1901 (Digenea: Mesocoelidae) revisited; a revision of the family and re-evaluation of species composition in the genus 3387, Zootaxa 3387 (1), pp. 1-96 : 78-79

Mesocoelium americanum

( Figure 38; Table 18)

Definitive host: Hyla cinerea (Schnieder) , green treefrog ( Anura : Hylidea)

Locality: Burleson County, Texas, USA, 30° 24’ N, 96° 13’ W .

Site: Intestine.

Deposited specimens: Voucher specimens USNPC 104823.00.

Description of specimens: Based on 10 adult specimens. With characteristics of genus. Body monas type, small with slightly rounded posterior end, 1,568 (1,288 –1,875) by 703 (650– 775); no body spines observed; forebody 547 (450–630) long, 33–37% of body length. Mouth subterminal; oral sucker spherical, 228 (215–240) by 221 (200–240); prepharynx short; pharynx wider than long, 69 (65–73) by 95 (88–104); esophagus longer than prepharynx, 60 (44–73) long; cecal bifurcation ¾ distance down forebody; ceca reaching well posterior to ovary, terminating about ½ distance down the postovarian space, occupying 34–38% of length of postovarian space. Ratio of widths of oral sucker and pharynx 1:2.3 (1:2.1–1:2.5). Ventral sucker located 1/3 to 1/2 down body, smaller than oral sucker, 172 (159–185) by 167 (153–177). Ratio of sucker widths 1:1.3 (1: 1.2–1:1.4).

Testes smooth, side by side to slightly diagonal, situated at upper ½ of ventral sucker. Right testis 159 (135–187) by 144 (109–174); left testis 153 (32–182) by 133 (122–146). Cirrus sac medial, situated between cecal bifurcation and ventral sucker, enclosing short cirrus, reduced par prostatica, short to medium ejaculatory duct surrounded by prostate cells and bipartite seminal vesicle, 143 (119–182, 8–10% of body length) by 44 (41–47). Genital pore immediately anterior to cecal bifurcation, distinctly submedian.

Ovary smooth, posttesticular, situated immediately posterior to right or left testis, 137 (111–143) by 125 (117–132), removed from posterior end by some distance; postovarian space 798 (670–970) long, 51–52% of body length. Seminal receptacle spherical, located immediately sinistral to ovary. Laurer’s canal present, opening not observed. Vitelline fields distributed along ceca from posterior margin of oral sucker posteriorly to midlevel of hindbody, terminating near to, or surpassing cecal ends; vitelline follicles 49 (22–65) by 43 (28–80). Uterus occupies most of hindbody, largely postacetabular. Eggs operculate, 38 (35–43) by 23 (20–26) (n = 30).

Excretory vesicle Y-shaped; excretory pore terminal.

Remarks: These specimens (USNPC 104823.00) have an unusual body shape (likely due to fixation) but have moderately long ceca, and a genital pore that is prebifurcal and submedian, placing them in the monas body type. The posterior extent of the vitelline fields terminate near to, or surpass the cecal ends posteriorly; the gonads overlap the area of the ventral sucker; the body is oval, widest near midbody; the genital pore is located posterior to the midlevel of the esophagus, just above the cecal bifurcation; the ceca terminate near the midlevel of the postovarian space, occupying 34–38% of the postovarian space and the anterior extent of the vitelline fields reach anteriorly to the level of the oral sucker, placing them in M. americanum . These specimens are relatively short (1,288 –1,875), but conform to M. americanum in all other respects ( Table 18). These specimens were collected from a frog rather than a skink or snake, and it is possible that differences such as growth and development may be host-induced.