Mesocoelium thapari, Gupta & Jahan, 1976

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 : 83-86

Mesocoelium thapari

( Figure 44 ; Table 16)

Definitive host: Pangasius micronemus (Bleeker) , shortbarbel pangasius (Suluriformes: Pangasiidae ).

Locality: Malaysia.

Site: Intestine.

Specimens examined: Voucher specimens BMNH 1983.4.25.

Description of specimens. Based on two adult specimens. With characteristics of genus. Body leiperi type, relatively large, elongate with slightly rounded ends, 3,544 (3,513 –3,575) by 1,013 (925–1,100); no body spines observed; forebody 888 (840–935) long, 23–27% of body length. Mouth subterminal; oral sucker spherical to subspherical, 278 (275–280) by 288 (255–320); prepharynx short; pharynx wider than long, 92 (88–95) by 94 (77–110); esophagus longer than prepharynx, 140 (110–170) long; cecal bifurcation ⅓ distance down forebody; ceca reaching well posterior to ovary, terminating about ¾ distance down hindbody, occupying 58–62% of length of postovarian space. Ratio of widths of oral sucker and pharynx 1:3.1 (1:2.9–1:3.3). Ventral sucker located upper ⅓ down body, smaller than oral sucker, 228 (205–250) by 225 (220–230). Ratio of sucker widths 1:1.3 (1: 1.1–1:1.5).

Testes smooth, nearly side by side to slightly diagonal, overlapping posterior ½ of ventral sucker. Right testis 173 (170–175) by 158 (130–184); left testis 174 (145–203) by 144 (118–183). Cirrus sac medial, situated immediately postbifurcal, well anterior to ventral sucker, enclosing short cirrus, reduced par prostatica, short to medium ejaculatory duct surrounded by prostate cells and bipartite seminal vesicle, 237 (223–250, 6–7% of body length) by 60 (50–70). Genital pore postbifurcal, median.

Ovary smooth, posttesticular, situated immediately posterior to right or left testis, 130 (120–140) by 132 (120–143), removed from posterior end by some distance; postovarian space 2,163 (2,075 –2,250) long, 59–63% of body length. Seminal receptacle spherical, located immediately sinistral to ovary. Laurer’s canal present, opening not observed. Vitelline fields distributed along ceca from level of esophagus posteriorly to midlevel of postovarian space or more posterior, terminating a short distance anterior to cecal ends; vitelline follicles delicate (poorly developed), sparsely scattered along ceca, 39 (30–60) by 41 (22–90). Uterus occupies most of hindbody, largely postacetabular. Eggs operculate, 37 (36–39) by 22 (20–23) (n = 25).

Excretory vesicle Y-shaped; excretory pore terminal.

Remarks: These specimens (BMNH 1983.4.25) have moderately long ceca, and a genital pore that is postbifurcal and median, placing them in the leiperi body type. The posterior extent of the vitelline fields terminate well anterior to the cecal ends (about ¾ of the cecal length); the ceca are unusually long, occupying 59–63% of the length of the postovarian space and there are few, delicate, sparsely scattered vitelline follicles present, placing these specimens in M. thapari . These specimens are somewhat larger than those reported by Gupta & Jahan (1976) in the original description of this species (3,513 –3,575 long compared to 2,430 –2,800), have a smaller egg (36–39 long compared to 40–50) and are from a catfish rather than a frog, but correspond in all other respects to M. thapari (Table 16). It is possible that these specimens represent an undescribed species, but without additional specimens we feel the appearance and distribution of the vitelline follicles and similarities in measurements warrant their preliminary assignment to M. thapari . Both are from the same general geographic region of the Old world ( Malaysia and India, respectively).

Figures

FIGURES 44–45. Mesocoelium thapari (BMNH 1984.4.25.11-12) and Mesocoelium neohylae n. sp. (USNPC 104821.00). 44. Mesocoelium thapari; Ventral view of adult. 45. Mesocoelium neohylae n. sp.; Ventral view of holotype.