Mesocoelium brevicaecum, Ochi, 1929

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 : 39

Mesocoelium brevicaecum

( Figures 1–3 ; Table 13)

Definitive hosts: Duttaphrynus melanostictus (Schneider) , (syn. Bufo melanostictus Schneider ),

the common Indian or Asiatic toad ( Anura : Bufonidae ).

Locality: Taiwan.

Site: Intestine.

Specimens examined: BMNH 1973.5.24.

Description of specimens: Based on 13 specimens. With characteristics of genus. Body lanceatum type, small, elongate with somewhat tapered posterior end, spinose, mean 2,150 (range 1,663 –2,488) by 646 (550–860); body spines 18–22 long; forebody 549 (410–765) long, 23–32% of body length. Mouth subterminal; oral sucker spherical to subspherical, 231 (195–265) by 235 (185–275); prepharynx short, nearly absent; pharynx spherical to subspherical, 90 (60–125) by 86 (75–113); esophagus 64 (40–125) long; cecal bifurcation near midlevel of forebody; ceca short, terminating anterior to level of ovary. Ratio of widths of oral sucker and pharynx 1:2.5 (1:2.0–1:2.7). Ventral sucker located in anterior ½ of body, smaller than oral sucker, 191 (138–220) by 185 (129–210). Ratio of sucker widths 1:1.3 (1:1.2–1:1.4).

Testes smooth, side by side to slightly diagonal, situated at level of ventral sucker. Right testis 190 (110–260) by 174 (120–220); left testis 185 (119–220) by 175 (118–220). Cirrus sac situated between cecal bifurcation and ventral sucker, enclosing short cirrus, reduced pars prostatica, short ejaculatory duct surrounded by prostate cells, and bipartite seminal vesicle, 187 (125–250, 8–10% of body length) by 73 (53–90). Genital pore immediately postbifurcal, median.

Ovary smooth, posttesticular, situated immediately posterior to right or left testis, 207 (165–230) by 200 (150–235), removed from posterior end by some distance; postovarian space 1,239 (975–1,400) long, 52–62% of body length. Ratio of width of ovary to mean width of testes 1:0.9 (1:0.7–1:1.1). Seminal receptacle spherical, located immediately sinistral and slightly posterior to ovary. Laurer’s canal present, opening on dorsal body surface. Vitelline fields distributed along ceca from level of oral sucker posteriorly to level of ventral sucker, terminating anterior to cecal ends; vitelline follicles 60 (40–130) by 50 (30–90) (n = 30). Uterus largely postacetabular, filling most of hindbody. Eggs operculate, 43 (40–46) by 23 (20–28) (n = 40).

Excretory vesicle Y-shaped, with poorly developed arms; excretory pore slightly subterminal.

Remarks: These specimens (BMNH 1973.5.24) have short ceca, and a genital pore that is postbifurcal and median, placing them in the lanceatum body type. Eggs are larger than 30 by 18 (40–46 by 20–26) and specimens have a ratio of the width of the pharynx to the width of the oral sucker of less than (1:2.0–1:2.7), and therefore are assigned to M. brevicaecum . Although the large ranges of egg measurements reported in the original descriptions of the species synonymized with M. brevicaecum in the current study ( M. magniovum , M. micreatum , M. minutum and M. tritoni ) may be somewhat suggestive of the possibility of multiple species within M. brevicaecum as we propose it herein, the extensive overlap between the ranges of these egg measurements makes separation of M. brevicaecum into additional species using egg length and width impractical. The other distinguishing characteristics of the species synonymized herein with M. brevicaecum are nearly identical and all five species were originally described from the same general geographical region (Table 3). It is our belief that the question of the distinctiveness of M. brevicaecum as proposed herein can only be resolved by morphological and/or molecular examination of additional specimens from the type hosts from the type locality of the original species.

Figures

FIGURES 1–3. Mesocoelium brevicaecum (BMNH 1973.5.25.1-11). 1. Ventral view of adult. 2. Composite drawing of area between cecal bifurcation and ventral sucker showing placement of genital pore, uterus and seminal vesicle, ventral view. 3. Composite drawing of area of oötype, ventral view. Abbreviation used in figures: C=cecum; E=egg; Ev=excretory vesicle; G= genital pore; L= Laurer’s canal; M=Mehlis’ glands; OV=ovary; P=pharynx; SR= seminal receptacle; SV=seminal vesicle; T=testis; U=uterus; VD=vitelline duct.