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 : 75-78

Mesocoelium americanum

( Figures 35–37 ; Table 18)

Type host: Stoveria dekayi texana (Holbrook), Texas brown snake ( Squamata : Colubridae )

Additional host: Leiolopisma laterale (Say) , common ground skink ( Squamata : Scincidae ).

Type locality: Houston , Texas, USA, 29° 28’ N, 91° 35’ W .

Site: Intestine.

Specimens examined: Holotype USNPC 030868.00 ; Paratype USNPC 030869 .00.

num from different geographical localities and definitive hosts.

n = Sample size.

Redescription: Based on type material. With characteristics of genus. Body monas type, small, elongate with somewhat tapered posterior end, spinose, holotype 1,325 (range 1,325 –4,038; mean 2,682) by 513 (513–1,238; 878); body spines 10–13 long; forebody 400 (400–950; 675) long, 24–30% of body length. Mouth slightly subterminal; oral sucker spherical to sub spherical, 210 (210–380; 295) by 208 (208–360; 284); prepharynx short; pharynx wider than long, 63 (52–63; 57) by 85 (85–165; 125); esophagus longer than prepharynx, 25 (25–160; 93) long; cecal bifurcation ¾ distance down forebody; ceca reaching well posterior to ovary, occupying 26% (26–26%; 26%) of postovarian space. Ratio of widths of oral sucker and pharynx 1:2.4 (1:2.2–1:2.4; 1:2.3). Ventral sucker located ⅓ distance down body, smaller than oral sucker, 125 (125–255; 190) by 125 (125–238; 182). Ratio of sucker widths 1:1.7 (1:1.5–1:1.7; 1:1.7).

Testes smooth, side by side to slightly diagonal, situated at level of upper ⅓ of ventral sucker. Right testis 70 (70–250; 160) by 103 (103–220; 162); left testis 85 (85–280; 183) by 90 (90–190; 140). Cirrus sac medial, situated between cecal bifurcation and ventral sucker, enclosing short cirrus, reduced pars prostatica, short ejaculatory duct surrounded by prostate cells, and bipartite seminal vesicle, 113 (113–238; 176, 6–9% of body length) by 50 (50–75; 63). Genital pore immediately prebifurcal submedian.

Ovary smooth, posttesticular, situated immediately posterior to right testis, 118 (118–210; 164) by 95 (95–255;175), removed from posterior end by some distance; postovarian space 740 (740 –2,625; 1,683) long, 56–65% 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 oral sucker posteriorly to near the midlevel of hindbody, terminating near to, or surpassing cecal ends; vitelline follicles 23–48 (23–105; 50) by 18–23 (18–100; 49) (n = 20). Uterus largely postacetabular, filling most of hindbody. Eggs operculate, 39–44 (36–44; 43) by 23–26 (21–26; 24) (n = 40).

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

Remarks: These specimens (USNPC 030868.00, 030869.00) 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 midlevel of hindbody, occupying 26% 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 . In our examination of the holotype and paratypes of M. americanum , we observed that a number of our measurements of structures were outside of the ranges given in the original description (e.g. the body length of the paratype was 4,038, which is much larger than the upper size limit of 2,000 reported in the original description by Harwood 1932; the length of the cirrus sac was 113–238 compared to 150). Given these circumstances we felt that the species should be redescribed using the type and paratype specimens ( Table 18). It should be noted that the holotype appears to be poorly fixed, the forebody is somewhat contracted, the tegument is damaged, it is apparently a young adult (small body with few eggs; 180– 200 eggs) and that both the holotype and the paratype appear to be coated with a layer of small bubbles or blisters. No body spines were seen on the holotype, but there were a few body spines present on the paratype. The female reproductive system of the paratype is exceptionally clear and shows clearly all the pertinent structures. Mesocoelium americanum is similar to M. danforthi in most respects and are found in the same general geographical area; however, the immediate prebifurcal placement of the genital pore in M. americanum distinquishes it from M. danforthi .

Figures

FIGURES 35–37. Mesocoelium americanum (USNPC 0.30869.00). 35. Ventral view of paratype. 36. Drawing of seminal vesicle. 37. Drawing of area of oötype, ventral view.