Mesocoelium danforthi, Hoffman, 1935

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 : 66

Mesocoelium danforthi

( Figure 27 ; Table 17)

Type host: Diplodiscus pleii Duméril & Bibron (syn. Celestus pleii [Duméril & Bibron]), Puerto Rican galliwasp or 4-legged snake ( Squamata : Aguidae).

Type locality: El Yunque National Forest , formerly Luquillo National Forest, Puerto Rica, USA, 18° 19’ N, 65° 47’ W .

Site: Intestine.

Specimens examined: Holotype USNPC 039570.00 ; Paratypes (2) USNPC 039571 .00.

Redescription: Based on type material. With characteristics of genus. Body monas type, small, elongate with somewhat tapered posterior end, spinose, holotype 1,680 (range 1,325 –1,750; mean 1,585) by 550 (365–550; 458), body spines found on one paratype only, 4–5 long; forebody 550 (365–550; 457) long, 33% (27–33%; 30%) of body length. Mouth slightly subterminal; oral sucker longer than wide, 340 (330–350; 340) by 315 (300–320; 312); prepharynx short; pharynx wider than long, 88 (83–95; 89) by 113 (100–113; 105); esophagus 25 (25–88; 57) long; cecal bifurcation about ½ distance down forebody; ceca reaching well posterior to ovary, occupying 24% (24–32%; 28%) of postovarian space. Ratio of widths of oral sucker and pharynx 1:2.8 (1:2.9–1:3.2; 1:3.1). Ventral sucker located ⅓ distance down body, smaller than oral sucker, 170 (160-188; 169) by 173 (160–188; 172). Ratio of sucker widths 1:1.8 (1:1.7–1:1.9; 1:1.8).

Testes smooth, side by side to diagonal, situated at level of ventral sucker. Right testis 98 (93–98; 95) by 118 (106–118; 113); left testis 113 (83–118; 102) by 100 (98–116; 104). 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, 130 (130–153; 142, 8–9% of body length) by 50 (40–50; 50). Genital pore prebifurcal, immediately postpharyngeal, submedian.

Ovary smooth, posttesticular, situated immediately posterior to left testis, 111 (100–120) by 140 (no range), removed from posterior end by some distance; postovarian space 910 (680–915; 768) long, 51– 54% of body length. Seminal receptacle spherical, located immediately dextral to ovary. Laurer’s canal present, opening not observed. Vitelline fields distributed along ceca from level of oral sucker posteriorly to near midlevel of hindbody, terminating some distance posterior to cecal ends; vitelline follicles 15–53 (15–75; 52) by 15–40 (13–40; 24) (n = 20). Uterus largely postacetabular, filling most of hindbody. Eggs operculate, 33–38 (32–38; 35) by 20–23 (20–24; 22) (n = 40).

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

Remarks: These specimens (USNPC 039570.00, 039571.00) appear to be contracted, 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 near the posterior margin of the pharynx (based on the original description); the ceca are moderately long, terminating near midlevel of postovarian space and occupying 24–32% of postovarian space; and the maximum egg size is 38 by 24, placing it in M. danforthi . In our examination of the holotype and paratypes of M. danforthi 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 was 1,325 –1,750 compared to a reported range of 1,131 –1,650; the diameter of the ventral sucker was 160–188 compared to 148–172; the length of the cirrus sac was 130–153 compared to 146; the width of the testes were 98–116 compared to 104–116). In addition, the original description by Hoffman (1935) omitted a number of measurements (e.g. length of forebody; length of postovarian space; egg size) and morphometric ratios were not given. Although this species was redescribed by Confrêsi-sala (1964), we felt that the type specimens should be reevaluated (Table 17). It should be noted that the holotype and paratypes are coated with a layer of small bubbles and appear to be contracted, which has moved the cecal bifurcation anterior towards the oral sucker giving the impression that there is no esophagus, and that the genital pore has been displaced slightly anterior giving the impression that it opens slightly more anterior than would be its normal placement. The “membrane” covering the opening to the oral sucker “with a longitudinal median slit” previously reported for this species was not evident in these specimens; however, the mouth of the oral sucker is rotated anteriorly so that the mouth appears to be almost terminal.

Figures

FIGURE 27. Mesocoelium danforthi (USNPC 039570.00). 27. Ventral view of type specimen.