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Ball, 1977

Overview
Diagnosis: Tryssosoma jennyae Ball, 1977 can be recognized by the following combination of features: (1) pre-pharyngeal, ventral testes; (2) oviducts opening separately into bursal canal; (3) vasa deferentia uniting to form a common vas deferens just within the penis bulb; (4) presence of a copulatory bursa.
Habitus: According to Ball (1977a) preserved animals are up to 3.25 mm long and 1.5 mm wide, and he described the dorsal surface as "pale streaky brown"; the ventral surface is pale. In preserved specimens the body margins run parallel; the front end is broadly rounded and the hind end very blunt.

Alimentary System
The large pharynx is between one-third and one-half of the body length, its root being situated somewhat anteriorly to the middle of the body. The inner circular muscle layer of the pharynx is much thicker than the outer circular muscle layer. The mouth opening is situated at the hind end of the pharyngeal cavity.
The anterior intestinal ramus extends anterior to the eyes without giving rise to pre-ocellar diverticula. This gut trunk gives rise to about 5 pairs of branched, postocellar lateral diverticula. The posterior intestinal rami meet in the hind end of the body, posteriorly to the copulatory apparatus.

Male Reproductive System
The testes are situated ventrally and extend from directly behind the ovaries to the root of the pharynx. There are about 7-9 follicles on either side of the anterior intestinal ramus (Ball 1977a).
The vasa deferentia form well developed ducts already at about the level of the root of the pharynx. Behind the pharyngeal pouch the ducts curve dorso-medially, meanwhile decreasing in diameter, and, subsequently, recurve towards the front end. At the level of the penis bulb the vasa deferentia curve again towards the hind end of the body and penetrate, separately, the dorsal surface of the penis bulb. Immediately after having entered the bulb, the ducts unite to form a common vas deferens. This vas deferens is lined with a cuboidal, nucleate epithelium and communicates with a spacious seminal vesicle, the latter gradually narrowing to form the ejaculatory duct. Seminal vesicle and ejaculatory duct are lined with an infranucleate epithelium which is pierced by the numerous openings of penis glands.
The muscular hemi-spherical penis bulb is well-developed; the penis papilla is a relatively small and blunt cone with a vertical or somewhat oblique orientation. The rather spacious male atrium is lined with a papillate, nucleate epithelium which is underlain by a well developed layer of circular muscles and an equally well developed layer of longitudinal muscle fibres, respectively. These muscle layers extend on the penis papilla.

Female Reproductive System
The paired ovaries are situated directly behind the brain, medially to the ventral nerve cords. The oviducts arise from the lateral surface of the ovaries and run laterally to the nerve cords. Behind the gonopore the oviducts curve medially and open, separately, into the bursal canal.
The latter arises from the antero-ventral surface of the sac-shaped copulatory bursa, which is lined with large vacuolated and nucleate cells. The bursal canal widens ectally to the openings of the oviducts and this enlarged section receives the secretion of well-developed shell glands. The canal is lined with a papillate, infranucleate epithelium which bears cilia; it is surrounded by a well-developed subepithelial layer of circular muscles and a somewhat thinner layer of longitudinal muscles.
The vitellaria are extensive, extending from immediately anterior to the ovaries into the hind end of the body and, in general, occupying the entire space between dorsal and ventral body surface. Anterior to the pharynx the main body of vitellaria is situated laterally to the testes.

Eyes
Each eye cup contains three retinal cells and a rounded or ellipsoid lens.

Ecology
The type specimens of T. jennyae were collected from the "milieu hypothelminorhique" (phreatic or perched water tables) on St. Helena, representing the only known sample localities of the species sofar. The perched water table system is a complex type of habitat, consisting of pools of freshwater, at some elevation, from which water percolates through the rock and collects in shallow depressions at lower elevations. Several specimens of T. jennyae were collected from such a habitat on Peak Hill, at an elevation of 1400 ft (427 m).

Distribution
Type locality: Phreatic water tables on St. Helena. The species is known only from the type locality.

Material Examined
M.R.A.C.: Paratypes: 33.345, sagittal sections on 1 slide; 35.384, transverse sections on 4 slides; 35.386, whole mount on 1 slide; 35.380, sagittal sections on 2 slides; 35.381, sagittal sections on 2 slides; 35.382, sagittal sections on 2 slides; 35.383, transverse sections on 3 slides; 33.346, sagittal sections on 1 slide; 33.346, sagittal sections on 2 slides; 35.379, sagittal sections on 3 slides.
Private collection I. R. Ball: paratype 33.929-2, sagittal sections on 2 slides.

Type Material
M.R.A.C.: Holotype: MT 33.928, April 1967, sagittal sections on 1 slide. Paratypes: 33.345, sagittal sections on 1 slide; 35.384, transverse sections on 4 slides; 35.386, whole mount on 1 slide; 35.380, sagittal sections on 2 slides; 35.381, sagittal sections on 2 slides; 35.382, sagittal sections on 2 slides; 35.383, transverse sections on 3 slides; 33.346, sagittal sections on 1 slide; 33.346, sagittal sections on 2 slides; 35.379, sagittal sections on 3 slides.
Private collection I. R. Ball: paratype 33.929-2, sagittal sections on 2 slides.

Tryssosoma jennyae