Hyman, 1944
Overview
Diagnosis: Probursa veneris Hyman, 1944 may be recognized easily by (1) its auricles, (2) the copulatory bursa in front of the penis, (3) the ovaries being situated at the hind end of the pharyngeal pocket, (4) the vasa deferentia forming a meshwork underneath the copulatory bursa.
Habitus: Preserved specimens 1.15-1.70 mm long and 0.50-0.75 mm wide; according to Hyman (1944) animals may measure up to 3 mm in length. The body is elongate oval-shaped and has two small, laterally projecting, auricles. Hind and front end are rounded. In preserved specimens the body margins may be somewhat undulated, while the rounded hind end is delimited from the rest of the body by a slight constriction. The two eyes are situated at some distance from the anterior margin.
The body of preserved animals is brownish black, flecked and streaked (Hyman 1944), but living specimens appeared to be translucent white (Hyman 1952).
Alimentary System
The pharynx is about one-fifth to one-fourth of the body length. The inner circular muscle layer of the pharynx is slightly thicker than outer layer of circular muscles. The mouth opening lies at the proximal portion of the pharyngeal pouch, i.e. near the root of the pharynx.
The anterior ramus of the intestine extends anterior to the eyes. The posterior gut trunks unite behind the copulatory apparatus. The intestinal rami give off many branched lateral diverticula.
Male Reproductive System
The testes are few, i.e. about 7 to 9 on either side of the body. The large semicircular to oval-shaped follicles are situated between the proximal portions of the intestinal diverticula. The testes occur more or less in pairs. The follicles of the first pair lie close together, just behind the eyes and the brain, whereas the more posteriorly located pairs are spaced wider apart because of the presence of the pharynx. The testes extend from directly behind the brain up to the level of the copulatory bursa. The testicular follicles occupy most of the space between the dorsal and ventral body surfaces.
The vasa deferentia form a complex meshwork of convoluted tubules and vesicles just posterior to the hind end of the pharyngeal pocket and beneath the front end of the copulatory bursa. In sagittal sections it is clearly visible that this meshwork forms a sort of bulb over which extends the copulatory bursa. Although it could not be observed adequately, fusion of the vasa deferentia must take place in this bulb because behind it there is only a single, common vas deferens. This common vas deferens increases in diameter somewhat anterior to the penis bulb. After having entered the bulb, the common duct narrows immediately and, subsequently, opens at the tip of a small intrapenial papilla. This papilla, as well as the ejaculatory duct is lined with a densely staining, wavy and glandular epithelium.
The penis bulb is highly muscularized with more or less longitudinally running fibres. The male atrium is provided with a circular and a longitudinal muscle layer, both of which continue on the penis papilla.
Female Reproductive System
The rather large, rounded ovaries are situated on either side of the hind end of the pharyngeal pouch, medially to the ventral nerve cords. The oviducts arise from the postero-lateral surface of the ovaries, then pass over the ventral nerve cord and, subsequently, bifurcate, thus giving rise to an anteriorly and a posteriorly running branch. At about the level of the gonopore each posterior oviducal branch turns dorso-medially and penetrates the hind end of the bursal canal. The anterior oviducal branch extends forwards to about the brain and receives the openings of the numerous, well developed vitellaria.
The vitellaria are extensive, filling most of the space between the intestinal diverticula and between dorsal and ventral body surface; the follicles extend from the brain up to the level of the penis.
A large sac-shaped copulatory bursa is situated in front of the penis, i.e. between the penis bulb and the pharyngeal pocket. From its posterior surface arises the bursal canal which runs backwards along the dorsal surface of the penis bulb, and then widens gradually before communicating with the common atrium. The bursa is lined with a layer of tall, vesicular cells; sperm may be present in its lumen.
The bursal canal is surrounded by a well developed layer of circular muscles. Shell glands discharge into that part of the canal that lies posteriorly, i.e. ectally to the openings of the oviducts. Cement glands around the gonopore discharge their secretion to the exterior.
Eyes
The eye cups contain three retinal cells and lack a lens.
Reproduction
The cocoons are spherical and orange-coloured (Hyman 1952).
Ecology
Probursa veneris was found for the first time in empty shells of the clam Mercenaria (Hyman 1944), and later it was found on the red alga Mitophyllum medium (Hyman 1952).
Distribution
The species has been reported from Long Island, New York (Hyman 1944; Type locality: Fire Island, Long Island, New York) and from near Beaufort, North Carolina (Hyman 1952).
Material Examined
A.M.N.H.: Paratypes: no. 555, horizontal sections on on 2 slides; no. 556, horizontal sections on 1 slide; no. 558, sagittal sections on 1 slide.
A.M.N.H.: specimens collected near Beaufort, involving 2 whole mounts on 1 slide, 7 whole mounts on another slide, and sagittal sections on 1 slide.
A.M.N.H.: Holotype: no. 328, whole mount. Paratypes: nos. 329, 330, 331, 332, serial sections of one specimen on 4 slides; no. 551, 3 whole mounts, each on a separate slide; no. 552, serial sections of 1 specimen on 2 slides; no. 553, serial sections of 1 specimen on 2 slides; no. 554, serial sections of 1 specimen on 1 slide; no. 555, sections of 1 specimen on 2 slides; no. 556, no. 557, no. 558, serial sections of 1 specimen on each of the slides.
Type Material
A.M.N.H.: Holotype: no. 328, whole mount. Paratypes: nos. 329, 330, 331, 332, serial sections of one specimen on 4 slides; no. 551, 3 whole mounts, each on a separate slide; no. 552, serial sections of 1 specimen on 2 slides; no. 553, serial sections of 1 specimen on 2 slides; no. 554, serial sections of 1 specimen on 1 slide; no. 555, sections of 1 specimen on 2 slides; no. 556, no. 557, no. 558, serial sections of 1 specimen on each of the slides.