Diagnosis: Miroplana trifasciata Kato, 1931 can be recognized easily by (1) the three black bands across the body, (2) the two eyes which are very wide apart, (3) two pairs of testes, (4) an eversible penis provided with spines, (5) a bifurcated bursal canal.
Habitus: Fully extended live specimens are 1-2 mm long and 0.2-0.5 mm wide. The animals are of an elongate-oval shape with the anterior body margin broadly rounded and the hind end of the body obtusely pointed. Three black bands run across the dorsal body surface, which shows a light pink ground colour. These dark bands are composed of a densely reticulated pattern, resulting from the accumulation of dark pigment granules, which lie embedded in the parenchyma just beneath the epidermis. The two eyes lie in the frontal black band and are spaced very wide apart, each of them being very close to the lateral body margin.
The pharynx is situated in the anterior portion of the body and measures between one-fourth and one-third of the body length. The root of the pharynx is at about the posterior margin of the anterior cross band, whereas its tip lies at about the middle of the body. The mouth opening is at the hind end of the pharyngeal pocket.
As a consequence of this anterior position of the pharynx, the anterior ramus of the intestine is short and gives off only a pair of preocellar diverticula. From each posterior ramus arise about 14 lateral diverticula. Behind the copulatory apparatus the posterior rami also give rise to about 4 pairs of median diverticula, which are connected, thus forming commissures between the two posterior gut trunks.
Male Reproductive System
There are two pairs of large testes. The follicles of the first pair lie on either side of the anterior gut trunk, between the brain and the root of the pharynx. The second pair of testicular follicles is situated at about the posterior fourth of the pharynx. These last-mentioned testes communicate, through narrow ducts, with the much broader vasa deferentia which arise from the anterior pair of testes. After having pierced the penis bulb, the vasa deferentia open into a rounded seminal vesicle which tapers to the ejaculatory duct, the latter opening at the tip of the penis papilla. Seminal vesicle and ejaculatory duct are lined with a cuboidal, nucleate epithelium. The distal section of the ejaculatory duct is provided with a number of slightly curved spines, being 3-5 um long. This distal portion of the ejaculatory duct is eversible, so that on occasions these spines occur along the outside of the penis (see Fig. 176). Numerous penis glands are distributed in the parenchyma around the penis bulb and discharge their secretion into the seminal vesicle and/or ejaculatory duct.
The spherical penis bulb is strongly muscularized, and longitudinally running muscle fibres also traverse the parenchyma of the penis papilla. The latter is, in its non-everted condition, a blunt cone with a vertical orientation.
Female Reproductive System
The ovaries are situated at the base of the anterior gut trunk, medially to the anterior pair of testicular follicles. Vitellaria are extensive and well-developed, and distributed throughout the body length.
The oviducts arise from the postero-lateral surface of the ovaries and run just laterally to the ventral nerve cords; they open separately into a dorsal branch of the bursal canal. This dorsal branch communicates with the dorsal portion of the male atrium.
From the antero-dorsal surface of the irregularly shaped copulatory bursa arises a narrow and dorsally running bursal canal. Soon, however, the canal bifurcates. One branch is at first very broad, whereas its distal portion shows a characteristic widening. Ventrally to the widening this branch of the bursal canal narrows considerably and, subsequently, opens into the atrium. The other branch of the bursal canal is much narrower and empties into the dorsal portion of the male atrium, meanwhile receiving the separate openings of the oviducts. The entire bursal canal is surrounded by a very thick layer of muscles, and is lined with cuboidal and nucleate cells.
The copulatory bursa is connected with a pair of the median intestinal diverticula.
Although no details on eye structure were mentioned by Kato (1931), his Fig.1 suggests that the eyes have distinct lenses.
Miroplana trifasciata has been collected from a freshwater habitat with waterplants like Ceratophyllum and Potamogeton (Kato 1931, 1955).
Type locality: Tokyo, on the border of the river Arakawa, 20 miles inland from its estuary. The species is known only from its type locality.
Since no specimens were available, the present account relies on the original species description.
No longer available.