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(Lehmensick, 1937)

Overview
Diagnosis: Ostenocula harmsi (Lehmensick, 1937) is characterized by (1) oviducts which open separately into the bursal canal, (2) a seminal vesicle in the penis bulb receiving the openings of the vasa deferentia, (3) shell glands which open into the bursal canal entally to the openings of the oviducts, (4) a pharynx of which the inner longitudinal muscle layer exceeds the diameter of the inner circular muscle layer.
Habitus: Preserved specimens vary from 0.62 x 0.49 mm to 1.55 x 0.65 mm. Hind and front end are rounded, the latter being devoid of tentacles. Two dark, pigmented patches occur along the anterior body margin. Pigmented patches further occur in front of, between and behind the eyes, extending backwards from the eyes in the form of two irregularly shaped bands. The eyes are set closely together and lie in an unpigmented area.

Alimentary System
The pharynx is about one-fourth of the body length. The inner longitudinal muscle layer of the pharynx is thicker than the inner circular muscle layer, which is unusual in marine triclads (Unfortunately, Lehmensick's statement on the relative thickness of these muscle layers is not in agreement with what has been depicted in his Fig.4: it shows a pharynx in which the inner circular muscle layer is considerably stronger than the inner longitudinal muscle layer. Since this figure, among others, has not been drawn by Lehmensick himself but by "F.X.W.", it is probably best to rely in this case on his description and not on the figure).
The anterior ramus of the intestine extends anterior to the eyes and gives off two pairs of pre-ocellar diverticula. Behind the eyes the anterior gut trunk gives rise to about 5 pairs of branched, lateral diverticula. The branches of the first pair of these diverticula, i.e. those directly behind the eyes, curve anteriad and extend anterior to the eye cups. These branches give rise to a number of secondary diverticula. From each posterior ramus arise about 7 branched, lateral diverticula. Behind the copulatory apparatus the two posterior rami unite into a short single branch, which gives rise to 2-3 pairs of lateral diverticula. The mouth opening is situated at the hind end of the pharyngeal pocket.

Male Reproductive System
The number of testes on either side of the body ranges from 30 to 35. They extend from the level of the ovaries up to the copulatory apparatus. The follicles are situated ventrally and with 3-4 together between the intestinal diverticula.
At the root of the pharynx, the vasa deferentia enlarge to form large false seminal vesicles. Behind the pharyngeal pocket the vasa deferentia curve dorso-medially, meanwhile diminishing in diameter, and open into a well-developed, oval-shaped seminal vesicle which lies at the base of the penis bulb. The vesicle is lined with a high, cuboidal epithelium. From the ventral surface of this seminal vesicle arises a broad ejaculatory duct which opens at the very blunt tip of the penis papilla. The ejaculatory duct is penetrated by the openings of highly developed penis glands, which lie in the penis but also in the parenchyma dorsally to the penis bulb. The ejaculatory duct is lined with a low epithelium. The musculature of the penis bulb is well developed. The penis papilla is a broad, barrel-shaped structure; its lining epithelium is underlain with a well developed subepithelial layer of circular muscles and a thinner layer of longitudinal muscles. Both muscle layers are continuous with the equally well developed muscle layers around the male atrium. The male atrium communicates with the gonopore via a considerable constriction.

Female Reproductive System
The vitellaria extend from the level of the ovaries into the hind end of the body.
The paired ovaries are situated directly behind the brain. The oviducts run laterally to the ventral nerve cords. Behind the gonopore the oviducts curve medially and open separately into the bursal canal. Shortly before communicating with the canal, the oviducts receive the secretion of shell glands.
The bursal canal arises from the anterior surface of the globular copulatory bursa. The proximal section of the canal runs at first obliquely towards the dorsal body surface, but then makes a sharp, ventrally directed bend, so that the distal portion of the bursal canal runs obliquely towards the ventral body surface. Just ectally to the openings of the oviducts, the bursal canal shows a constriction, but the main effect on the lumen of the canal in that region is caused by an annular outbulging of the lining epithelium. Entally to the openings of the oviducts the lumen of the bursal canal expands again. The canal is surrounded by a well developed subepithelial layer of circular muscles and a thinner layer of longitudinal muscle fibres.
The majority of the shell glands open into the section of the bursal canal entally to the openings of the oviducts. The glands are distributed around the bursal canal.

Eyes
The pigment cups house three retinal cells and a large, globular lens.

Ecology
Specimens of O. harmsi were found in a seawater aquarium of a marine biological institute in Jakarta (Batavia). The seawater had been obtained from a seawater basin in Jakarta.

Distribution
Type locality: Jakarta, Java. Specimens of O. harmsi were found in a seawater aquarium of a marine biological institute in Jakarta (Batavia). The seawater had been obtained from a seawater basin in Jakarta. This forms the only locality from which the species has been reported.

Material Examined and Type Material
The type material is no longer available. Because no new material has become available, the present account is based on Lehmensick's description

Ostenocula harmsi