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Sluys and Ball, 1989

Overview
Diagnosis: Obrimoposthia acuminata Sluys and Ball, 1989 can be distinguished easily from the other members of its genus by its large, pointed penis papilla, by the presence of large glands discharging dorsally to the exterior, as well as by the different construction of the bursal canal and its surrounding muscle layers.
Habitus: Preserved specimens measure up to about 3.75 mm in length and 2.5 mm in breadth. Front and hind end are rounded; there are no tentacles. The dorsal surface is greyish black and provided with numerous small, brown-black, pigment granules. An unpigmented, rather large spot occurs along the antero-lateral margin on either side of the body. The ventral body surface is grey-green and also provided with small pigment granules, though much less in number than on the dorsal surface. The eyes are situated just behind the posterior margins of the unpigmented spots.

Alimentary System
The pharynx lies in the middle of the body and is between one-fourth and one-third of the body length. The inner circular muscle layer of the pharynx is much thicker than the outer circular muscle zone. The mouth is situated in the posterior portion of the pharyngeal pocket, somewhat anterior to the hind wall of the pharyngeal pouch.
The anterior ramus of the intestine extends anterior to the eyes without giving off pre-ocellar diverticula. Behind the eyes the anterior ramus gives off three pairs of branched, lateral diverticula. Each of the posterior intestinal rami gives rise to about 12 lateral diverticula. The tips of the posterior branches unite behind the copulatory apparatus.

Male Reproductive System
There are about 30-40 ventrally situated testes on either side of the body, extending from directly behind the ovaries up to the hind end of the copulatory bursa.
At about the level of the posterior third of the pharyngeal pocket, the vasa deferentia enlarge to form false seminal vesicles. At the hind end of the pharyngeal pocket the ducts curve dorso-medially and narrow gradually while ascending towards the penis bulb. The vasa deferentia narrow considerably when entering the penis bulb. Inside the bulb each vas deferens enlarges to a small, elongated accessory seminal vesicle, which, subsequently, gradually tapers during its course in the penis papilla. In the proximal portion of the penis papilla the vasa deferentia come very close together and, subsequently, unite to a short common vas deferens. This common vas deferens opens into the funnel-shaped proximal portion of the ejaculatory duct, which also receives the secretion of penis glands. The wall of the ejaculatory duct consists of a low infranucleate epithelium. The accessory seminal vesicle, vasa deferentia, and common vas deferens are surrounded by irregularly arranged, more or less circularly running muscle fibres. The same type of musculature surrounds the ejaculatory duct.
The penis consists of a shallow bulb and a large conical papilla. The musculature of the bulb is well developed and consists of interwoven fibres. The proximal portion of the papilla has an oblique, ventro-caudal, orientation and is provided with an extremely thick layer of strong circular muscle fibres. The pointed distal portion of the penis papilla is bent towards the ventral body surface, the tip piercing through the gonopore or being folded inside the atrium. The highly developed circular muscle layer extends, albeit much thinner, on the distal part of the penis papilla. Entally to this circular muscle layer there is a well developed, but much thinner layer of longitudinal muscles which is continuous with muscle layers on the bulb as well as with longitudinal layers around the atrium. The proximal portion of the penis papilla is traversed by longitudinal muscles which extend outside of the penis bulb; these muscle fibres converge towards the funnel-shaped portion of the ejaculatory duct.
The male atrium is narrow, its proximal portion being lined with a tall, nucleate epithelium. The nuclei are situated at the bases of the cells, which are filled with bright red staining granules. The distal portion of the atrium is lined with a much lower epithelium of which the cells are devoid of the granular secretion. The tall epithelial cells of the atrium are underlain with a thick circular muscle layer, overlain with a longitudinal muscle layer. On the distal portion of the atrium both muscle layers become much thinner.

Female Reproductive System
The small, rounded ovaries are situated at some distance behind the brain, in some cases at almost half-way the distance between the brain and the root of the pharynx; they lie medially to the ventral nerve cords. The oviducts arise from the dorso-lateral surface of the ovaries. In following their course backwards, the oviducts find their way just dorsally to the testes or between the dorsal tips of the testicular follicles. Behind the gonopore the oviducts turn medially and unite to a common oviduct which opens into the proximal portion of the bursal canal.
The part of the bursal canal situated between the bursa and the opening of the common oviduct is lined with a tall, infranucleate epithelium. The remaining part of the bursal canal is lined with a much lower, but still infranucleate, epithelium. The section of the bursal canal immediately ectally to the opening of the common oviduct is rather narrow but the canal enlarges and, subsequently, narrows again before communicating with the atrium. The entire distal part of the bursal canal is provided with cilia, and shell glands open into the broadened portion of the canal. These shell glands are situated ventrally to the copulatory bursa as well as behind and ventrally to the male atrium. The bursal canal is surrounded by a well developed layer of circular muscles, overlain with a much thinner layer of longitudinally running muscle fibres. Oviducts and common oviduct are surrounded by thin layers of circular muscle fibres.
The vitellaria are well developed. They are situated dorsally to the testicular follicles and extend from directly anterior to the ovaries into the hind end of the body.

Eyes
The pigment cups contain two retinal cells and a large oval-shaped lens.

Glands
Obrimoposthia acuminata possesses large glands which lie beneath the dorsal body surface and which discharge dorsally to the exterior (cf. Sluys and Ball 1989: Fig.8; Plate 00). Each gland consists of a more or less globular body with a mushroom-shaped projection that pierces the dorsal epidermis and which carries on its cap a number of finger-like projections. Tiny droplets are attached to these projections. The ventral surface of the globular body shows densely bright red staining material which, to greater or lesser extent, also may be present in what appears to be the lumen of the rounded body. The rest of the body as well as the mushroom-shaped part, consists of dense, granular flesh-coloured material. The entire globular body is surrounded by the pigment granules which lie in the parenchyma. The globular body measures about 33.75 um in diameter and 43.75 um in height. The diameter of the cap of the mushroom is about 17.5 um, whereas the projections on top of it are about 7.5 um in height. The glands appeared to be distributed irregularly underneath the entire dorsal surface and not to be confined to particular areas. Surprisingly, only in part of the specimens examined these large glands were present. In most of the sagittally and transversally sectioned specimens glands could not be discerned. Type specimen W5523-2 showed many well developed glands, and these also occurred, albeit in smaller numbers, in specimen W5523-6. Very few glands were found in specimen W5523-5.

Reproduction
Life Cycle: Two specimens in sample W5524 had a cocoon in their atrium. The cocoons were rounded with a diameter of about 0.85 mm and had a pedicel which was attached to an endplate of about 0.1 mm in diameter.

Ecology
The animals live in a non-marine biotope since they were collected from amongst boulders in a freshwater stream which flowed onto the beach (P. Hutchings).

Distribution
Type locality: Enderbey Island, Auckland Island, New Zealand. The species is known only from the type locality.

Material Examined and Type Material
A.M.: Holotype: W5523-2, Enderbey Island, Auckland Island, New Zealand, 22.02.1973, sagittal sections on 5 slides.
Paratypes: W5523-1, horizontal sections on 3 slides; W5523-3, sagittal sections on 4 slides; W5523-4, horizontal sections on 2 slides; W5523-5, transverse sections on 5 slides; W5523-6, sagittal sections on 4 slides; W5523-7, sagittal sections on 5 slides; W5524-1, sagittal sections on 3 slides; W5524-2, sagittal sections on 3 slides; W5524-3, horizontal sections on 2 slides; W5524-4, transverse sections on 4 slides; W5524-5, horizontal sections on 2 slides; W5524-6, sagittal sections on 3 slides; W5524-7, transverse sections on 4 slides; W5524-8, sagittal sections on 3 slides. Preserved specimens from the two samples from which the type specimens were obtained.

Obrimoposthia acuminata