Sluys, 1989a
Overview
Diagnosis: Oregoniplana pantherina Sluys, 1989a may readily be distinguished from other triclads, excepting O. opisthopora, by the following combination of features: (1) presence of a caudal pore which via a duct communicates with the copulatory appartus, (2) two large testes, (3) ovaries that open into large sacs which in turn communicate with the oviducts, (4) presence of a ciliated sensory duct which meets the brain. O. pantherina differs from O. opisthopora in that in the latter the ovaries open into the dorsal portion of the stromatic sacs, whereas in the former communication occurs ventrally. Other differences between the two species concern the absence or presence of preocellar diverticula, and the pattern of pigmentation.
Habitus: The living animal was 5 mm long and 2 mm wide. "Colour very pale brown with red sepia spots on back and a few paler ones ventrally; a pair of eyes towards anterior end" (J. F. G. Wheeler, field notes).
Alimentary System
The small pharynx is situated in the posterior half of the body and is about one-tenth of the body length. The inner circular muscle layer of the pharynx is only slightly thicker than the outer circular muscle layer. The mouth opening is at the hind end of the pharyngeal pouch.
The anterior ramus of the intestine extends anterior to the eyes, without giving rise to preocellar diverticula.
Reproductive System
With respect to the copulatory appartus the following description relies solely on Bock's sketches. From these it is evident that there must have been another set(s) of sagittal sections with the copulatory appartus which, unfortunately, is not present among the available material.
A pair of large testes is situated just anterior to the pharynx; the follicles occupying the entire space between dorsal and ventral body surface.
At the level of the pharynx the vasa deferentia expand to form large false seminal vesicles. It is not known whether the vasa deferentia unite before entering the penis or only fuse within the penis papilla.
The penis is a large and pointed cone, with an unusual orientation. In following the course of the male atrium the proximal portion of the penis runs anteriad, whereas its distal half curves towards the ventral body surface, so that eventually the tip of the papilla points to the hind end of the body. The ejaculatory duct opens at the tip of the penis papilla and the base of the duct expands to form an accessory seminal vesicle.
The male atrium communicates with the exterior through the gonopore as well as through connection with a duct that leads to the caudal pore.
The vitellaria are well developed, extending from anterior to the ovaries into the hind end of the body; the follicles occupying the entire space between dorsal and ventral body surface.
The paired ovaries are situated at some distance behind the brain, viz. between one-fourth and one-third of the distance between the brain and the root of the pharynx. The structure of the ovaries is rather curious but reconstruction proved complex since only one set of transverse sections is available.
The ovaries have more or less the shape of a tadpole, the germ centre lying in the dorsally situated "head". The ventral portion of the ovaries tapers to form a sort of duct that curves laterally, thus representing the tail of the tadpole. This duct seems to communicate with a large, more or less sac-shaped structure (stromatic sac) that lies immediately laterally to the ovary and that partly envelopes the latter. This structure is made up of small, ill-defined and nucleate cells, while from its lateral wall the oviduct arises. No sperm was observed in these sac-shaped structures. The oviducts follow their course backwards laterally to the ventral nerve cords. Bock's sketches do not give information on the communication between oviducts and female copulatory apparatus.
What I consider to be the female copulatory apparatus only consists of a small atrium which receives the openings of shell glands. At its rear this female atrium communicates with a duct that leads to a caudal pore.
Sense Organs
The paired eyes are situated in front of the brain. The fine structure of the eyes is not very well preserved in the specimen, but I got the impression that each of the unicellular pigment cups contains many retinal cells and that a lens is absent.
In front of the eyes and on both sides of the body the dorsal epidermis gives rise to an invagination which leads into a long and well developed duct. This duct is lined with cuboidal, nucleate cells which bear well developed cilia. The duct runs posteriorly for a long distance and eventually meets the lateral surface of the brain.
Ecology
The species was collected from "Kelp roots".
Distribution
It is known only from the type locality, Jut Bay, near Saldanha Bay, South Africa.
Material Examined, Type Material
B.M.N.H.: 1988.2.23.2, one specimen sectioned as follows: one set of sagittal sections of the hind end of the body on 1 slide, and one set of transverse setions of the front end on 6 slides, coll. J. F. G. Wheeler, 23.09.1926.