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Sluys and Ball, 1989

Overview
Diagnosis: Puiteca rigida Sluys and Ball, 1989. Because of its peculiar external appearance, P. rigida may at first sight be distinguished from any other triclad known to date. The characteristic large, chitinized penis papilla is already visible in preserved specimens and unlike that of any other triclad.
Habitus: The preserved specimens were about 1.5 mm long and the largest breadth, just in front of the pharynx, was about 0.87 mm.
The anterior half of the body is of a broad triangular shape, with the eyes situated in the middle of that part. A few shallow indentations divide this anterior part into a number of lobes, which are arranged symmetrically on both sides of the body. In the holotype the anterior margin of the body, i.e. the apex of the triangular part, was undivided. In the paratype this portion was divided into two lobes by a shallow indentation. Immediately posterior to the apex a small rounded lobe is situated on either side of the body. The remaining part of the triangular-shaped frontal part consists of two broad lobes, of which the mid-portions show a shallow outbulging. The posterior half of the body consists of a short "waist" and four large, muscularized suckers at the hind end of the body. On either side of the body, somewhat before the posterior end, there is a dorsal, cup-shaped sucker. The two broad ventral suckers are not cup-shaped but consist of bean-shaped structures with a flat ventral surface which are connected at the posterior margin of the body. The animals are unpigmented.

Alimentary System
The pharynx is oriented at right angles to the body axis, i.e. it hangs down from the roof of the pharyngeal pocket. The inner circular muscle layer of the pharynx is much thicker than the outer zone of circular muscles. The mouth opening is situated at the front end of the pharyngeal pocket.
The anterior ramus of the intestine consists of a short, undivided branch which extends anterior to the pharyngeal pocket and stays well behind the brain. Each posterior ramus gives off about four, unbranched lateral diverticula. Although I was unable to establish the precise course of the posterior intestinal rami in the preserved specimens, I got the impression from the sections that no communications existed between both branches, which extend into the hind end of the body.

Male Reproductive System
There are about 4-5 large testes on either side of the body. The testicular follicles extend from somewhat anterior to the level of the penis bulb, i.e. in front of the ovaries, to about the level of the gonopore. The testes are situated dorsally, although some of the follicles are elongated and almost extend to the ventral body surface.
The testes discharge into a single vas deferens which enlarges to form a winding false seminal vesicle. Before entering the penis bulb, the false seminal vesicle tapers to a narrow duct. Inside the bulb this duct opens into a seminal vesicle which, via a glandularized sort of diaphragm, opens into another seminal vesicle. This latter vesicle communicates via a constriction with the ejaculatory duct, of which the proximal portion is somewhat wider than the narrow part that runs through the penis papilla.
Two types of secretion are discharged into the proximal portion of the ejaculatory duct. The first type is a brown-yellow, granular secretion which probably comes from gland cells situated outside the penis bulb. The second type of secretion is not granular and appears in the form of densely red staining patches and stripes; it is most likely discharged by the unicellular glands which lie in the posterior part of the penis bulb. A similar type of secretion was present throughout the penis papilla, but most of the secretion was accumulated in the distal part of the papilla, giving the tissue a dominant red hue.
In the holotype it was impossible to discern the ejaculatory duct in the penis papilla. But in the paratype a narrow duct, surrounded by a thin circular muscle layer, appeared to be situated in the center of the penis papilla. However, neither the holotype, nor the paratype provided information on the opening of the ejaculatory duct to the exterior. The holotype suggested that the ejaculatory duct does not open at the tip of the papilla.
The penis bulb is surrounded by a well developed layer of longitudinal muscle fibres. The penis papilla is a long rod-like structure, of which the proximal half runs more or less parallel to the body surface, whereas the distal part bends towards the ventral surface. The papilla is lined with an amorphous, sclerotized cuticula. This cuticula probably results from sclerotization of the usual penis epithelium since it is in line with the epithelium lining the basal part of the papilla, which is continuous with the epithelium lining the male atrium. At the proximal portion of the penis papilla the cuticula follows a wavy course, but on the greater part of the papilla it is straight. In several places, mostly on the distal part of the papilla, the cuticula gives rise to spines. No muscles seemed to be present underneath the cuticula.
The elongate male atrium houses the penis papilla and is surrounded by a thin layer of circular muscle fibres, overlain with a thin layer of longitudinal fibres. The distal portion of the male atrium is rather narrow and communicates with the common atrium.

Female Reproductive System
The small ovaries are situated behind the pharyngeal pocket and lie medially to the ventral nerve cords. A distinct germ centre is located in the posterior inner part of the ovaries. The oviducts arise from the ventral surface of the ovaries. At first the ducts run laterally, but then make a caudally directed bend and follow their course just above the ventral nerve cords. The anterior part of the oviducts is narrow and has a diameter of about 7.5 um. However, the posterior section of the oviducts, i.e. near the point where they open separately into the bursa, consists of a thick-walled tube, which is surrounded by a rather thick circular muscle layer. This posterior part of the oviducts has a diameter of about 15 um.
The vitellaria may occupy the entire space between dorsal and ventral body surface and extend from the level of the anterior intestinal ramus up to the gonopore.
The oviducts open into a small sac-shaped vesicle, lined with a low, cuboidal and nucleate epithelium which lacks cilia. From the antero-ventral surface of this vesicle arises a short canal or female genital duct, which opens into the atrium. This canal is composed of a nucleate, non-ciliated epithelium and receives the openings of well developed shell glands. The vesicle is surrounded by a thin layer of circular muscle fibres.
A rather large, egg-shaped copulatory bursa is located just beneath the proximal part of the male atrium. This bursa is made of a low, nucleate epithelium which is devoid of cilia. A large, cone-shaped clump of sperm is attached to the dorsal wall of the bursa. A bursal canal arises from the posterior surface of the bursa. This canal runs at first ventrally, but then makes a strong caudally directed bend, so that its distal portion is at right angles with the proximal section; the distal part of the bursal canal opens into the atrium. The broad bursal canal is lined with a tall epithelium and its lumen increases gradually in diameter. The nucleate epithelium lining the wide distal part, which communicates with the atrium, is provided with long, anteriorly curved cilia. The tall epithelial cells of the dorso-ventrally running part of the bursal canal are devoid of cilia; all cells are probably nucleate, although this could be determined with certainty only for a part of the canal close to the bursa.
The difficulty of discerning nuclei in the cells is caused by the fact that the entire bursal canal receives the openings of glands, the secretion of which makes the cells stain densely red. The bursal canal is surrounded by a thick layer of circular muscle fibres. On the distal, broadened portion of the canal a very thin layer of longitudinal was present entally to the thick circular muscle layer. No muscles seemed to surround the copulatory bursa. Immediately interiorly to the muscle layer(s) of the bursal canal there are numerous densely red staining, unicellular, gland cells. These small glands discharge into the bursal canal, their secretion accumulating in the lining cells.

Eyes
The pigment cups contain three retinal cells. There is no lens to the eyes.

Ecology
The type specimens have been dredged from muddy sand at a depth of 60 m.

Distribution
Type locality: Bass Strait, Australia, at 40°13.8'S 148°39.6'E. The species is known only from the type locality.

Material Examined, Type Material
M.V.: Holotype: G3437-1, Bass Strait, Australia, 40°13.8'S 148°39.6 E, 14.11.1981, sagittal sections on 2 slides; Paratype: G3437-2, transverse sections on 2 slides.

Puiteca rigida