Diagnosis: Uteriporus vulgaris Bergendal, 1890 shows a superficial resemblance to Foviella affinis but may be distinguished from the latter by its more slender appearance, more rounded head, and the presence of two genital pores. With respect to anatomical features, Uteriporus may be recognized immediately by its regularly arranged testes and vitellaria, by the bursa in front of the male copulatory apparatus, and by the receptacular ducts.
Habitus: The length of living animals varies from 3.5 mm up to 9 mm and their width from 1 mm up to 1.75 mm. The head is rounded or slightly triangular. At the level of the eyes the body shows a slight constriction and thereafter it broadens gradually, reaching its maximum breadth at about 2/3 of the body length, measured from the front end. The hind end is obtusely pointed.
The colour of the dorsal surface is variable: milky-white, yellow-brown to pale brown. In the more heavily pigmented specimens the areas overlying the pharynx and copulatory organs are pale, while frequently the testes and intestinal branches show through the body wall. The ventral surface is unpigmented. The two eyes are set in small unpigmented areas at some distance from the anterior margin.
The pharynx is about one-fifth of the body length; the inner circular muscle layer is much thicker than the outer one. The three rami of the intestine give off, at regular intervals, furcated diverticula and, more rarely, unforked branches. Secondary diverticula are usually not present. The pre-ocellar branch of the intestine is generally devoid of lateral diverticula.
Male Reproductive System
The testes show a segmentally, pseudometameric, arrangement and are situated between the intestinal diverticula; there are one or two inter-intestinal follicles. The testes occur ventro-laterally and throughout the body length.
In the pharynx region the vasa deferentia form large false seminal vesicles, which narrow before separately penetrating the penis bulb. The ducts unite in the penis papilla to a seminal vesicle which empties into the ejaculatory duct.
The penis is conical and has a ventro-caudal orientation. The musculature of the bulb is well developed and consists of interwoven fibres. The male atrium is surrounded by a subepithelial layer of circular muscles, overlain by a layer of longitudinal fibres. Both these layers continue on the penis papilla, but the longitudinal one is very weak or absent at the tip of the penis. The ejaculatory duct and the part of the vasa deferentia within the penis, are surrounded by circular muscles.
Female Reproductive System
The small ovaries are situated directly behind the brain. The oviducts run dorso-laterally to the ventral nerve cords. Behind the male copulatory apparatus the oviducts curve medially and open separately into the female genital duct.
The vitellaria are well-developed, reaching from ventral to dorsal body surface and extending throughout the body length; the follicles lie medially to the testes.
A bursa is situated in front of the male copulatory apparatus and opens ventrally to the exterior through a separate pore. Receptacular ducts open laterally into the bursa. These receptacular ducts arise from the walls of the bursa-one duct on either side-and, subsequently, run backwards, laterally to the male copulatory apparatus. Posterior to the latter, the receptacular ducts communicate with the oviducts through a small duct. This small duct meets the oviducts just before the latter communicate with the female genital duct. The posterior section of the receptacular ducts may be expanded to greater or lesser extent. In contrast the the bursa, this swollen part or accessory seminal vesicle shows no real lumen but contains a more or less vacuolated, granular tissue in which sperm may be present. The recptacular ducts, which may contain sperm, are lined with cuboidal, nucleate cells and are surrounded by strong and regularly spaced circular muscle fibres.
The female genital duct empties via a small opening through the rear wall of the atrium and receives the openings of shell glands.
The musculature of the bursa consists of interwoven fibres. The female genital duct is surrounded by a layer of circular muscles.
The pigment cups house three retinal cells and have in front of their opening a rounded lens.
Karyology: The diploid complement consists of 16 metacentric chromosomes which decrease gradually in size (Ball 1976).
Life Cycle: The species may be found throughout the year. In The Netherlands, Den Hartog (1963) observed copulation and cocoons only in April. In Scandinavia reproduction takes place somewhat later in the year, viz. in May and June (Bergendal 1896). The cocoons are spherical, 1/2 mm in diameter, and unstalked (Den Hartog 1963).
U. vulgaris may be found in the eulittoral zone, sometimes slightly higher, under stones and other objects. The species may be common also in salt marshes under all kinds of objects, among algae or between the roots of plants. U. vulgaris is most abundant in a marine habitat but sometimes may be found in waters with a lower salinity. The species is resistant to salinity fluctuations (Den Hartog 1963).
Type locality: District Bohus (Bohuslän) (58oN 12oE) and Kullen peninsula (56°18'N 12°28'E), i.e western coast of Sweden. On the western coasts of the Atlantic, U. vulgaris has been recorded from the Island of Newfoundland, Quebec, New Brunswick, and Maine (cf. Tomkiewicz and Ball 1973). On the eastern side of the Atlantic Ocean the species occurs from the White Sea to the western coast of Sweden, in the Baltic as far as Kiel Bay, on the Dutch, Belgium and French coasts up to Ambleteuse, and in Great Britain and Ireland (Wilhelmi 1909, Southern 1912, Ax 1960, Den Hartog 1963, Stéphan-Du Bois and Masson 1965, Van der Velde 1976).
Private collection I. R. Ball: C4, St. Anne des Monts, Quebec, 24.06.1971, transverse sections on 3 slides; C3, sagittal sections on 2 slides; C5, Cap Renard, Gaspe' Peninsula, 25.06.1971, transverse sections on 2 slides; C470, Leighton Neck, Maine, 28.08.1973, sagittal sections on 2 slides.
B.M.N.H.: Type series Planaria amara: Holotype, 1922.214.171.124, whole mount; paratype: 19126.96.36.199-26, transverse sections on 7 slides.
No type specimen available.