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Sluys, 1989a

Overview
Diagnosis: Uteriporus pacificus Sluys, 1989a may readily be distinguished from its congener U. vulgaris by two features, viz. testicular follicles which occupy the entire space between ventral and dorsal body surface, and the absence of a bursa through which the receptacular ducts communicate with the exterior; in U. pacificus the receptacular ducts unite to a common duct which opens ventrally to the exterior, whereas in U. vulgaris the receptacular ducts open into a bursa-like organ that opens to the exterior.
Habitus: Fully stretched live specimens are 4.5-7 mm long and have a maximum width of 1-1.5 mm. Head truncate with small auricular protuberances; anterior body margin somewhat convex. Body margins running parallel towards rounded posterior end; slight constriction present at the level of the eyes. Dorsal surface light-brown, or reddish brown, with white body margin; ventral surface unpigmented. The eyes are set in pigment-free spots.

Alimentary System
The relatively large pharynx measures between one-fifth and one-fourth of the body length. The inner circular muscle layer of the pharynx is highly developed and is much thicker than the outer circular muscle layer. The mouth opening lies somewhat anterior to the posterior wall of the pharyngeal cavity.
The anterior ramus of the intestine gives off 3-4 pairs of lateral diverticula and extends, unbranched, anterior to the eyes. Each posterior intestinal ramus gives rise to about 8 lateral diverticula; the posterior rami do not meet in the hind end of the body.

Male Reproductive System
There are about 15 testicular follicles on either side of the body, occupying the entire space between dorsal and ventral body surface and extending from the level of the ovaries into the posterior end of the animal.
The vasa deferentia enlarge to form false seminal vesicles and enter separately the well-muscularized penis bulb. Within the bulb the ducts run side by side for some distance and, subsequently, unite to form the ejaculatory duct. The latter is lined with nucleate cells and is surrounded by a layer of circular muscles, while it opens at the tip of the penis papilla.
The penis consists of a strongly muscular, hemi-global bulb and a short, conical papilla. The parenchyma of the penis papilla is traversed by numerous, mainly circularly running muscle fibres. The papilla is lined with tall, nucleate cells and is provided with a wel-developed, subepithelial layer of circular muscles, which is overlain with a thin layer of longitudinal muscles.

Female Reproductive System
The vitellaria were not fully developed in the specimens examined; the follicles extend throughout the boody.
The ovaries are situated directly behind the brain, dorsally to the ventral nerve cords. The oviducts arise from the antero-lateral wall of the ovaries and open separately into the posterior end of the female genital duct. The latter is lined with cuboidal, nucleate cells and receives the openings of shell glands. Just before opening into the female genital duct the oviducts communicate with very small ducts which lead to the expanded, posterior portions of the receptacular ducts.
These receptacular ducts run on either side of the male copulatory apparatus, just in front of which the ducts unite to a short, vertically oriented, common section which ventrally opens to the exterior. The receptacular ducts are lined with cuboidal, nucleate cells, excepting their expanded posterior portions. The posterior end of the oviducts gives rise to a rounded or sac-shaped expansion which is filled with a more or less vacuolated, granular tissue, which is interspersed with nuclei.

Eyes
Each pigment cup contains three retinal cells and a well-developed lens.

Ecology
Uteriporus pacificus was collected from two localities on the coast of British Columbia, viz. Newcombe Harbour in the Petrel Channel, and Goose Bay (see above). In both cases the specimens were collected from under stones high in the tidal zone and in the vicinity of freshwater streams running to the sea.

Distribution
Type locality: Newcombe Harbour (54°43'N 130°05'W), Pitt Island, Petrel Channel, British Columbia.Uteriporus pacificus was collected from two localities on the coast of British Columbia, viz. Newcombe Harbour in the Petrel Channel (see above), and Goose Bay (51 23'N 127 40'W).

Material Examined, Type Material
Private collection I. R. Ball: Holotype, BC 24-12, Pitt Island, British Columbia, 12.08.1986, sagittal sections on 3 slides. Paratypes, BC 24-1, Pitt Island, 12.08.1986, sagittal sections on 2 slides; BC 24-2, horizontal sections on 1 slide; BC 24-3, sagittal sections on 2 slides; BC 24-4, sagittal sections on 2 slides; BC 24-5, sagittal sections on 2 slides; BC 24-6, sagittal sections on 2 slides; BC 24-7, horizontal sections on 1 slide; BC 24-8, horizontal sections on 2 slides; BC 24-9, transverse sections on 3 slides; BC 24-10, sagittal sections on 3 slides; BC 24-11, sagittal sections on 4 slides; BC 24-13, sagittal sections on 3 slides.
Private collection I. R. Ball: BC 7-1, Goose Bay (51°23'N 127°40'W), British Columbia, 31.07.1986, sagittal sections on 3 slides; BC 7-2, sagittal sections on 2 slides; BC 7-3, sagittal sections on 3 slides; BC 7-4, sagittal sections on 4 slides; BC 7-5, horizontal sections on 2 slides; BC 7-6, transverse sections on 3 slides.

Uteriporus pacificus