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Sluys, 1989a

Overview
Diagnosis: Pentacoelum hispaniensis Sluys, 1989a differs from its congeners mainly in the presence of (1) three retinal cells in each eye cup, (2) a copulatory bursa (a bursa is absent in P. fucoideum), and (3) dorsal testes throughout the body length.
Habitus: Preserved specimens are about 2.25 mm long and 0.87 mm wide. The anterior end is broadly rounded and the posterior end is rounded or truncated. The dorsal body surface shows a dense brown pigmentation, except for the body margins, a mid-dorsal stripe, and a band directly anterior to the eyes, which are pale. The ventral surface is pale.

Alimentary System
The pharynx is between one-seventh and one-sixth of the body length. The inner circular muscle layer of the pharynx is much thicker than the outer zone of circular muscles. The mouth opening lies at the posterior end of the pharyngeal pocket.
The anterior ramus of the intestine extends anterior to the eyes and gives off three pairs of postocellar diverticula.

Male Reproductive System
There are at maximum 15-20 testes on either side of the body. The small, dorsally situated follicles extend from anterior to the ovaries into the posterior end of the body. The vasa deferentia unite just outside the penis bulb to form a common vas deferens, which traverses the muscle layers of the bulb. Inside the bulb the common vas deferens expands to a seminal vesicle, which communicates with the ejaculatory duct. Common vas deferens and ejaculatory duct are lined with a nucleated epithelium and are surrounded by a well developed layer of circular muscles.
The penis papilla is covered with a high, nucleated epithelium which is underlain with a thick, subepithelial layer of circular muscles and a layer of longitudinal muscles.

Female Reproductive System
The 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 vitellarian follicles extend from anterior to the ovaries into the posterior end of the body, the follicles occupying the entire space between dorsal and ventral body surface.
The oviducts arise from the ventro-lateral wall of the ovaries and give rise to an extension which reaches anterior to the gonads. This anterior oviducal extension is between 0.05 and 0.1 mm long.
The posterior branches of the oviducts run laterally to the ventral nerve cords. At the level of the gonopore the oviducts communicate with the lateral bursae and, subsequently, turn towards the middle of the body and open separately into the bursal canal.
The oviducts come very close to the lateral bursae, so that the connecting branch between bursa and oviduct is very short. The lateral bursae consist of a rounded vesicle, lined with tall, vacuolated cells, which opens ventrally to the exterior through a stalk; the openings are on either side of the gonopore. The vesicle is surrounded by a distinct layer of interwoven muscle fibres, and the stalk receives the openings of erythrophilic glands.
The female copulatory apparatus consists of a copulatory bursa which communicates with the atrium through a bursal canal that runs parallel to the body surface. The copulatory bursa, which may be poorly delimited from the surrounding tissue, is lined with tall, vacuolated cells. The bursal canal is lined with cuboidal, nucleate cells which are provided with distinct cilia; the canal is surrounded by a layer of circular muscles. The expanded, distal section of the bursal canal receives the openings of shell glands.

Eyes
Each pigment cup contains three retinal cells, while a lens is absent.

Ecology
The specimens were collected from artificial irregation channels transporting freshwater from the river Xúquer to orange grooves near Algemesi, a village 30-40 km south of Valencia. These orange grooves are situated at about 20 km form the sea.

Distribution
Type locality: Algemesi, Spain.

Material Examined, Type Material
Z.M.A.: Holotype: V.Pl. 828.1, Algemesi, Spain, 18.09.1987, sagittal sections on 2 slides. Paratypes: V.Pl. 828.2, sagittal sections on 3 slides; V.Pl. 828.3, sagittal sections on 2 slides; V.Pl. 828.4, sagittal sections on 1 slide; V.Pl. 828.5, sagittal sections on 1 slide.

Pentacoelum hispaniensis