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(Hyman, 1958)

Overview
Diagnosis: Allogenus kerguelenensis can be distinguished easily by its small, posteriorly located pharynx and by the fusion of the posterior rami of the intestine, resulting in a short single branch. With respect to anatomical features the species is characterized by an irregularly shaped copulatory bursa, which is connected with the rest of the female copulatory apparatus by a very narrow and short duct.
Habitus: Preserved specimens have a slender appearance and are about 7 mm long and 1.25 mm wide. The largest diameter occurs at the level of the posteriorly situated pharynx. From that point, the body margins taper towards the obtusely pointed hind end, and run parallel towards the rounded front end. Specimens are devoid of pigment and, as a consequence, pharynx, copulatory apparatus, intestine and vitellaria are clearly visible through the body wall. Living animals are whitish (Hyman 1958). The two very small eyes are at some distance from the anterior margin and are set close together; they are closer to each other than each of them is removed from the lateral body margin.

Alimentary System
The small pharynx-it is about one-seventh of the body length-is situated in the posterior part of the animal. The inner circular muscle layer of the pharynx is at least in the anterior half of the pharynx much thicker than the outer circular muscle layer. The mouth opening is situated at the hind end of the pharyngeal pocket.
The long anterior ramus of the intestine terminates between the eyes and gives off about 16 pairs of mostly forked, lateral diverticula. Before uniting behind the copulatory apparatus, each posterior intestinal trunk gives rise to about 10 lateral diverticula, which are mostly unbranched. Short, medially directed diverticula are also present. The posterior intestinal rami unite to a short common branch that extends into the hind end of the body; it gives off three pairs of unbranched lateral diverticula.

Male Reproductive System
The numerous testes are principally situated ventrally but their dorsal portion may extend to almost the dorsal body surface. The follicles extend from directly behind the ovaries to somewhat anterior to the root of the pharynx. There are about three follicles in each intestinal septum.
At the level of the hind part of the pharyngeal pocket, the vasa deferentia enlarge to form false seminal vesicles. Both ducts narrow gradually while ascending towards the penis bulb and unite just outside the latter to form a short and narrow common vas deferens. Shortly after having entered the penis bulb, the common vas deferens expands to form a large, rounded seminal vesicle which tapers distally into the non-ciliated ejaculatory duct. The latter opens acentrally at the tip of the penis papilla. The short common vas deferens, the seminal vesicle, and the ejaculatory duct are lined with cuboidal, nucleate cells. Penis glands could not be discerned in the specimens studied.
The penis is conical and may have an oblique, ventro-caudal, disposition or it may show a more or less horizontal orientation; the tip is blunt. The musculature of the penis bulb is only weakly developed. The seminal vesicle is surrounded by a well developed layer of muscles which, albeit much thinner, continues on the ejaculatory duct. The penis papilla is only provided with thin layers of circular and longitudinal muscle fibres but may also show fibres which traverse the papilla from its lining epithelium towards the ejaculatory duct.

Female Reproductive System
The two small, globular ovaries are situated behind the brain at about one-third of the distance between the former and the root of the pharynx; they lie medio-dorsally to the ventral nerve cords. The oviducts arise from the ventro-lateral surface of the ovaries and in running backwards the ducts stay laterally to the nerve cords. Behind the genital pore the oviducts turn medially and unite to a common oviduct. The nucleate common oviduct (or female genital duct ?) is ciliated and receives the secretion of shell glands; it is surrounded by a layer of circular muscles. The common oviduct communicates with the atrium.
The vitellaria are well developed and extend from anterior to the ovaries into the hind end of the body. The main body of the vitellaria is situated ventrally but the follicles may also extend dorsally to well beyond the mid-line of the animal and sometimes even extend to the dorsal body surface.
The copulatory bursa is an irregularly shaped vesicle which opens via a short and narrow duct into the common oviduct. This short duct is surrounded by a well developed layer of circular muscles. The bursa of the holotype is lined with tall, vacuolated cells bearing long cilia. In the specimen from Macquarie Island the copulatory bursa is completely filled with sperm and an unidentifiable, vacuolated mass. The bursa has no musculature of its own; what in first instance appears to be bursal musculature are in reality parenchymal muscle fibres traversing the body in dorso-ventral direction.

Eyes
Two retinal cells could be discerned in each pigment cup, which also houses a rounded lens.

Ecology
A. kerguelenensis has been collected from "under rocks between tide marks at Kerguelen" (Hyman 1958), and from the intertidal zone at Macquarie Island (Material Examined).

Distribution
Type locality: Kerguelen. A. kerguelenensis has been collected from "under rocks between tide marks at Kerguelen" (Hyman 1958), and from the intertidal zone at Macquarie Island (Material Examined).

Material Examined
S.A.M.: Holotype: V3126, Kerguelen, 13.11.1929, sagittal sections on 2 slides; paratype: V3125, whole mount, taken from the same vial as the holotype.
Z.M.A.: V.Pl. 825, Macquarie Island, 24.02.1965, sagittal sections on 1 slide.

Type Material
S.A.M.: Holotype: V3126, Kerguelen, 13.11.1929, sagittal sections on 2 slides; paratype: V3125, whole mount, taken from the same vial as the holotype.

Allogenus kerguelenensis