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(Westblad, 1952)

Diagnosis: Synsiphonium anderssoni (Westblad, 1952), as compared with other bdellourids, is characterized by two large testes, and the spermiduct branches which open directly to the exterior and do not communicate with lateral bursae, which are absent in this species.
Habitus: Preserved specimens up to 1.5 mm long and 0.37-0.9 mm wide. The dorsal surface may either be white or be provided with pigment, in the latter case the pigmentation being concentrated around the testes, the copulatory apparatus and in the form of a brownish patch anteriorly to the eyes. The ventral surface is pale.
The body shape of preserved specimens varies from elongate to broadly oval-shaped, in both cases with rounded front and hind end.

Alimentary System
The pharynx lies in the posterior half of the body and measures up to about one-seventh of the body length. Both inner and outer circular muscle layer of the pharynx are well developed and of equal thickness. The mouth opening lies at the hind end of the pharyngeal cavity.
The anterior ramus of the intestine extends as an undivided branch anteriorly to the eyes. Between the ovaries and the testes the anterior gut trunk gives rise to a pair of branched lateral diverticula. Each of the caudally running gut trunks gives off about 5 lateral diverticula, whereas the rami do not meet in the hind end of the body.

Male Reproductive System
A pair of big testes is situated between the ovaries and the root of the pharynx, the follicles occupying the entire space between dorsal and ventral body surface. The vasa deferentia arise from the median wall of the testes and expand to form large false seminal vesicles. The vasa deferentia unite just outside the penis bulb to a short common vas deferens, which penetrates the weakly developed bulb. Within the penis the common vas deferens communicates with the ejaculatory duct, which is penetrated by the openings of penis glands. In specimens with a short, contracted penis an intrapenial papilla is present, through which the common vas deferens opens into the ejaculatory duct. This intrapenial papilla may be developed to greater or lesser extent. The common vas deferens is lined with a nucleate epithelium, and the ejaculatory duct is provided with the same, albeit less distinct epithelium.
The penis papilla has the form of an elongated cone, filling entirely the elongate male atrium. However, the papilla may be contracted to a considerable degree, in which case it has the shape of a plump cone. The papilla is provided with a thick, subepithelial layer of circular muscles which is entally bounded by a thinner layer of longitudinal muscles.

Female Reproductive System
The vitellaria are well developed and extend from anteriorly to the ovaries into the hind end of the body, occupying the entire space between dorsal and ventral body surface.
The ovaries are situated between the testes and the brain, usually directly behind the latter; they lie dorsally to the ventral nerve cords. The oviducts arise from the ventro-lateral wall of the ovaries and run laterally to the ventral nerve cords. Behind the gonopore the oviducts open separately into the female genital duct. The last-mentioned duct is lined with nucleate, ciliated cells and receives the secretion of shell glands ectally to the openings of the oviducts. The female genital duct communicates with the atrium and with a branch of the intestine.
From the ventro-lateral wall of the ovaries also arise spermiducts which unite at a short distance behind the gonads to form a sometimes considerably expanded, common section. This common part bifurcates at the root of the pharynx, each of the branches running backwards to the level of the gonopore. Here, each spermiduct branch opens ventrally to the exterior, just laterally to the gonopore. The spermiducts are lined with tall or cuboidal, nucleate cells and are surrounded by a weakly developed layer of circular muscles. Sperm may be present in the lumen of the spermiducts and also in vacuoles of the cells lining the common section between the ovaries and the pharynx.

Each eye cup contains a rounded lens and an unknown number of retinal cells.

S. anderssoni has been found in tide pools and at depths ranging from about 8 m to 36 m, and has been collected from seaweed (Kelp), fine sand, rubble-stones, gravel, and shells.

Type locality: As type locality has been designated the sampling locality from which the major part of the type material was obtained, viz. South Georgia. The species is known from South Georgia (Westblad 1952, Material Examined); Tierra del Fuego (at 54°43'S 64°08'W), and eastern mouth of the Beagle Channel at 54°32'S 68°25'W, i.e. S.S.P stations 3 and 64, respectively (Westblad 1952, Material Examined); two localities in New Zealand, viz. Taiaroa Head, Dunedin and Goat Island at 36°16'S 174°47'37"E (Material Examined); Arthur Harbour (64°46'36"S 64°03'29"W); Port Lockroy (Goudier Islet, Graham Land, 64°50'S 63°30'W).

Material Examined and Type Material
C.M.: IZ 3521/1, Taiaroa Head, Dunedin, New Zealand, 5.03.1983, sagittal sections on 1 slide; IZ 3521/2, sagittal sections on 1 slide; IZ 3521/3, Goat Island, New Zealand, 7.12.1982, sagittal sections on 1 slide.
B.M.N.H.: 1988.2.23.11, Port Lockroy, Goudier Islet, 30.10.1944, sagittal sections on 1 slide; 1969.11.25.2-5, Arthur Harbour, Antarctica, 25 Jan. 1969, whole mount on 1 slide.
S.M.N.H.: Type series: South Georgia, Grytviken, 23.5.1902, sagittal sections on 1 slide, 2 whole mounts on 1 slide; 22.5.1902, sagittal sections on 2 slides, transverse sections on 1 slide, transverse sections on 2 slides, and horizontal sections on 1 slide; 25.5.1902, transverse sections of front end and sagittal sections of hind end, each series mounted on a separate slide; Swedish South Polar Expedition, station 3, 6.1.1902, sagittal sections on 1 slide; station 64, 30.10.1902, sagittal sections on 1 slide; Grytviken, S.S.P. station 3, 6.1.1902, transverse sections on 2 slides.

Synsiphonium anderssoni