Hallez, 1911
Overview
Diagnosis: Synsiphonium liouvilli Hallez, 1911 can be distinguished from its congeners by the following combination of features: (1) ventral testes, (2) communication between oviducts, spermiducts, and ovaries taking place at the antero-dorsal surface of the latter, (3) one eye lens in each pigment cup, (4) very large and sinuously folded lateral bursae.
Habitus: Preserved specimens up to about 8 mm long and 7 mm wide. The size of living specimens may be up to 12 x 6 mm. In preserved animals the body may be elongate with broadly rounded front and hind end. In other cases, however, the body is very broad, the largest diameter being at about the hind end of the pharyngeal pouch; the hind end is broadly rounded or even somewhat truncated, whereas the body margins taper towards the much narrower front end.
The dorsal body surface is grey-brown or, according to Hallez (1913), zinc-grey; the ventral surface is paler. A pale spot is situated on either side of the antero-lateral margin. The field notes of J. F. G. Wheeler describe living specimens as having an opaque white colour with a very light brownish tint, and with a conspicuous pair of eyes.
Alimentary System
The short pharynx is situated in the posterior half of the body and measures between one-nineth and one-fourth of the body length. The outer layer of circular muscles of the pharynx may either be slightly thicker than the inner layer of circular muscles or it may be considerably thicker than the last-mentioned layer. The mouth opening is at the hind end of the pharyngeal cavity.
The anterior ramus of the intestine extends anterior to the eyes, giving off 2-3 pairs of preocellar diverticula. Behind the eyes the anterior gut trunk gives rise to 8-15 lateral diverticula. The posterior rami meet in the hind end of the body.
Male Reproductive System
The numerous testes are situated ventrally, and extend from directly behind the ovaries up to about the level of the male atrium. The total number of testicular follicles present is related to the size of the animals; it may vary from 40-50 (Westblad 1952, Material Examined) to 160 (Hallez 1913, Material Examined), and in the largest animals examined the number of follicles was as large as 300.
In the pharynx region the vasa deferentia enlarge to form false seminal vesicles which decrease considerably in diameter before penetrating the penis bulb. Communication between vasa deferentia and ejaculatory duct is variable. In some specimens the vasa deferentia penetrate the penis bulb and, subsequently, unite to form a common vas deferens which communicates with the ejaculatory duct. In other cases the vasa deferentia open separately into the proximal part of the ejaculatory duct.
In other specimens an intrapenial papilla may be developed to greater or lesser extent. The vasa deferentia may either unite within this intrapenial papilla to form a short common duct, or they may form a common vas deferens before entering the intrapenial papilla. The common vas deferens opens at the tip of the intrapenial papilla. Common vas deferens and the sections of the vasa deferentia within the penis bulb are surrounded by a well developed layer of circular muscles. In all of the situations described above the vasa deferentia penetrate separately the penis bulb, while the ejaculatory duct receives the numerous openings of penis glands; the duct is lined with a nucleate, ciliated epithelium.
The penis bulb is usually well developed and rather strongly muscularized. The penis papilla generally shows a horizontal orientation but its shape and size are highly variable. The size of the papilla may range from very small to very large, but it is always provided with a strong layer of subepithelial circular muscles, overlain with a much thinner layer of longitudinal muscles. The penis papilla projects into a usually rather spacious atrium which communicates with the gonopore and the bursal canal.
Female Reproductive System
The vitellaria extend from anteriorly to the ovaries into the hind end of the body and occupy the entire space between the dorsal and ventral body surfaces.
The ovaries are situated at a short distance behind the brain, medially to the ventral nerve cords. The oviducts arise from the antero-dorsal surface of the ovaries and, subsequently, they run backwards laterally to the ventral nerve cords. In the hind end of the body the oviducts curve towards the midline of the body and open separately into the bursal canal. The latter communicates with the atrium which receives the secretion of shell glands ectally to the openings of the oviducts. The bursal canal is lined with a nucleate, ciliated epithelium and is surrounded by a layer of circular muscles. The bursal canal communicates with a small copulatory bursa which is lined with vacuolated cells. In some animals the bursa cummunicates with the intestine, in others it does not so.
At about the point where each oviduct arises from the ovary it meets a narrow duct which curves towards the mid-ventral surface of the body. Half-way between the two ovaries the two ducts unite to form a common and still narrow part which runs backwards for some distance. This part may be surrounded by a thin layer of circular muscles. Subsequently, this narrow common duct communicates with the broad spermiduct that runs between the pharynx and the ovaries. In front of the pharynx the spermiduct bifurcates, giving of a branch on either side of the pharyngeal pouch. Each of these branches communicates with a lateral bursa. The spermiducts are lined with tall, highly vacuolated and nucleate cells. Usually, the lumen of the ducts as well as the vacuoles of the lining epithelium contain sperm.
The lateral bursae are large, elongate and somewhat sinuously folded sacs, one on either side of the atrium. They open ventrally to the exterior in such a way that their openings (almost) coincide with that of the gonopore. From that point the lateral bursae run anteriad up to the level of the base of the penis papilla; the anteriormost part of each bursa communicates with the spermiduct through a very short and narrow connecting duct, which actually represents a highly constricted part of the lateral bursa. The lateral bursae are lined with tall or cuboidal, nucleate and ciliated cells and they are surrounded by a well-developed layer of intermingled muscle fibres. In some animals only the posterior part of the lateral bursae (i.e. the part nearest to the opening to the exterior) is lined with ciliated cells, cilia being absent in the anterior portion of the bursae. Numerous glandular elements surround the lateral bursae and discharge a granular secretion into the bursae.
Some differences exist between specimens in the way the spermiducts continue their course after they have communicated with the lateral bursae. In some animals the spermiduct extends for a short distance backwards beyond the point where it meets the lateral bursa. This situation has been described by Westblad (1952). However, in some of the very large specimens examined (BMNH 1938.11.4.181-184, 1988.2.23.7) the situation is developed to a much more extreme extent. In these animals the spermiduct, after having communicated with the lateral bursa, forms an interlocking system of ducts, making up a sort of reticulum around the bursa. This reticulum envelops the anterior end of the bursa or may even extend backwards to about half-way along the lateral bursa.
Eyes
Each pigment cup contains three retinal cells and a large global or oval-shaped lens.
Ecology
S. liouvilli has been collected from under stones in the intertidal zone (Hallez 1913, Nurse 1964, BMNH 1988.2.23.9-10) or from seaweed (BMNH 1938.11.4.181-184). The species has also been collected from depths varying from 7 to 38 m (Westblad 1952, Material Examined). S. liouvilli has been found on Petermann Island (65°10'S 64°10'W; Hallez 1911, 1913), Tierra del Fuego (59 49'S 68 17'W; Westblad 1952), Heard Island (Nurse 1964), South Georgia (Westblad 1952, Material Examined), Arthur Harbour (64°49'S 64°08'W; Material Examined), South Orkneys (Material Examined), Grunden Rocks (63°24'S 56°58'W; Material Examined).
Distribution
TYPE LOCALITY: Petermann Island, Antarctica (65 10'S 64 10'W). S. liouvilli has been found on Petermann Island (65 10'S 64 10'W; Hallez 1911, 1913), Tierra del Fuego (59 49'S 68 17'W; Westblad 1952), Heard Island (Nurse 1964), South Georgia (Westblad 1952, Material Examined), Arthur Harbour (64 49'S 64 08'W; Material Examined), South Orkneys (Material Examined), Grunden Rocks (63 24'S 56 58'W; Material Examined).
Material Examined
M.N.H.N.: Lectotype: (V8-a), Ile Petermann, Expdition Charcot, no.46, 1910, no.320 of the collection of Dr. J. Liouville, sagittal sections on 2 slides.
M.V.: G1231, Atlas Cove, Heard Island, 29.08.1949, sagittal sections on 3 slides.
B.M.N.H.: 1969.11.25.1, Arthur Harbour, Antarctica, 64°49'S 64°08'W, sagittal sections of hind end on 6 slides; 1938.11.4.181-184, South Orkneys, 31.01.1915, sagittal sections on 59 slides; horizontal sections on 22 slides; 1988.2.23.6, South Georgia, E. Cumberland Bay, 24.02.1926, sagittal sections on 12 slides; 1988.2.23.7, South Georgia, E. Cumberland Bay, 28.02.1926, horizontal sections on 9 slides; 1988.2.23.8, South Georgia, E. Cumberland Bay, 29.12.1926, 6 slides with serial sections; 1988.2.23.9-10, Antarctica, Hope Bay, Grunden Rocks (63°24'S 56°58'W), 24.09.1945, sagittal sections on 7 slides; 1988.2.23.9-10, transverse sections on 7 slides.
S.M.N.H.: S.S.P., South Georgia, Cumberland Bay, Maiviken, 9.05.1902, sagittal sections on 4 slides; transverse sections on 5 slides; S.S.P., Tierra del Fuego (54°49'S 68°17'W), 19.03.1902, sagittal sections on 7 slides; transverse sections on 15 slides.
Type Material
M.N.H.N.: Lectotype: (V8-a), Ile Petermann, Expdition Charcot, no.46, 1910, no.320 of the collection of Dr. J. Liouville, sagittal sections on 2 slides.
According to Hallez (1913) there were only three type specimens, viz. two animals from sample no.320 and one specimen from sample no.332. One specimen from sample 320 was still available from the M.N.H.N. and has been sectioned by Sluys; this specimen has been designated as the lectotype (Sluys 1989).