Diagnosis: Synsiphonium ernesti (Hyman, 1958) can be recognized by its characteristic pattern of yellow patches on the dark dorsal body surface. With respect to anatomical features, the species is characterized by spermiducts of which the single anterior branch communicates with the ovaries through a branched, narrow duct. Other characteristic features are the glandularized septa projecting into the penis lumen, and the three eye lenses.
Habitus: Preserved specimens up to 5.5 mm long and 2.25 mm wide; according to Nurse (1964) they may even reach a length of 7 mm and a breadth of 3 mm. The animals are elongate oval-shaped with broadly rounded front and hind end. The largest diameter of the body is at about the hind end of the pharyngeal pocket.
The ventral surface of the body is unpigmented. The dorsal body surface is black-brown, except for the body margins and a number of yellowish patches. Such a patch occurs along the anterior body margin and extends as a yellow-brown stripe between the eyes, the stripe being bounded by somewhat darker coloured parts, as compared with the rest of the dorsal body pigmentation. At the level of the eyes there are two large, yellowish patches, the eyes being situated at their median margins. The posterior portion of the eye-patches may extend backwards for some distance in the form of narrow, tapering stripes. In other specimens the eye-patches extend backwards in the form of two long and broad bands. The eyes are very small and often obscured in the preserved specimens.
In the middle of the dorsal surface is situated a broad, more or less rectangular patch, and half-way this patch and the posterior body margin there is a small oval-or triangular-shaped spot on either side of the mid-dorsal line. From the posterior body margin arises an elongate patch which extends anteriad to about half-way the distance between the posterior margin and the two small yellowish spots.
The pharynx is one-fifth to one-third of the body length. The inner circular muscle layer of the pharynx is much thicker than the outer one, although the last-mentioned layer is also well developed. The mouth opening is situated at the hind end of the pharyngeal cavity.
The anterior ramus of the intestine extends, unbranched, anterior to the eyes. Behind the eyes this ramus gives off four lateral diverticula. Each posterior ramus gives rise to about 8-12 lateral diverticula. At the level of the pharyngeal pocket and also behind it, the posterior rami give off a few medially directed diverticula. The posterior gut trunks do not communicate.
Male Reproductive System
There are 15-20 testicular follicles on either side of the body, extending from directly behind the ovaries up to the level of the copulatory apparatus. The large, rounded or pear-shaped follicles are situated dorsally.
Already in front of the pharynx the vasa deferentia enlarge to form rather broad ducts which may expand, to greater or lesser extent, behind the pharyngeal pocket to form broader ducts or even may give rise to accessory seminal vesicles. Before penetrating the penis bulb, the vasa deferentia usually decrease somewhat in diameter, especially in cases where they had formed accessory seminal vesicles. After having penetrated the bulb, the vasa deferentia may increase again in diameter, thus giving rise to a sort of seminal vesicle. The extent to which the vasa deferentia enlarge in the last-mentioned situation, may differ between specimens. Inside the penis the vasa deferentia run side by side and unite in the intrapenial papilla, thus giving rise to a short common vas deferens, which opens at the tip of the intrapenial papilla. The section of the vasa deferentia running through the penis, is surrounded by a thick circular muscle layer; the common vas deferens is surrounded by a thinner layer of circular muscles.
The penis consists of a moderately muscularized bulb and a short or more elongate conical papilla, running almost parallel to the body surface. The ejaculatory duct houses a number of radially arranged septa which arise from the basis of the penis papilla (cf. Hyman 1958: Fig.3). The central column from which these septa radiate, houses the vasa deferentia and the common vas deferens, and thus forms the intrapenial papilla. The septa are traversed by well developed, longitudinal muscle fibres and delimit a number of chambers which are lined with a glandular epithelium. Apart from the septa, glandular epithelium also lines the ejaculatory duct.
The lining epithelium of the ejaculatory duct is underlain by a well developed layer of irregularly arranged, more or less circularly running, muscle fibres. This layer, however, could not be discerned in all specimens examined. The low, nucleate epithelium which covers the penis papilla, is underlain by a thick layer of circular muscles, consisting of several rows of fibres. This circular muscle layer is entally bounded by a thin layer of longitudinally running muscle fibres. Both muscle layers are continuous with those around the spacious male atrium.
Female Reproductive System
The vitellaria are well developed and extensive. They extend from anterior to the ovaries into the hind end of the body, and reach from dorsal to ventral body surface.
The ovaries are situated directly behind the brain, medially to the ventral nerve cords. The ovaries are more or less rounded follicles of which the postero-ventral surface shows a constriction, dividing each ovary into a large frontal part and a smaller posterior part. Just in front of this constriction the oviduct arises from the ventro-lateral surface of the ovary. The opening of the oviducts into the ovaries is closed by a clump of cells within the female gonads. In running backwards, the oviducts stay laterally to the ventral nerve cords. The oviducts could not be followed all the way from ovaries to female copulatory apparatus in every specimen examined. In a number of specimens the oviducts terminated at a short diatance behind the ovaries and could only be found again close to the point where they open separately into the distal portion of the bursal canal.
At about the point where the oviducts arise from the ovaries they communicate with small ducts which unite at a short distance behind the gonads to form a common section. This common, but still narrow, duct communicates with the broad spermiduct branch that runs between the ovaries and the root of the pharynx. These small ducts, including their common section, are surrounded by a circular muscle layer, and their openings into the ovaries and the spermiduct are surrounded by a well-developed zone of circular muscle fibres.
The spermiduct branch enlarges to form a globular expansion just in front of the root of the pharynx. This expansion bifurcates, giving off a spermiduct branch on either side of the pharynx. All three spermiduct branches are devoid of any surrounding musculature. The lining of the spermiduct branches consists of large, cuboidal cells with very large vacuoles. The spacious lumen of the spermiduct branches and the vacuoles of the lining cells usually contain sperm.
At about the level of the gonopore, the posterior branches of the spermiduct communicate, via a considerable narrowing, with the anterior portion of the lateral bursae. These bursae are elongate vesicles of which the proximal section curves anteriad and the distal section opens ventrally to the exterior. The openings, on either side of the body, are situated at the level of the gonopore or slightly behind it, and are located just medially to the ventral nerve cords. The lateral bursae are lined with cuboidal, nucleate cells bearing well developed cilia. The bursae are surrounded by a well developed layer of interwoven muscle fibres, while an erythrophilous secretion is discharged into the bursae.
The remaining part of the female reproductive system consists of a female atrium, bursal canal, and copulatory bursa. The female atrium is spacious and communicates with the male atrium but is set off from the latter by means of a weak constriction. The female atrium may function as a female genital duct but its histology does not differ from that of the male atrium, apart from the fact that the former receives the numerous openings of shell glands.
The posterior portion of the female atrium communicates with a short and broad bursal canal. The ciliated cells lining the canal are nucleate. The bursal canal is surrounded by a circular muscle layer. The canal curves dorsally and meets a small, rounded copulatory bursa, which is lined with large, vacuolated cells. The bursa does not have any connection with the intestine and is devoid of any surrounding musculature.
The eye cups contain three retinal cells, which are covered by three lenses.
S. ernesti has been found under stones (Hyman 1958; Material Examined: ZMA V.Pl.826), and in rock pools (Nurse 1964, Material Examined: W5568). The species has been collected also from algal scrapings and from among bryozoa (W5584, W5566) and from holdfasts of the bull kelp Durvillea (Sluys and De Vries 1988).
Type locality: Buckles Bay, Macquarie Island, Australia. The species is known from Macquarie Island, Possession Island, and Saunders Island (West Falklands).
Material Examined and Type Material
Type material of Miava ernesti. S.A.M.: V3127, Buckles Bay, Macquarie Island, 12.03.1930, 1 slide with 7 whole mounts; V3128, ibid., sagittal sections on 2 slides.
Type material of Palombiella macquari. M.V.: Holotype, G1220, Macquarie Island, Aerial Cove, 26.01.1950, sagittal sections on 2 slides. Paratypes: G1486 (=G1221 B), Macquarie Island, Garden Cove, 28.12.1948, transverse sections on 9 slides; G1487 (=G1221 C), , sagittal sections on 5 slides.
A.M.: W5566-1, Macquarie Island, Buckles Bay, Garden Cove, 23.03.1968, sagittal sections on 3 slides; W5566-2, sagittal sections on 3 slides; W5566-3, sagittal sections on 3 slides; W5566-4, sagittal sections on 4 slides; W5566-5, sagittal sections on 3 slides; W5566-6, sagittal sections on 3 slides; W5566-7, transverse sections on 5 slides; W5568-1, Macquarie Island, Buckles Bay, 15.09.1968, sagittal sections on 3 slides; W5568-2, sagittal sections on 4 slides; W5568-3, horizontal sections on 3 slides; W5584-1, Macquarie Island, Hasselborough Bay, Cosray Rocks, 1.06.1968, sagittal sections on 8 slides, W5584-2, , sagittal sections on 7 slides; W6013-1, Macquarie Island, north Garden Cove, 18.11.1968, sagittal sections on 4 slides; W6013-2, sagittal sections on 4 slides.
M.N.H.N.: AJ 781.1, Crozet Islands, Possession Island, Baie du Navire, 20.04.1974, sagittal sections on 2 slides; AJ 781.2, sagittal sections on 2 slides; AJ 781.3, sagittal sections on 2 slides; AJ 783.1, sagittal sections on 3 slides; AJ 785.2, sagittal sections on 5 slides; AJ 785.3, sagittal sections on 2 slides; AJ 785.4, sagittal sections on 3 slides; AJ 785.6, sagittal sections on 3 slides.
Z.M.A.: V.Pl.826.1, Saunders Island (West Falklands), 26.12.1986, horizontal sections on 2 slides; V.Pl.826.2, horizontal sections on 2 slides; V.Pl.826.3, horizontal sections on 1 slide; V.Pl.826.4, sagittal sections on 4 slides; V.Pl.826.5, sagittal sections on 3 slides; V.Pl.826.6, sagittal sections on 3 slides; V.Pl.826.7, transverse sections on 4 slides; V.Pl.826.8, transverse sections on 6 slides; V.Pl.826.9, transverse sections on 4 slides.