Diagnosis: Cercyra teissieri Steinmann, 1930 is characterized by the pigment pattern on its dorsal surface and by the fact that it is a fully dioecious species, i.e. the male and female reproductive organs are carried by different animals. Male animals show no traces of the female reproductive system and the reverse holds true for female animals.
Habitus: Living animals up to 3-4 mm long and 0.5-0.7 mm wide. The body is lanceolate with rounded front and hind end. The dorsal surface is provided with a number of irregularly shaped, dark brown patches. In front of the eyes, which lie at a considerable distance from the anterior body margin, a broad brown band runs between the lateral body margins. A narrow pigmented stripe may extend backwards between the eyes from the posterior surface of the above-mentioned band.
The pharynx is about one-sixth of the body length. The anterior ramus of the intestine does not extend anterior to the eyes and gives off 7-8 lateral diverticula. Each posterior ramus gives rise to 10-12 lateral diverticula; commissures may be present between both branches. The mouth opening lies at the hind end of the pharyngeal pocket.
There are about 20, dorsally situated, testes on either side of the body. The original species description does not mention whether or not the testes are distributed throughout the body length. Since no specific remarks are made, it may be assumed that the testes are distributed in a way that conforms to the situation in Cercyra hastata, i.e. that the follicles extend from behind the brain up to the level of the copulatory apparatus.
Immediately behind the pharyngeal pocket the two vasa deferentia unite to form a single, broad and winding vas deferens. The last-mentioned duct narrows while penetrating the penis and, subsequently, opens into a large seminal vesicle. From the posterior wall of this vesicle arises a narrow ejaculatory duct. The penis bulb is a large and highly muscularized structure which surrounds the seminal vesicle. The penis papilla is a pointed, chitinized cone. Penis bulb and papilla are more or less parallel to the body surface. The penis papilla projects into a spacious male atrium of which the posterior section tapers to a broad duct that curves ventrad and opens to the exterior via the gonopore.
The paired ovaries are situated at about half-way the distance between the eyes and the root of the pharynx; usually the follicles are somewhat closer to the eyes than to the pharynx. The globular female atrium is surrounded by a welldeveloped muscle layer (cf. Steinmann 1930: Fig. 3). Gland cells discharge their secretion into the atrium which communicates with the exterior through a duct that arises from its ventral surface.
The copulatory bursa is a very small, globular vesicle. From its ventral surface arises the bursal canal which, after a short ventrally running section, makes a sharp anteriorly directed bend before opening into the atrium. The bursal canal receives the separate openings of the oviducts shortly before communicating with the atrium.
Vitellaria occur everywhere between the intestinal diverticula.
No details are available on the histological structure of the eyes.
Life Cycle: Cocoons are laid during mid-summer.
Cercyra teissieri has been found on red algae near Roscoff, France.
Type locality: Roscoff, France. The species is known only from its type locality.
Material Examined, Type material
In a letter of Steinmann to Sixten Bock, dated 14 May 1940, the former mentions that 2-3 specimens of C. teissieri were deposited in the biological station in Roscoff. Unfortunately, the material is no longer available from this institution.
Since no new material has become available, this account on Cercyra teissieri is based on the original species description.