Marcus, 1947
Overview
Diagnosis: With respect to external features D. divae may be recognized easily by its body shape and the distinct markings on the back. The most characteristic anatomical features are the extra-bulbar common vas deferens and the common oviduct that opens directly into the female atrium.
Habitus: Live specimens about 3 mm long and 0.6 mm wide (Marcus 1947); the whole mounts examined were much smaller, viz. 1.5 x 0.55 mm and 1.3 x 0.35 mm. The body of living animals is torpedo-shaped, i.e. the body margins taper to a highly pointed hind end, and the front end is rounded or obtusely pointed. Living specimens show a conspicuous constriction at the level of the eyes (Marcus 1947), but this feature did not show in the whole mounts examined. The ground colour of the body is white but the dorsal surface shows a dark, pigmented area around the eyes and two paramedian bands. The latter meet at the hind end of the body but do not reach the pigmented patch around the eyes, the bands terminating just behind the patch.
Alimentary System
The pharynx is between one-seventh and one-sixth of the body length and situated in the posterior half of the body. The outer circular muscle layer of the pharynx is comparatively thick and of about the same diameter as the inner circular muscle layer. The mouth opening is situated at the hind end of the pharyngeal pocket.
The anterior ramus of the intestine extends forwards between the eyes but is devoid of lateral branches. The anterior gut trunk gives rise to about seven pairs of post-ocellar diverticula. Each posterior intestinal ramus gives rise to about ten pairs of lateral diveticula; both trunks anastomose in the hind end of the body, while commissures may be present posteriorly to the copulatory apparatus. The lateral branches of the intestinal trunks are usually forked and anastomose at their tips, thus giving rise to an intricate, reticulate intestinal system (cf. Marcus 1947: Pl.19, Fig.79).
Male Reproductive System
The total number of testes is about 4 or 5. The small follicles are situated at the ventral body surface and lie between the ovaries and the root of the pharynx.
Behind the pharynx the vasa deferentia enlarge to form false seminal vesicles, which turn dorso-medially and unite to a common vas deferens just outside the penis bulb. Within the bulb the common vas deferens opens into a large seminal vesicle. Penis glands open into the latter vesicle, which empties via a constriction into the broad ejaculatory duct. The last-mentioned duct also receives the secretion of the penis glands.
The penis papilla has the shape of an elongate cone and has either an oblique, dorso-caudal orientation or runs parallel to the body surface; it is covered with a flat, nucleate epithelium. The papilla is provided with a relatively thick, subepithelial layer of circular muscles. The male atrium is lined with a high, nucleate epithelium.
Female Reproductive System
The vitellaria are extensive and well-developed. They extend from dorsal to ventral body surface, filling all the space between the intestinal diverticula, and occur from the level of the brain into the hind end of the body.
The small ovaries lie at a considerable distance behind the brain, i.e. between one-third and one-half of the distance from the brain to the root of the pharynx. Young, small oocytes are situated in the ventral portion of the ovaries. The oviducts arise from the ventro-lateral surface of the ovaries and follow their course backwards dorso-medially to the ventral nerve cords.
Behind the copulatory apparatus the oviducts unite to a short common oviduct which communicates with the female atrium (female genital duct), which is penetrated by the openings of extensively developed shell glands. The female atrium is lined with cubiodal, nucleate cells.
Eyes
The eyes show a distinct, globular lens; the number of retinal cells could not be determined.
Ecology
The species has been collected from among algae in the supra-littoral zone.
Distribution
Type locality: Ilha das Palmas, in the Bay of Santos, Brazil (23°02'S 43°13'W). The species is known only from the type locality.
Material Examined and Type Material
Two uncatalogued slides from Dept. Zoologia Sao Paulo, one slide containing two whole mounts of D. divae and one of Vatapa gabriellae, and on the second slide sagittal sections of one specimen (type material).
S.M.N.H.: a whole mount on 1 slide, and sagittal sections on 1 slide (type material).