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Marcus, 1963

Overview
Diagnosis: Tiddles evelinae Marcus, 1963 can be recognized easily by its two genital pores, the posterior one leading to a female genital duct which receives the separate openings of the oviducts and communicates with the atrium.
Habitus: Live specimens are up to 5 mm long and 0.4 mm wide, while preserved animals have a maximum length of 2.9 mm and a width of 0.39 mm (Marcus 1963). The body margins run parallel between the rounded anterior and posterior end. Dorsal and ventral surface are white.

Alimentary System
The pharynx is situated in the posterior half of the body and is between one-eighth and one-seventh of the body length. The inner circular muscle layer of the pharynx is much thicker than the outer zone of circular muscles. The mouth opening lies at the hind end of the pharyngeal cavity.
The long anterior ramus of the intestine terminates behind the brain and gives rise to about 15 pairs of lateral diverticula. Each of the posterior intestinal rami gives off about 9 lateral diverticula; the posterior gut trunks meet in the hind end of the body.

Male Reproductive System
The testes number very few: generally there is only 1 follicle on either side of the body, but sometimes up to 2-3 follicles are present on each side. The testicular follicles are situated ventrally half-way between the ovaries and the root of the pharynx.
The vasa deferentia enlarge to form false seminal vesicles which decrease in diameter when entering the very weakly developed penis bulb. Immediately after having penetrated the bulb the vasa deferentia open into a relatively large seminal vesicle which tapers to form the ejaculatory duct. This ejaculatory duct is lined with tall, nucleate cells and receives the openings of penial glands; the duct is surrounded by a layer of circular muscles.
The penis papilla is a stubby cone which is covered with a nucleate epithelium and is provided with a subepithelial layer of circular muscles, overlain with a layer of longitudinal muscle fibres.

Female Reproductive System
The vitellaria occupy the entire space between the dorsal and ventral body surfaces and extend from some distance behind the brain (but anterior to the ovaries) into the hind end of the body.
The ovaries are located at a considerable distance behind the brain, viz. between one-third and one-half of the distance between the brain and the root of the pharynx. The oviducts run lateral to the ventral nerve cords.
In the posterior end of the body the oviducts open separately into the distal, i.e. ventro-posterior, section of the female genital duct. The latter opens into the postero-dorsal portion of the atrium and has a separate, ventral opening to the exterior. The female genital duct is lined with nucleate cells and receives the secretion of abundant shell glands between the openings of the oviducts and the opening of the duct into the atrium.

Eyes
The eye cups are very small and probably contain only a single retinal cell, as was already suggested by Marcus (1963); a lens is absent.

Ecology
T. evelinae is only known from its type locality, where specimens were collected from a compost pile high in the tidal zone (Marcus 1963).

Distribution
Type locality: Cananéia (25°01'S 47°50'W), Brazil. T. evelinae is only known from its type locality.

Material Examined
S.M.N.H.: 1454-1, Cananéia, sagittal sections on 1 slide; 1454-2, horizontal sections on 1 slide; 1454-3, sagittal sections on 1 slide; 1454-4, sagittal sections on 1 slide (syntypes).

Type Material
Present location of the material sectioned by Marcus (1963) is unknown. The S.M.N.H. houses a jar (no.1454) with preserved type specimens, of which some have been sectioned, viz. 1454-1, Cananéia, sagittal sections on 1 slide; 1454-2, horizontal sections on 1 slide; 1454-3, sagittal sections on 1 slide; 1454-4, sagittal sections on 1 slide (syntypes).

Tiddles evelinae