Microplana nana Mateos, Giribet & Carranza, 1998

Fully stretched living specimens are about 8-10 mm long and 0.5 mm wide, while the two fixed specimens measured up to 4 x 0.7 mm. The mouth is set at 2.5 mm and the genital aperture at 3 mm behind the anterior tip of the body. The small ocelli are located at the anterior end; dorsal surface is greyish with darker spots all over the surface; anterior end darker; creeping sole white.

Epidermis and musculature. - The epidermis of the creeping sole is about 10 mm thick, its cilia are densely packed and about 3 mm long. The epidermis of the lateral and the dorsal body wall is about 15 mm thick and its cells are packaged with rhabdites which have the same height as the epidermal cells. Nuclei of the epidermal cells are between 5-7 mm in diameter and basal to central in the cells.

In the ventral part of the body, interior to the subepidermal circular and longitudinal muscle layers, and separated from these by a layer of parenchymal tissue, there is a well developed layer of longitudinal parenchymal muscles about 15 mm thick. This parenchymal muscle layer occurs only ventrally (Fig 5).

Nervous system. - The central nervous system consists of two large ventral nerve cords connected by several commisures lying between the parenchymal muscle layers and the vasa deferentia. These nerve cords fuse at the anterior part of the body.

Alimentary system. - The anterior ramus of the intestine runs forwards to within about 0.1 mm of the anterior tip of the animal, giving off several pairs of branched lateral diverticula. Both posterior rami extend to almost the hind end, each giving off several diverticula. The diverticula are lined with large columnar cells each about 100 mm long.

In the holotype the pharynx is about 0.5 mm long and 0.35 mm in diameter. It is externally lined by a ciliated epithelium 4 mm thick, the cilia being 2 mm long. This epithelium covers a longitudinal muscle layer of about 2 mm thick, followed by a 4 mm thick layer of circular muscle, a layer 100 mm thick of parenchymal tissue with glandular elements, a layer about 12 mm thick of circular and longitudinal muscle fibers. This is bounded internally by a non-ciliated epithelium 6 mm thick.

Male reproductive system. - Each of the approximately 10 pairs of testes (Fig 5) is oval to circular, about 100 mm in diameter. The testes are situated ventrally, dorsal to the nerve cords, extending from behind the ovaries to the pharyngeal region. The testes discharge medially and ventrally into the vasa deferentia (Fig 5).

The vasa deferentia are two visible ducts situated ventrally, lateral and slightly dorsal to each nerve cord, receiving on the way to the penis papilla the openings of some testes (Fig 5). Before entering the penis papilla, the vasa deferentia enlarge to form two independent false seminal vesicles (Fig 6), hereafter the vasa deferentia narrow again and at the base of the penis papilla they fuse to form the ejaculatory duct, the latter lined with a nucleated epithelium. Some expansions can be observed along the ejaculatory duct due to the accumulation of spermatozoa (Fig 3).

The penis papilla is a well developed long, conical structure consisting of loose tissue surrounded by circular and longitudinal muscle layers. The penial bulb is weakly muscular. The gonopore is situated ventrally and centrally to the atrium (Fig 3).

Female reproductive system. - The two ovaries are oval-shaped, about 125 mm high by 100 mm, and lie ventrally above the brain at about 0.3 mm from the anterior end of the animal (Fig 7). The oviducts run posteriorly just above the nerve cords to the level of the narrow female genital duct (Fig 3), opening independently into the latter(Fig 4). The oviducts give rise to numerous short, dorsal branches which are in contact with the vitellaria. The vitellaria are well developed and extend from the level of the ovaries towards the posterior end of the animal and fill much of the space between the intestinal branches. The cells of the vitellaria are large, vacuolated and with glandular cytoplasm. The oviducts are ciliated internally and have an external diameter of about 18 mm.

The female genital duct (Fig 8) is about 25 mm in diameter and 300 mm long and is lined with a 5 mm thick non-ciliated epithelium. The genital duct is surrounded by few muscle fibers and by many glands.