testis  

The statocyst with a single highly refractile statolith is located anteriorly and can often be seen in the dissecting microscope. In many species there are prominent glands that open through an anteroterminal pore; these are the frontal glands. In mature animals, eggs are easily detected as very large cells with a large nucleus. Discerning the testes usually requires higher magnification. They are normally located anterolaterally to the ovaries, but there are exceptions. There are many different types of male copulatory organs including a simple pore, a ciliated antrum, a muscular penis or a sclerotized stylet. A female gonopore is present in most, but not all species. Female accessory organs may be present in the form of a bursa for storage of allosperm. In some species the bursa is equipped with a bursal nozzle, a narrow passage through which allospermatozoa have to pass in order to fertilize the oocytes. Other features of importance for identification of acoels are pigment patterns, presence of a pharynx (in a small number of species), presence of symbiotic algae, and body shape and size.