Brown Planaria

• GeneralCut into pieces, each fragment grows back into a whole animal, head included.
• regeneraciónIt can regrow a whole animal from a tiny fragment of its body, and some studies suggest it may keep some memory after regrowing its head.
• It is one of the central models in research on regeneration and stem cells.
• Its eyes form no images: they detect only the direction and intensity of light, enough for it always to flee towards darkness.
• It regenerates a complete animal from a tiny fragment, head and brain included. It has been the classic model of regeneration since Thomas Hunt Morgan's experiments in the late nineteenth century.
• That ability rests on pluripotent stem cells called neoblasts, distributed throughout the body, which can become any cell type.
• It also reproduces by splitting itself in two: it anchors its front end, stretches the rear until it tears away, and each half regrows what it lacks.
• It has two eyespots that give it a cross-eyed look and that detect light without forming an image; it flees from light.
• It has no anus: the mouth is halfway along its underside, it extends its pharynx like a trunk to swallow, and expels the remains the same way.

Skeleton type

Invertebrate - no rigid skeleton (hydrostatic skeleton)

Habitat and environment

Streams, ponds and clean freshwater springs

Sources consulted: Wikipedia (en): Girardia tigrina