Planaria and Their Regenerative Powers
An invertebrate, by definition, is an animal without a vertebra, what is more commonly
know as a backbone.
These organisms are very morphologically diverse and live in almost every
habitat in the world (Campbell and Reece, 2005).
Out of the 35 animal phyla described by
biologists, 34 describe invertebrates, and of all the described animal species known to man, 95%
are invertebrates (Campbell and Reece, 2005).
The invertebrate used in this study is a member
of the genus
, an organism in the phylum Platyhelminthes, more commonly known as
Platyhelminthes are triploblastic, acoelomates that are bilaterally symmetrical. These
organisms are free-living flatworms that generally live in freshwater ponds or streams and feed
on smaller animals such as small insects (Reddien and Sánchez Alvarado, 2004; Campbell and
Since the organisms in this phyla lack a coelom, they do not have a respiratory
system or a circulatory system, instead they respire via diffusion (Newmark and Sánchez
Planaria, family Planariidae (class Turbellaria), are very popular specimens in
scientific studies due to their regenerative capabilities
morphological features of Planaria are their two “eyespots” (photoreceptors) located on the
anterior, dorsal region (head) of the organism and the opening of the pharynx (mouth) located on
the ventral side of the body.
Planaria have the ability to regenerate, meaning when a piece of
their body is amputated the resulting two pieces “grow back” the lost pieces, creating new
Planaria (Lum and Shakhbandaryan, 2006).
Something to note is that the cells located just above
the photoreceptors and those located at the pharynx are not able to regenerate a complete animal