Answer to Question #325427 in Zoology for Gu²

Question

Provide a brief explanatory note to distinguish between planaria reproduction, regeneration and feeding

Answer 1

Planaria reproduce both sexually and asexually. There are two methods of asexual reproduction: fragmentation and sponta-

neous “dropping tails”. Fragmentation usually begins with a transverse constriction just behind the pharynx, which increases

until the two parts separate and move away from each other. The head grows a new tail, and the tail grows a new head. In

spontaneous “dropping tails”, planaria in very stagnant water will frequently “drop” their tails, and the tails regenerate to form

complete animals. This condition usually results in stunted animals, or dwarfs, which remain in this state until water condi-

tions improve.

Because planaria are hermaphroditic — each animal possesses complete male and female systems — they reproduce sexually

by producing “summer” eggs and “winter” eggs. Summer eggs are thin-shelled and transparent; winter eggs are usually black

and on stalks. While summer eggs hatch quickly, winter eggs take longer to hatch; they may even remain dormant through-

out the winter, and they are capable of withstanding unfavorable environmental conditions.

When Planaria is cut into pieces, each piece grows into a complete organism. This is the regeneration process which is carried out by the special cells. Also, regeneration is different from the reproduction. This is because most of the organisms do not depend on being cut in order to reproduce.

The planarian is a carnivore. To ingest (swallow) food, the planarian extends its pharynx out of its mouth. The pharynx is a muscular tube that is used by the planarian to swallow prey animals whole (in the case of small animals) or to suck in body juices of a larger animal.