Round Worms, Flat Worms and Annelids Andrew Sahr

Characteristics  Roundworms:  Nemathelminths phylum  Range from microscopic to as long as 3.3 feet (1 meter).  Have a hard, sharp spear on their head, and some have bristles on the head  Protected by a flexible but strong, grooved body covering  A layer beneath this covering releases fluids that harden to form the covering  Bilaterally symmetrical

Cont.  The body has 3 tissue layers and a fluid-filled false body cavity, meaning the cavity is between the inner and middle layers rather than the middle layer and the outer layer, as it is in complex animals  Roundworms live in salt water, fresh water and the soil.  Many of them are harmful to man as they are parasites.

Roundworm Life Cycle  Starts as an egg in a feces of an animal  Another animal either eats that animal or the feces of that animal  Transfers into the animals own intestines  Molts into the lava  Larva migrates through the intestinal wall and into the lungs where its coughed up and swallowed once more  Once it returns to the larva it begins to mature as an adult.

Reproduction  Sexually  Most species have a separate male and female but some are hermaphroditic  Males are typically smaller  Females have ovaries for holding the egg  During the copulation, male protrudes one or more spicules out of the cloaca and insert them into genital pore of the female.

Reproduction Cont.  Amoeboid sperm cells are passed along the spicules into the female worm  Eggs can be either embryonated or unembryonated when passed by the female, which means that their fertilized eggs are not yet developed

Roundworms in our Area  Baylisascaris  Intestinal Raccoon roundworm  Effects animals, including humans  Mature in Raccoon intestine  Released eggs take 2-3 weeks to become infective  When we ingest them from soil or water they hatch into larvae inside us  Travel through the body  Affect our organs and muscles

Characteristics cont.  Flatworms: also known as flukes  Bilaterally symmetrical  Body has 3 layers of tissues with organs and organelles  Body contains no internal cavity  Possesses a blind gut (i.e. it has a mouth but no anus)  Has Protonephridial excretory organs instead of an anus

Cont.  Reproduction is mostly sexual as hermaphrodites  Mostly feed on animals and other smaller life forms  Some occur in all major habitats, including many as parasites of other animals  Bilaterally symmetrical

Life Cycle of Flatworms  Start as an egg  Passed out in the feces of a bird  Eaten by Whelks  Inside the larvae hatches the eggs and multiplies by budding  Leave and invade cockles  Infected cockles are eaten by the birds in which the flukes mature and lay there eggs

Reproduction  A flat worm is reproduced when it splits In two  It will immediately form a new flatworm  Hermaphroditic  Each individual produces sperm and egg  When two flatworms mate, they exchange sperm so both become fertilized.  can also reproduce asexually by transverse fission

Reproduction Cont.  The body constricts at the midsection, and the posterior end grips a substrate  body rips apart  Each half grows replacements of the missing pieces to form two whole flatworms  if one of these flatworms is cut in half, each half will regenerate into two separate fully- functioning flatworms

Flatworms in Our Area  Heterobilharzia americanum  Waterborne flatworm  Parasite  Affects mostly dogs and raccoons  Sexually reproduces in the intestines  Eggs are laid in there so they can be carried out through feces

Characteristics cont.  Annelids:  Bilaterally symmetrical  Body has more than two cell layers which are tissues and organs  Body possesses a through gut with mouth and anus  Has true closed circulatory system  Has no true respiratory organs  Lives in most environments  Feed a wide range of material  Reproduction normally sexual and gonochoristic or hermaphoditic  Includes earthworms and leeches

Life Cycle of Annelids, The Earthworm  Hermaphrodites.  When two earthworms mate  They lie together and cover themselves in sticky mucus  Pass sperm into each others bodies  Sperm makes the egg in each body grow  A thick ring of slime forms around each worm's body and as the earthworm wriggles forward  the ring with eggs inside it slips off and is left on the ground  The ring closes at both ends and becomes a hard cocoon that protects the eggs.

Cont.  The eggs hatch after two weeks if the weather is warm  They can take up to three months to hatch when it is cold  Usually one or two earthworms hatch out of each egg  The young worms are about 12 millimeters long and light pink in color  Earthworms are able to mate when they are twelve months old.

Reproduction  Asexual  by dividing into two or more pieces or by budding off a new individual while the parent remains a complete organism  Some reproduce all asexually, while some reproduce sexually as well  Leeches have never been seen reproducing sexually

Annelids in Minnesota  Earthworms  All terrestrial earthworms are not native to Minnesota  15 species have been identified so far  Glaciers would have killed any worms before the European settlements  First Earthworms probably arrived through soil and plants from Europe

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