26.4 Guided Notes


Chapter 26: Sponges, Cnidarians, and Unsegmented Worms Section 4: Unsegmented Worms Unsegmented Worms

____________________________________ have bodies that are not divided into special segments o Phylum ______________________________ o  Consists of simple animals called _________________ Phylum _______________________  Consists of long, thin worms called ________________


The members of the phylum Platyhelminthes are the simplest animals with _________________________________

Most members of this phylum exhibit enough ___________________________, or development of the

anterior end, to have what we call a _______________  Many flatworms are no more than a few millimeters thick, although they may be up to 20 meters long  Flatworms have more developed ____________________________ than either sponges or cnidarians

Form and Function in Flatworms

 Flatworms feed in either of two very different ways  Worms may be __________________________ that feed on tiny aquatic animals  Free-living flatworms have a _______________________________ with one opening at the end of a muscular tube called a _________________  They use the pharynx to suck food into the gastrovascular cavity  The gastrovascular cavity forms an intestine with many branches along the entire length of the worm  In the intestines, _______________________ help break down the food into small particles

 These particles are taken inside the cells of the intestinal wall, where digestion is completed  Like Cnidarians, flatworms expel undigested material through the _________________  Many other flatworms are ___________________________ that feed on blood, tissue fluids, or pieces of cells inside the body of their host  In many parasitic flatworms, the digestive tract is simpler than in free living forms  _________________________, which live within the intestines of their host, do not have any digestive tract at all  They have ____________________________________ with which they latch onto the intestinal wall of the host  From this position, they can simply absorb the food that passes by – food that has already been broken down by the host’s digestive enzymes  Flatworms lack any kind of specialized circulatory or respiratory system  Freshwater flatworms such as planarians have structures called __________________________ that help them get rid of extra water  Free-living flatworms have nervous systems that are much more developed than those of cnidarians and sponges  They have a definite head in which a _________________________ is located  One or more long nerve cords run from the brain down the length of the body on either side  Many flatworms have one or more pairs of light-sensitive organs called ___________________, or eyespots  The nervous system of free-living flatworms allows them to gather information from their environment – information that they use to locate food and to find dark hiding places  Parasitic flatworms often do not have much of a nervous system  Free-living flatworms usually use two means of locomotion at once o _____________________ on their epidermal cells help them glide through the water

o ______________________________ controlled by the nervous system allow them to twist and turn so that they are able to react to environmental conditions  Reproduction in free-living flatworms can be either sexual or asexual  Most free-living flatworms are ______________________________  The eggs hatch within a few weeks


 The free-living flatworms belong to the class ____________________  Most familiar members of this class are planarians  Turbellarians vary greatly in color, form, and size  Although most Turbellarians are less that 1 cm in length, some giant land planarians, which are found in moist tropical areas, can attain lengths of more than 60 cm


 Class ________________________ contains parasitic flatworms known as flukes  Most flukes are internal parasites that infect the blood and organs  These flukes have complicated life cycles that involve at least two different ___________________________  Blood flukes are found primarily in Southeast Asia, North Africa, and other tropical areas  ___________________ are the primary hosts of blood flukes  Most flukes are hermaphrodites and undergo sexual reproduction in a manner similar to that of free-living flatworms  Flukes produce many more eggs than free-living flatworms  Blood flukes lay so many eggs that the tiny blood vessels of the host’s intestine break open  The broken blood vessels leak both blood and eggs into the intestine  The eggs are not digested by the host and thus become part of the _________________  In developed countries, where there are toilets and proper sewage systems, these eggs are usually destroyed in the sewage treatment process

 But in many undeveloped parts of the world, human wastes are simply tossed into streams or even used as fertilizer  Once the fluke eggs get into the water, they hatch into _________________________________  When these larvae find a snail of the correct species, they burrow inside it and digest its tissues  The snail is an _________________________________ for the fluke  In the intermediate host, the flukes reproduce asexually  The resulting new worms break out of the snail and swim around in the water  If they find a human, the worms bore through the skin and eat their way to the blood vessels  In the blood, the get carried around through the heart and lungs to the intestine, where they live as adults  People infected with blood flukes get _________________________  They become weak and often die – either as a direct result of the fluke infection or because they cannot recover from other diseases in their weakened condition


 Members of the class _______________________ are long, flat parasitic worms that live a very simple life  They have a head called a __________________ on which there are several suckers and a ring of hooks  These structures attach to the intestinal walls of humans and other animals  Adult human tapeworms can be up to 18 meters long  Tapeworms almost never kill their host  Behind the scolex of the tapeworm is a narrow neck region that is constantly dividing to form many __________________________, or sections, that make up most of the body of the tapeworm

 The youngest and smallest proglottids are at the anterior end of the tapeworm  Male and female reproductive organs are contained in the proglottids  If food or water contaminated with tapeworm eggs is consumed by cows, pigs, fish, or other intermediate hosts, the eggs enter the intermediate host and hatch into larvae  These larvae grow for a time and then burrow into the muscle tissue of the intermediate host and form a dormant protective stage called a ______________  If a human eats raw or incompletely cooked meat containing these cysts, the larvae become active within the human host  Once inside the intestine of a new host, they latch onto the intestinal wall and grow into __________________________


Members of the phylum ________________________, which are known as roundworms, are among the simplest animals to have a digestive system with two openings – a mouth and an anus

Food enters through the mouth, and undigested food leaves through the anus

 Roundworms may be the most numerous of all multicellular animals  A single rotting apple can contain as many as ___________________ roundworms

Form and Function in Roundworms

 Most roundworms are _________________________  All roundworms have a long tube-shaped digestive tract with openings at both ends  Any material in the food that cannot be digested leaves through an opening called the _____________  Roundworms breathe and excrete their metabolic wastes through their body walls  They have no ____________________________________

 Roundworms have simple nervous systems  They have several ganglia in the head region but no definite brain  Roundworms reproduce ________________________  Fertilization takes place inside the body of the female How Unsegmented Worms Fit into the World  Do not have a lot of positive influence on humans  Responsible for some of the most painful and horrific diseases known o o ________________________ ________________________ o ________________________