Chapter 26: Sponges, Cnidarians, and Unsegmented Worms
Section 4: Unsegmented Worms
Unsegmented Worms
 ____________________________________ have bodies that are not divided into special segments o Phylum ______________________________
 Consists of simple animals called _________________ o Phylum _______________________
 Consists of long, thin worms called ________________
Flatworms
 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 freeliving 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
Planarians
 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
Flukes
 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
Tapeworms
 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 __________________________
Roundworms
 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 ________________________