The un-segmented worms

Earland 2

GENERAL CHARACTERISTICS 18,500 species Simplest animals with bilateral

symmetry Exhibit some cephalization Three germ layers (i.e.:triploblastic) Acoelomate: no mesodermal lined

cavity 3 classes parasitic, 1 class free-living

Chapter 22 5

(a) Digestive System(a) Digestive System

Gastrovascular CavityGastrovascular Cavity

PharynxPharynxPharynxPharynx

(b1) Excretory System(b1) Excretory System

Excretory CanalExcretory CanalExcretory CanalExcretory Canal

Excretory PoreExcretory PoreExcretory PoreExcretory Pore

(b2) Nervous System(b2) Nervous SystemNerve CordNerve CordNerve CordNerve Cord

BrainBrainBrainBrain

Because they are flat, flatworms have no specialized circulation or respiration.

They simply use diffusion across body wall.

In addition to diffusion, flatworms use protonephridia (simple kidney-like structure) to osmoregulate (control water balance). Within the protonephridia, there are beating cilia which draws fluid through. Because this looks like a flickering candle, these cells are dubbed flame cells.

Digestion: 1 way (like us!): Pharynx is on underside of flatworm and sucks food into the gastrovascular cavity. Intestine branches the length of the

flatworm, so digested food can be delivered to all body tissues

Reproduction: Most flatworms are simultaneous hermaphrodites. Each individual can function as both male and female. Although a single individual cannot fertilize itself.

Movement: Secrete mucus and use cilia on their epidermal cells to glide across bottom, as well as muscle contractions which allows them to twist and turn.

Class Turbellaria-planarians, free-living, non-parasitic, live in moist environments

Class Trematoda-flukes, parasites that absorb nutrients from the body of a host harming it, may have more than 1 host

Class Cestoidea-tapeworms, parasitic, live inside 1 or more hosts, contain flat segments each with reproductive organs

Earland 10

Class Turbellaria 16% of flatworms Most species are free living. Most live in marine environments Diet includes: bacteria, algae and

invertebrates Considerable powers of regeneration in

some species

Class Cestoda Endoparasites: Internal parasites Celebrity cestoda: Tapeworm Hosts are primarily vertebrates. Extremely high specialization for

parasitic lifestyle. No ciliated epidermis. No mouth, instead has scolex studded with

hooks and suckers. Scolex attaches to the intestinal wall

It is estimated that 135 million people are infected with tapeworms. Symptoms include: Nausea, weakness, loss of appetite, abdominal pain, diarrhea and weight loss

Most of the body is made up of repeating reproductive segments called proglottids.

A single proglottid may contain over 100,000 eggs!

 An intermediate host is required, such as a cow, fish or pig.

Schistosoma lay so many eggs in blood vessels of the intestine that blood vessels burst and eggs and blood are released into intestine.

NematodaRotifera

unknown common ancestor

Porifera

Cnidaria

Platyhelminthes Nemertea

the pseudocoelomates

Nematoda Rotifera

• There are 9 different phyla that are classified as pseudocoelomates.•We are only covering 2 phyla:

Nematoda Rotifera

Organ level of organization

Tissues are organized to for organs which are used to accomplish physiological functions

Triploblastic

3 Germ Layers

endoderm

mesoderm

ectoderm

3 Tissue Layers

gastrodermis

mesoderm

epidermis

“false” body cavityectoderm

mesoderm

endoderm

Gut

pseudocoelom

the pseudocoelom is lined by mesoderm on ONE side only

the pseudocoelom

• is a closed, fluid filled cavity• contains digestive, excretory, and reproductive structures• the fluid within acts as a circulatory system• the fluid within acts as a hydrostatic skeleton against which the muscles work

• with anterior and posterior ends

Bilateral Symmetry

Cephalization

• concentration of sensory organs in the head of the animal

• complete (they have an anus!)• some regional specialization

Digestive System

Circulation System

• no system (or organs)• performed by the pseudocoelom fluid

• each individual of a species has the same # of cells • growth occurs by cells getting bigger rather than dividing

Eutely

the roundworms

Most abundant living animals include the roundworms –closely related to insects than others.

Cylindrical and bilateral body, a complete gut and a false coelom filled by reproductive organs. Have flexible cuticle – undergo repetitive molting as it grows.

Free living sp that are decomposers and agricultural pests.

Others are parasites to humans, dogs and insects.

Roundworms-small, cylindrical worms with pointed heads and tapered tails

3 tissue layers Complete digestive tract with mouth and anus Digestion highly specialized Free-living and non-parasitic roundworms are

the most abundant but parasitic types are hookworm, pinworm, threadworm and trichinosis

Many are introduced through poorly cooked pork or walk barefoot in infected areas

Earland 28

Advanced gastrovascular cavity Tubular Two openings

Advanced sensory "ganglionic brain" Lack circulatory and respiratory systems Depend on diffusion for gas exchange Sexual reproduction Most are harmless - Some parasitic

Chapter 22 29

Life Style Free-living parasitic

Digestion complete system (have an anus) some regional specialization (e.g. an

esophagus)

Skeletal system- fluid in pseudocoelom acts as a hydrostatic

skeleton

Cuticle covers body (secreted by epidermis

&composed mostly of collagen)

functions as a primitive external skeleton

Movement– longitudinal muscles ONLY (results in “whiplike” motion)

– No external/internal cilia even sperm don’t have flagella

http://www.devgen.com/devpage/largeimage/wild.html

Nervous system- cephalization, cerebral ganglia- dorsal and ventral nerve cords

Circulatory system– No system (no organs)– performed by fluid in pseudocoelom

Excretion – Renette glands

Reproduction

Sexual

usually dioecious often the sexes are sexually dimorphic

(males and females look different)

Males often have a spicule at the end of their tail used to insert their sperm into the female

Reproduction

Sexual usually dioecious often the sexes are sexually dimorphic internal fertilization males have ameboid sperm

• There are >12,000 species that are found in almost all habitats (marine, freshwater, underground, inside plants and animals, etc…).

• They are also incredibly abundant. For example:

• a m² of soil may contain >4 million nematodes

• a decomposing apple may contain >90,000 nematodes of a single species

• Many nematodes are important parasites of both plants and animals.

parasite of soybean plants

parasite of tomato plants

Eye worm (Loa loa):• transmitted by fly bites• larvae go through bloodstream • adults live in subcutaneous tissue

Intestinal roundworm (Ascaris):• transmitted by contaminated food• adults live in small intestine• it’s estimated that 20% of world’s population is infected (~1.3 billion people)

this intestine was completely blocked

Guinea worm (Dracunculus medinensis):• transmitted by infected copepods in drinking water • larvae move into the body cavity• female adult migrates to the subcutaneous tissue, causes an ulcer/blister, and releases eggs through hole when host comes in contact with water

Guinea worm (Dracunculus medinensis):

• traditionally removed by winding the worm around a matchstick over the course of several days• this may be the basis for the Caduceus symbol used in the medical field

Trichinella spiralis:• causes Trichinosis• transmitted by eating undercooked pork• juveniles encyst within host muscle cells

juvenile

Host muscle cell

ParasitesHeartworms (Dinofilaria immitis):

• The study of the model nematode C. elegans has resulted in important discoveries in genetics and development.

the rotifers

The “wheel” animals

Feeding have a “crown” of cilia called a corona the corona creates a

current to bring food into the mouth

Feeding have a specialized feeding structure called

the:

mastax-trophi complex

a modified muscular pharynx

modified jaws within the mastax

Some of the trophi (jaws):

Life Style Free-living

Digestion complete system (have an anus) some regional specialization (e.g.

mastax-trophi complex)

Skeletal system- fluid in pseudocoelom acts as a

hydrostatic skeleton

Movement– the corona – pedal glands (produce adhesive), as

well as foot and toe (spurs) for attachment to substrate

Nervous system- cephalization, cerebral ganglia- dorsal and ventral nerve cords

Circulatory system– no system (no organs)– performed by fluid in pseudocoelom

Excretion – protonephridia and flame cells– cloacal bladder (collects wastes)

Sexual Reproduction

- complex life cycle with different types of eggs- usually dioecious but in some groups, males

are absent (parthenogenesis)- Parthenogenesis:

unisexual reproduction where females produce offspring from unfertilized eggs (virgin birth)

AMICTIC EGGS MICTIC EGGS

• diploid (mitotically produced)

• can’t be fertilized

• develop into diploid, amictic females

• haploid (meiotically produced)

• produced after some sort of environmental stimulus (eg. high density, change in temperature)

if unfertilized, develop into haploid males

if fertilized, secrete a thick, protective shell until the environment is favorable again, after which they develop into diploid, amictic females

• There are ~1500 species. Although they are found mainly in freshwater habitats, there are a few marine rotifer species and a couple of species are even found in mosses!

• Because of the reduced role of males in reproduction, most males are incapable of feeding and do not even have a digestive tract (they are just there for sperm delivery!).

• Males have never been recorded in Bdelloid rotifers. This means they haven’t had sex in millions of years!

Loricifera

Priapulida

Kinorhyncha

Nematomorpha

Acanthocephala

Entoprocta

Gastrotricha

unknown common ancestor

Porifera

Cnidaria

Platyhelminthes Nemertea

NematodaRotifera

triploblasticorgan level of organization

mastax-trophicorona

pseudocoelomno cilia

longitudinal muscles only

complete digestive system