the un-segmented worms. earland2 general characteristics 18,500 species simplest animals with...
TRANSCRIPT
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