Download Directed movement evolved with anterior sense organs

Ch 10 Acoelomate
Bilateral Animals
Acoelomate Bilateral Animals
• Consist of phyla:
– Phylum Platyhelminthes
– Phylum Nemertea
– And others
Acoelomate Bilateral Animals
1. Simplest organisms to
have bilateral
symmetry
2. Triploblastic
3. Lack a coelom
4. Organ-system level of
organization
5. Cephalization
6. Elongated, without
appendages
Reproductive and
osmoregulatory systems
Bilateral Symmetry
• Divided along sagittal plane into two mirror
images
– sagittal= divides bilateral organisms into right
and left halves
• Anterior= head end
• Posterior= tail end
• Dorsal= back side
• Ventral= belly side
Bilateral animals
• Bilateral symmetry = important evolutionary
advancement
– Important for active, directed movement
• Anterior, posterior ends
– One side of body kept up (dorsal) vs. down
(ventral)
Directed movement evolved with anterior
sense organs cephalization
Cephalization
– specialization of sense organs in head end of
animals
• Acoelomates lack a true body cavity
– Solid body
– no cavity b/w the digestive tract and outer
body wall
Acoelomates are triploblastic
• Triploblastic (3 germ layers)
– Germ layer= layers in embryo
that form the various tissues
and organs of an animal body
3 germ layers
• Ectoderm
– Outermost germ layer
– Gives rise to outer covering of animal ie. epidermis
• Endoderm
– Innermost germ layer
– Gives rise to inner lining of gut tract
• Mesoderm
– Middle germ layer
– b/w ectoderm and endoderm
– Gives rise to various tissues/organs (ie. muscles)
Acoelomate animals have an
organ-system level of
organization
Acoelomate animals have an organsystem level of organization
• Organ-system
– Different organs
operate together (ie.
excretory system,
nervous system)
– mesodermal tissue
gives rise to
parenchyma
Digestive tract and
nervous system
Polyclad
• From Red Sea
http://www.rzuser.uni-heidelberg.de/~bu6/
Phylum Platyhelminthes
Flatworms
Free living
Parasitic
• From Atlantic ocean
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Phylum Platyhelminthes
• Flattened
dorsoventrally
– flatworms
• 34,000 species
• Gastrovascular cavity
(if present) has only
one opening (mouth =
anus)
• Mostly monoecious
Phylum Platyhelminthes
• First phylum that has an Organ
systems present
– derived mesodermally (parenchyma):
• Muscular system
• Digestive system (incomplete; gastrovascular
type) (absent in some)
• Nervous system
• Excretory system (absent in some)
• Reproductive system
Phylum Platyhelminthes
• Organ systems absent:
– Circulatory
– Respiratory
Rely on diffusion
Phylum Platyhelminthes (cont’d)
• Divided into 4
classes:
– Class Turbellaria
(mostly free-living
flatworms)
– Class Cestoda
(tapeworms)
– Class Trematoda
(parasitic flukes)
– Class Monogenea
(parasitic flukes)
Hymenolepsis- rat tapeworm
Class Turbellaria
• Mostly free-living
flatworms
• Marine (mostly) or
freshwater bottomdwellers
• Predators and
scavangers
• First group of
bilateral
symmetrical animals
Class Turbellaria (cont’d)
• Move by muscles, ciliated epidermis
Class Turbellaria (cont’d)
• Freshwater
turbellarians adapted
osmoregulatory
structures
– Protonephridia
• protos= first
• nephros= kidney
• network of fine tubules
running down sides of
organism
Class Turbellaria (cont’d)
– Flame cells= branch
from tubules
• Ciliary projections
drive fluid down
tubule
– Tubules open to
outside=
nephridiopore
Class Turbellaria (cont’d)
• nervous system with nerve ganglion
– ganglion- aggregation of nervous tissue
• Cephalization- cerebral ganglion= primitive brain
Class Turbellaria (cont’d)
• Ocelli= light-sensitive eyespots
Turbellarian Reproduction
• Asexual (fission)
– transverse
• Sexual
– Monoecious
(mostly)
– Cross-fertilization
Reproductive and
osmoregulatory
systems
Other 3 classes:
– Class Trematoda
– Class Cestoda
– Class Monogenea
• All parasitic
• lack cilia
• Have unusual body
covering: tegument
• Outer zone of tegument
(glycocalyx)
• consists of proteins
and carbohydrates
• aids in transport of
nutrients, waste, gases
• Protection against host
defenses
Class Trematoda
• Parasitic flukes
• Endoparasites
– Hooks, suckers,
increased
reproductive capacity
•
1mm-6cm long
•
Complex life
cycle:
1. Definitive host
(primary/final
host)
–
–
where parasite
matures and
reproduces
(sexually) (eggs
released)
vertebrate
2. Intermediate
host
–
Mollusc (ie. snail)
–
Hosts in which
larval stages
develop and
undergo asexual
reproduction
–
Results in an
increase in the
number of the
individuals
• Class Trematoda
– Example: Chinese Liver Fluke
Chinese Liver Fluke
• Infects 30 million
people in eastern
Asia
• Lives in ducts of
liver
– Eats epithelial
tissue, blood
• Definitive host:
– Humans, dogs,
cats
• 2 intermediate
hosts:
– snail
– fish
Class Cestoda
• Tapeworms
• Endoparasites
• Vertebrate host
– Live in digestive
tract
• 1 mm- 25m long
(EWWWW!!)
Hymenolepsis- rat tapeworm
Class Cestoda
• Highly
specialized
• Lack mouth,
digestive tract
– Absorb nutrients
across body wall
• Hooks and
suckers
– “head”= scolex
Hymenolepsis- rat tapeworm
• Adult tapeworms consist of long series of
repeating units= proglottids
• Chain of proglottids= strobila
• Tapeworms are monoecious (mostly)
– Mostly cross-fertilization
• No specialized sense organs
scolex
• Cestodes depend
on host digestion
– Small molecules
in host intestine,
liver
Beef Tapeworm
• Definitive
host= human
• Intermediate
host= cattle
Class Monogenea
• Parasitic flukes
• Mostly ectoparasites
• Single host, mostly
fish
Phylum Nemertea
• Triplobastic, acoelamate
•
bilateral symmetry
• Unsegmented
• Ciliated epidermis
• Closed circulatory
• usually <20cm
• Marine mud, sand
• Elongate, flattened
worms
Phylum Nemertea (cont’d)
• Unlike the platyhelminthes, Complete
digestive tract, with anus
– One-way
– More efficient; allows larger growth
Phylum Nemertea (cont’d)
• Cerebral ganglion, longitudinal
nerve cords
• Long proboscis used in
carnivorous species
• Two lateral blood vessels yet
no heart
• Dioecious
– “two” “house”
– Male and female organs in
separate individuals