Download Flatworms, roundworms and rotifers

The sea jellies, flatworms
and rotifers
Tom Hartman
www.tuatara9.co.uk
Animal form and function 1
Module 11112
MCQs from handout 8
Another MCQ test
Evaluate the following statements:
1.
2.
3.
4.
5.
humans are triploblastic
there is one type of sponge that fishes for its prey
ctenophores have blind ended guts
nematocysts (cnidocysts) are captured from sea slugs
cnidocysts evert to puncture prey and deliver their stings
Animals
All other animals
(bilateralia)
Radiata
Sponges
Choanoflagellates
Fungi
The radiata
•
•
•
•
•
Radial symmetry
Two cell layers
Jelly sandwich (with some cells)
Nematocysts
Gut has one opening….
Phylum Ctenophora
• Radial symmetry
• Two cell layers with
gelatinous mesoglea in
which muscle fibres run.
• Eight rows of fused cilia.
• Muscular tentacles with
sticky spirocyst-like
organelles.
• Tissues but no organs.
• Complete gut!
• No polyp stage.
Phylum ctenophora
• One species found in the North Atlantic was
introduced accidentally to the Black sea (via
ballast tank flushing) where they became the
dominant predator of plankton.
• Caused the collapse of the anchovy fisheries.
• Biomass was estimated to be 1,000,000 tons!
• Accidental introduction of a predator has
reduced this (also a ctenophore).
• Pest species recently found in the Baltic,
Caspian and North seas.
Leaving the radiata
• Leading hypotheses agree on major
features of the animal phylogenetic
tree.
• Zoologists currently recognize
about 39 animal phyla.
• New levels of complexity.
Animal pole
Vegetal pole
New levels of complexity 1. Cleavage
• Cleavage is spiral and determinate =
protostome development
• Cleavage is radial and indeterminate
= deuterostome development
Protostome development
(examples: molluscs, annelids,
arthropods)
Eight-cell stage
Spiral and determinate
Deuterostome development
(examples: echinoderms,
chordates)
Animal pole
Eight-cell stage
Radial and indeterminate
Vegetal pole
All other animals
(bilateralia)
Deuterostomes
Protostomes
Animals
Radiata
Sponges
New levels of complexity 2.
Fate of the Blastopore
• In protostome (spiral cleavage) development
– The blastopore becomes the mouth
• In deuterostome (radial cleavage)
development
– The blastopore becomes the anus
Mouth
Anus
Digestive tube
Mouth
Mouth develops
from blastopore
Anus
Anus develops
from blastopore
New levels of complexity 3.
A new cell layer
• Triploblastic animals
• Blastocoel is ‘invaded
by cells as the gastula
matures.
• These mesenchyme
cells organise the
internal architecture
and some become the
mesoderm.
• Mesoderm spawns
organs and tissues
between the ‘skin’
and the ‘gut’.
Gastrulation in a sea urchin embryo
Key
Future ectoderm
Future mesoderm
Future endoderm
Blastocoel
Mesenchyme
cells
Vegetal
plate
Vegetal
pole
Animal
pole
Gastrulation in a sea urchin
embryo
Key
Future ectoderm
Future mesoderm
Future endoderm
Animal
pole
Blastocoel
Mesenchyme
cells
Vegetal
plate
Vegetal
pole
Blastocoel
Filopodia
pulling
archenteron
tip
Archenteron
Blastopore
Mesenchyme
cells
50 µm
Gastrulation in a sea urchin embryo
Key
Future ectoderm
Future mesoderm
Future endoderm
Animal
pole
Blastocoel
Mesenchyme
cells
Vegetal
plate
Vegetal
pole
Blastocoel
Filopodia
pulling
archenteron
tip
Archenteron
Blastopore
Mesenchyme
cells
Blastocoel
50 µm
Archenteron
Ectoderm
Mesenchyme:
(mesoderm
forms future
skeleton)
Mouth
Blastopore
Digestive tube (endoderm)
Anus (from blastopore)
Protostomes
All other animals
(bilateralia)
Ecdysozoa
Lophotrochozoa
Deuterostomes
Animals
Radiata
Sponges
Ecdysozoa
Insects, cruscatea, myriapods, arachnids
Protostomes
Velvet worms
Round worms
Lophotrochozoa
Strange bivalves
Snails, octopi, bivalves, etc.
Triploblastic
Bilateralia
Eumetazoa
Deuterostomes
Segmented worms
Flat worms
Wheel mouths
Lanclets, vertebrates, etc.
Starfish, urchins, etc.
Comb jellies
Radiata
Diploblastic
Parazoa
Anemones, hydras, etc.
Sponges
Layers
• Animal embryos
– Form germ layers, embryonic tissues,
including ectoderm and endoderm.
• Diploblastic animals
Ectoderm
– Have two germ layers.
• Triploblastic animals
– Have three germ layers:
mesoderm.
Endoderm
Adult derivatives of the three
embryonic germ layers in
vertebrates
ECTODERM
• Epidermis of skin and its
derivatives (including sweat
glands, hair follicles)
• Epithelial lining of mouth
and rectum
• Sense receptors in
epidermis
• Cornea and lens of eye
• Nervous system
• Adrenal medulla
• Tooth enamel
• Epithelium or pineal and
pituitary glands
MESODERM
• Notochord
• Skeletal system
• Muscular system
• Muscular layer of
stomach, intestine, etc.
• Excretory system
• Circulatory and lymphatic
systems
• Reproductive system
(except germ cells)
• Dermis of skin
• Lining of body cavity
• Adrenal cortex
ENDODERM
• Epithelial lining of
digestive tract
• Epithelial lining of
respiratory system
• Lining of urethra, urinary
bladder, and reproductive
system
• Liver
• Pancreas
• Thymus
• Thyroid and parathyroid
glands
Where on the tree?
Ecdysozoa
Insects, cruscatea, myriapods, arachnids
Protostomes
Velvet worms
Round worms
Lophotrochozoa
Strange bivalves
Snails, octopi, bivalves, etc.
Triploblastic
Bilateralia
Eumetazoa
Deuterostomes
Segmented worms
Flat worms
Wheel mouths
Lanclets, vertebrates, etc.
Starfish, urchins, etc.
Comb jellies
Radiata
Diploblastic
Parazoa
Anemones, hydras, etc.
Sponges
Or possibly
Ecdysozoa
Protostomes
Insects, cruscatea, myriapods, arachnids
Velvet worms
Round worms
Lophotrochozoa
Strange bivalves
Snails, octopi, bivalves, etc.
Triploblastic
Bilateralia
Platyzoa
Eumetazoa
Segmented worms
Wheel mouths
Flat worms
Lanclets, vertebrates, etc.
Deuterostomes
Starfish, urchins, etc.
Comb jellies
Radiata
Diploblastic
Parazoa
Anemones, hydras, etc.
Sponges
Flat worms
Phylum Platyhelmithes
•
1.
2.
3.
4.
5.
6.
7.
8.
Big changes from all animals branching
earlier.
Bilaterally symmetrical.
SuperTriploblastic in development.
phylum
Tissues and organs.
Bilateralia
Definite anterior end with cephalisation.
Simple nervous system and brain.
Many have eyes.
Muscular system/cilia for movement.
Free living and parasitic.
• Turbellarians
• Flukes
(trematodes)
– parasitic
• Tapeworms
(cestodes)
– parasitic
• No circulatory system
therefore:
• Flat to cope with O2/CO2
diffusion.
• Sac like or branched gut.
– Gut delivers nutrients in
absence of circulatory
system.
– Gut absent in some parasitic
forms
(a derived feature).
• A solid body: no cavities.
• Excretory/osmoregularity
organs (protonephridia).
A planarian in cross section
A solid body with no spaces or cavities: ACOELOMATE.
Parasites can have an
extraordinarily complex life cycle.
Generalised fluke life cycle
Reproduction
• Mostly hermaphrodite with complex
reproductive systems with some species reliant
on asexual reproduction: they tear in half!
• This has lead to some vital observations on the
nature of development and chemical gradients.
Regeneration in Planaria
End of lecture