Download Chapter 12 The Invertibrates

Chapter 12 The Invertebrates
zoology - the study of animals
General Characteristics of Animals
• multicellular
• eukaryotic
• heterotrophic - must obtain and ingest organic food.
Classification by notochord
The animal kingdom is divided into two broad groups:
• vertebrates - animals that posses a notochord (spinal chord) at
sometime in their life.
• invertebrates - animals that lack a backbone throughout their life.
Embryological Development in Animals
All life begins as a single cell (fertilized egg) and goes through certain
stages in it’s development to a multicellular organism:
Zygote - fertilized egg
multiple divisions
Blastula - a hollow ball of cells
formation of germ layers:
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• ectoderm - outer layer. Will become skin, nervous system, nails,
hair, scales
• endoderm - inner layer. Will become the lining of the gut
• mesoderm - middle layer. Will become internal organs and
muscles
gastrulation - an infolding on one side
Gastrula
The degree of complexity between animals depends on how much
the germ layers differentiate (become different types of cells). For
example:
• jellyfish and sponges have no mesoderm because they do not
develop internal organs or muscles. Water circulates freely
throughout them delivering nutrients directly to each cell and
carrying away waste at the same time. There is no need for a
transport system.
• complex animals have internal organs and transport systems in
order to get past the lack of water environment.
Classification by body cavity (coelom)
coelom – a lined body cavity which houses the internal organs
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acoelomate • no coelome
• flatworms (Platyhelminthes)
pseudocoelomate • false (fluid-filled) coelom
• round worms (Nematoda)
coelomate
• true body cavity lined with
peritoneum.
• vertebrates
Classification by symmetry - (the general body plan).
Can you get a mirrored image if you cut this thing down the middle?
• asymmetry - having no orientation of body plan - no
front/back/top/bottom. E.g. Sponges (Porifera)
• radial - having symmetry about a central axis. E.g.
Jellyfish, hydra (Cnidaria) and starfish (Echinodermata)
• bilateral - two sides. Symmetry between a single plane.
This leads to directionality.
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Classification by cephalization - the degree of brain development.
(The speed and direction at which an animal moves determines
degree and position of nerve development.) WHY?
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Copy Table 12.1 Summary of Majour Phyla into Notes
Phylum Porifera (Think: no tissues!)
organization
Sponges are considered the simplest of multicellular animals
because although they have specialized cells, the cells are not
organized into specialized tissues (remember the ‘hierarchy’)
feeding
figure 12.7, 12.8
reproduction
Sponges are hermaphroditic because they produce both egg and
sperm, but they do not self-fertilize because the gametes are
produced at different times. Zygote is free-swimming so it can travel
some distance before it settles down to start a new sponge. Because
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sponges are so simple, they can also reproduce by fragmentation
(when part breaks off).
ecology
Many sponges form symbiotic relationships with photosynthetic
bacteria and protists. Some even form associations with small
shrimp.
Phylum Cnidaria (Think tissues and radial symmetry!)
organization
Cnidarians have true tissues (with a middle layer of jelly-like matter
called mesoglea) and are radially symmetric. Most of their 10,000
species live in the oceans (marine) while only about 50 species are
freshwater dwellers. They have a primitive nerve net but no true
central nervous system (i.e. no cephalization). Have two body forms:
medusa and polyp. Some cnidarians live as medusoids (jellyfish)
while others live as polyps (hydra). Still others show alternation of
generations between the two forms (Obelia) (more on that later)
feeding
Use poisonous harpoons called nematocysts which are stored like
coiled springs inside specialised cells called cnidocytes (hence the
phylum name). When prey swim by, they inadvertently trigger a
“stinger missile” - ahh! Lunch! Food enters a blind digestive sac, the
contents digested and waste expelled through same opening. Can
eat larger prey than sponges. WHY?
reproduction
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medusoid forms - all produce sexually. Pseudo-gonads (false
reproductive organs) arise from epidermis, produce egg and sperm,
which is released into the water for fertilization, zygote settles and
starts again.
Polyp forms - generally produce asexually by budding under good
environmental conditions and sexually if conditions are not so great.
In this case the zygote will become a dormant cyst which will hatch
once conditions improve.
Obelia - Alternation of Generations
figure 12.11
specialization
In Obelia there is some degree of tissue specialization. Note some
polyps are reproductive, some are for feeding. This shows a division
of labour between tissues.
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ecology
There are many symbiotic relationships between fish, arthropods,
turtles and other small animals. Often the corals and jellyfish provide
protection while the other organisms provide a cleaning service.
Read p309 - 310 Ecology and Deep Sea Water Vents.
Phylum Platyhelminthes (Think: bilateral symmetry and a primitive
brain!)
What sets Planaria and other flatworms above the previous
organisms are the following
• true organs
• primitive organ systems
• some cephalization…two nerve cords ending in a concentration
of nerves
• eyespots
• ability to learn, co-ordination of movement. Negative phototaxic,
positive chemotaxic.
• blind digestive tract
• free-living and *parasitic forms
• rudimentary excretory system
• reproduction by sexual means (copulation) and asexual
(fragmentation)
Adaptations to a parasitic lifestyle.
• Limited size. Why?
To keep host from being ‘used’ to death.
• Lack of sensory structures. Why?
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• Lack of complex digestive structures. Why?
• Highly complex reproductive system. Why?
• Development of a protective, modified epidermis. Why?
• Sometimes a cuticle is present. Why?
Aschelminthes – Pseudocoelomates
A large taxa of worms which are considered ‘bridge’ organisms
between the lower acoelomates and higher coelomates. Common
characteristics include:
• a complete digestive tract…one way digestion! WHY IS THIS
IMPORTANT?
• a primitive brain and nerve cords running the length of the
animal
• no respiratory or circulatory system (transport is by diffusion).
They include a rather disgusting phylum of worms called nematodes
many of which are parasitic on almost every life form known …
Phylum Nematoda
Their ecological effects are far reaching and devastating as they
infest crops, domesticated cattle and humans.
Read p314-5
Life Cycle of Tapeworm
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Ascaris lumbricoles
A large mass of Ascaris lumbricoides that was passed from the intestinal tract.
The ruler at the bottom of the image is 4 cm (about 1.5 inches) in length.
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