Biodiversity of Animals explores the phylogeny of animals and the role of animals in agriculture and ecosystems. The notes are divided into two parts. Part 2 is called "Biodiversity of Animals Part 2".
Relationship between body plans of phyla and modes of liv
Role of invertebrates in the environment (select few invertebrates spoken ab
Summ
,Definitions
• Osculum: a mouth-like opening in sponges through which water and wastes exit
• Paralysed: cannot move
• Dorsoventrally: referring to the a view from the top to the bottom surface of an animal
• hydrostatic skeleton: a fluid-filled cavity under pressure
• appendages: parts of the body such as legs and antennae that are attached but move
separately
• notochord: a rod of cells along the dorsal side of a chordate's embryos
Role of some invertebrates in the environment
• Aerate: to introduce oxygen
• Gizzard: a specialised stomach made of strong muscle tissue to help with digestion
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,Relationship between
body plans of phyla
and modes of living
,The phylum Porifera (sponges)
• Sponges belong to the phylum Porifera, which
means pore bearing. There are over 10 000
species that belong to the phylum Porifera.
All are aquatic and mostly marine animals.
• Sponges range in size from less than a
centimetre to two metres. They can be
rounded, branching, cup-shaped, fan-shaped
or vase-shaped. They vary in colour and can
be red, yellow, blue, orange or purple.
• Larval sponges are free swimming, but adult
sponges are sessile. They are attached firmly
to sand, rocks or coral. The movement of
water through their bodies is suited to their
sessile mode of living.
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, Key features of Porifera
• Sponges are asymmetrical.
• Sponges have a vase-shaped body that surrounds an internal water-filled cavity. The body has an opening at the
top called the osculum and many holes or pores in the sides (hence the name Porifera) (see Figure 3.9).
o Water containing oxygen and food (mainly bacteria) is drawn into the body cavity through the pores, circulated
and then ejected through the osculum.
o Sponges do not have a nervous system or sense organs.
• Although sponges have cells with specialised functions they do not have tissues.
o The walls of the sponge consist of three functional layers surrounding the internal cavity.
o The inner laver consists of cells with flagella. The collar cells, or choanocytes, constantly beat their flagella to
circulate the water in the cavity bringing in a fresh supply of oxygen and food dissolved in the water. These cells
also capture and digest food particles in the water.
• The outer layer of the sponge is covered by flattened epithelial cells.
• Certain of the epithelial cells surround the pores of the sponge's body and can close them if necessary for
example, if there are poisonous chemicals in the water.
o Between the inner and outer layer of cells is a jelly-like substance which acts as a skeleton and may be
reinforced by fires or spines called spicules. It is this flexible skeleton of spicules which makes sponges useful
for washing and bathing.
o Within the jelly layer and positioned between the collar cells are cells called amoebocytes. These cells do the
actual digesting of food, but they can also move to where a cell is dying or has been lost to change or replace it.
They can become a tough epidermis cell or a collar cell when necessary.
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,The phylum Cnidaria (jellyfish, bluebottles, corals, sea anemones and hydras)
• There are more than 10 000 species in the phylum Cnidarian. They are all aquatic and live mostly in the
oceans. A hydra is a freshwater Cnidarian. Bluebottles and some other free-floating Cnidaria are
colonial. A bluebottle consists of a group of other individuals, which together looks asymmetrical
However, each individual is radially symmetrical. Coral reefs are built by tiny polyps that form colonies.
Each one secretes a substance that hardens into coral and protects it from carnivorous animals.
• Cnidarians have a simple body with tentacles and stinging cells.
• Cnidarians have two body forms, namely a polyp and medusa (see Figure The polyp form is attached to
a substrate, making it sessile. Hydras and sea anemones are polyp forms.
• The medusa form, for example a jellyfish, is free floating. They float around near the surface of the
water and usually move passively. However, some species called box jellyfish use their tentacles and
muscle cells to move through the water, and can even actively hunt their prey.
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,Key features of Cnidaria o Cnidarians have two kinds of body forms namely the se
the mobile medusa (see Figure 3.12). Both forms are ra
symmetrical. This is an advantage for a sessile organism
sense food or danger equally well from all sides.
o The body wall surrounds the gastrovascular cavity. The
food and circulating of nutrients, gases and removing o
place in the cavity. One opening, the mouth/anus contr
water into the cavity.
o Cnidarians have no blood system. Their thin-walled bod
dissolved oxygen to diffuse into their cells and dissolved
and other wastes to diffuse out of the cells into the gas
cavity.
o Cnidarians have cells that form tissues which are specia
different jobs.
o The dipoblastic body wall consists of an outer layer calle
ectoderm, consisting of protective epidermal cells. The
called the endoderm contains modified cells for digestio
secrete digestive juices. A jelly-like mesoglea is found b
layers. The mesoglea contains a network of nerves. The
nerves coordinates movements in response to stimuli.
o The mouth is surrounded by tentacles. The tentacles ha
that produce poison to paralyse prey.
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, The phylum Platyhelminthes (planaria, flukes such as the bilharzia worm and
tapeworm)
• The name Platyhelminthes comes from the Greek word platyhelminth, which means
• 'flat worms'. Their bodies are bilaterally symmetrical, soft, unsegmented and flat.
• They live either as free-living forms in ponds and streams or as parasites inside the
• bodies of their hosts. Examples of parasitic worms are Schistosoma, which causes
• bilharzia, and the tapeworm Taenia. Examples of non-parasitic flatworms are the
• turbellarian flatworms and Planaria (see Figure)
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, Key features of Platyhelminthes
o Platyhelminthes are dorsoventrally flat and thin. They are the simplest animals with bilateral symmetry as they have a c
defined rear end and the eye spots are positioned as mirror images on the left and right sides of the body. They are
sometimes brightly coloured.
o Flatworms have a specialised front end. Some show signs of a head-like region, including a pair of eyespots that are se
to light, a mouth under the body, and some nerve concentration. This simple collection of nerve cells is called a ganglio
Cephalisation is a feature that has allowed these animals to move.
• The body has a triploblastic body plan, but has no body cavity (coelom), as shown in Figure ( on next slide) The mesode
plays an integral part in the body plan of these animals. The mesoderm separates the ectoderm and the endoderm. It giv
to organs and systems such as true muscles and reproductive organs.
• Platyhelminthes have an incomplete gut with one opening, the mouth.
o Flatworms move along and seek prey. They eat small animals, either dead or alive. There is a branching gut with only o
entrance and no anus. The branched gut reaches close enough to all the body cells for the digested, dissolved food to
into body cells. Undigested food is egested from the mouth. Tapeworms are parasitic flatworms that live in the intestine
the host. They do not have a gastrovascular cavity and absorb digested food directly from the intestines of the host, thro
the body wall.
o Flatworms are acoelomates. This means there can be no independent movement of body wall muscles and gut muscle
Being an acoelomate limits the size to which the animal can grow. Tapeworms, however, can be very long.
o
No blood vessels have evolved from the mesoderm for the transport of food and oxygen for metabolism. This problem i
solved by the flat body shape which increases the surface area-to-volume ratio. This means that oxygen can easily diffu
directly from the environment into the body tissues and the cells instead of being transported by blood.
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