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ANIMAL CLASSIFICATION [Part 2]
TOPIC OUTLINE
A) Some general features of animalsB) Evolution of the animal body planC) CnidariaD) PlatyheminthesE) AnnelidaF) ArthropodaG) MolluscaH) Echinodermata I) Chordata
PHYLUM ARTHROPODA
Class: Insecta/ Hexapodabee
Class: Arachnida spiders
Subphylum: Crustacea water flea Daphnia, prawns, barnacles, crabs, lobsters, woodlice
Daphnia
Barnacles
Phylum Arthropoda contains more species than any other phylum
80%
~ 1 million arthropod species described
ubiquitous habitats [exist everywhere]
Phylum Arthropoda
The class insecta / hexapoda is the largest class.
1st major innovation in body structure among coelomates
Segmentation among annelids:
The development of jointed appendages : an even more profound
innovation
Jointed appendages mark the origin of the body plan
characteristic of the most successful of all animal groups.
include:
Jointed appendages :
legsantennae
mouthparts
are used for a variety of functions: feeding, locomotion and sensory purposes
the functional flexibility provided by such a broad array of appendages has made arthropods the most successful of animal groups
Arthropod bodies are segmented like those of annelids
the individual segments: often exist only during early development fuse into functional groups as adults
Head: 5-7 segments
Thorax: 3 segments
Abdomen: 11 segments
Specialisation of body parts: Tagmata
the arthropod body has undergone various forms of regional specialisation to produce segment groups specialised for different functions
these specialised body regions are called tagmata (singular, tagma) (e.g. the head, thorax and abdomen)
this fusing process is known as tagmatization, is of central importance in the evolution of arthropods
the head possesses sensory receptors: eyes antennae feeding appendages
the brain is much larger than in annelids
cephalisation is much more pronounced
Question: SEP 2013 Paper 2
Use your knowledge of biology to explain the evolutionary importance of the following:
tagmatisation in insects. (5)
Exoskeleton is secreted by the epidermis contains chitin, a nitrogen-containing
polysaccharide which resembles cellulose
Exoskeleton chitin has high tensile strength (it is difficult to break
by pulling from both ends)
the properties of the exoskeleton can be altered by the addition of other chemicals like in crustaceans, calcium salts makes it harder
a range of hardness, flexibility and stiffness is thus possible
flexibility is important at joints
Advantages of the exoskeleton:
1. support, particularly on land;2. it provides an anchor for the muscles internally;3. protection from physical damage;4. addition of a layer of wax from special glands in the epidermis
helps prevent desiccation on land;5. insect flight and the jumping ability of fleas and grasshoppers
depends on the presence of a remarkably elastic protein in the exoskeleton;
6. it has a low density, which is important for flying animals;7. flexible joints are possible between segments;8. it can be modified to form hard jaws for biting, piercing, sucking
or grinding;9. it can be transparent in places allowing, for example , entry of
light into eyes and camouflage in water.
TWO disadvantages associated with the exoskeleton:
Final body size is limited:
either not be able to support its own weight
or the exoskeleton would have to be so massive that it would not be able to move
An arthropod the size of an elephant would:
[The other important restriction on size of insects is their breathing mechanism which
works mainly by diffusion through tube called tracheae]
It restricts growth: so periodic moulting (ecdysis) is required if
the animal is to grow however, the arthropod is very vulnerable to
attack by predators at this period
The haemocoel
Coelom is a reduced in :
arthropods
Their main body cavity is the:
haemocoel
molluscs
develops from the cavities of the blood vascular system and is therefore filled with blood
the blood is generally circulated in the haemocoel, and through several attached blood vessels
the major organs are bathed in blood
The haemocoel
the coelom still exists but is: small confined to cavities of excretory organs and
the reproductive ducts
the high blood volume to body volume in arthropods enables them to maintain a high metabolic rate, allowing them to be very active animals
Flight in insects have greatly increases opportunities
for:finding food escaping predators
Cleidoic egg egg with a relatively impermeable shell is an adaptation to conserve water as it
prevents loss of moisture also found in birds and reptiles shell is porous to air shell may be flexible or calcerous it frees the animal from returning to water to
lay eggs
Question: MAY 2012 Paper 2
Use your knowledge of biology to explain the evolutionary importance of the following:
the cleidoic egg. (5)
Main features of the Arthropoda (Arthropods)
1. Triploblastic, coelomate.2. Metameric segmentation as in annelids but segments not
separated from each other by septa, definite in number, and showing varying degrees of specialisation.
3. Bilateral symmetry.4. Exoskeleton of chitin.5. Each segment typically bears a pair of jointed appendages
used for locomotion or feeding or sensory purposes.6. Coelom much reduced, main body cavity a haemocoel.7. Some groups have a compound eye for vision.8. Cuticle shed periodically (moulting or ecdysis) to allow for
growth.[diagnostic features: Exoskeleton; jointed appendages]
Main features of the class Insecta (Insects)
1. Mainly terrestrial.2. Well-defined head, thorax and abdomen.3. One pair of antennae.
Main features of the class Insecta (Insects)
4. Usually three pairs of mouthparts. 5. A pair of compound eyes and simple eyes.6. Three pairs of legs on thorax, one pair per
segment. Usually one or two pairs of wings on thorax.
7. Life cycle commonly involves metamorphosis either ‘complete’ or ‘incomplete’, with a larval stage.
8. No gills in adult. Gaseous exchange by tracheae
Subphylum: Crustacea
Spider crabCan weigh 19 kg.
1. Mainly aquatic.2. Cephalothorax (head and thorax not distinctly separate).
Main features of the subphylum Crustacea (Crustaceans)
A crustacean Carcinus maenas, the shore crab. Dorsal view.
Main features of the subphylum Crustacea (Crustaceans)
3. Two pairs of antennae.4. At least three pairs of mouthparts.5. A pair of compound eyes raised on stalks.6. Appendages often modified for swimming, as they
are mainly aquatic; number of legs variable, sometimes 10.
7. Larval form occurs.8. Typical gaseous exchange by gills – outgrowths of
the body wall or limbs.9. Dorsal side of body usually protected by a shield-like
carapace.
Main features of the class Arachnida (Arachnids)
1. Terrestrial.2. Cephalothorax; thorax separated from
abdomen by a narrow waist-like constriction (pedicel).
Spider
pedicel
3. No antennae.
Spider – dorsal view.
4. No true mouthparts but one pair of appendages used in capturing prey and one pair of sensory palps.
5. Simple eyes only (no compound eyes).6. Four pairs of walking legs.7. No larval forms.8. Gaseous exchange by book lungs or
tracheae.
Question: MAY 2007 Paper 2
“Arthropods are considered to be the most successful animals on Earth”. Discuss. (25)
Question: SEP 2002 Paper 2
Why are insects the most successful animals on Earth? Insects are successful animals as they have various adaptations to conserve water thus enabling them to inhabit a terrestrial environment. They excrete uric acid which does not require water for its elimination, from the Malpighian tubules. Their exoskeleton is covered by a thin layer of wax, making it waterproof. Their spiracles are guarded by valves, which close to reduce water loss from the tracheal system when the insect is at rest. Hairs at the spiracle have the same role. Embryos are enclosed in a relatively impermeable shell (cleidoic egg), allowing development outside the body without loss of water. They have diverse mouthparts allowing them to feed on solid or liquid food, thus reduce competing for food. Some possess wings which are an asset both to escape predators and to find a mate or new locations with bountiful resources.
Question: SEP 2005 Paper 2
Use your knowledge of biology to explain the following statement.
Scorpions and woodlice have very different appearances, yet are classified in the same phylum. (5)
TOPIC OUTLINE
A) Some general features of animalsB) Evolution of the animal body planC) CnidariaD) PlatyheminthesE) AnnelidaF) ArthropodaG) MolluscaH) Echinodermata I) Chordata
Slow-moving snails and slugs
Relatively sedentary bivalves such as clams
Highly active cephalopods (cuttlefish, squid, octopus)Types of
molluscs
PHYLUM MOLLUSCA Class: Gastropoda
slugs
snails
limpets
Mollusca: 2nd largest animal phylum
with almost 100 000 species
the giant squid is the largest non-vertebrate animal: weighs several
tonnes measures 16 m in
length
Molluscs were able to colonise :
aquatic & terrestrial environments by :
The more active molluscs show a
reduction or loss of the shell because:
2. The formation of a protective shell
1. The use of gills for gaseous exchange
A shell hinders locomotion.
Body plan of the Molluscabilateral symmetry
Visceral mass: is covered with a soft
epithelium contains the organs
of: digestion excretion reproduction
A muscular foot that is used in locomotion
Molluscs may have a differentiated head at the anterior end of the body: octopus
The muscular foot may be adapted for:
locomotion attachment food capture (in squids
& octopuses)
The mantle : is a thick epidermal sheet that covers the dorsal
side of the body bounds the mantle cavity
The mantle :
Secretes the calcium carbonate of the shell in those molluscs with a shell
The mantle cavity has a role in breathing:
Terrestrial molluscs:the mantle cavity forms a lung sac
Aquatic molluscs:the gills or ctenidia
project into the mantle cavity
Ctenidiaconsist of filaments rich in blood vessels:
greatly increase the surface area capacity for gas exchange
mollusc gills are very efficient
can extract 50% or more of the dissolved oxygen from the water that passes through the mantle cavity
this water: brings in oxygen
and, in the case of the bivalves, food;
carries waste materials and gametes
in aquatic molluscs, a continuous stream of water passes into and out of the mantle cavity, drawn in by the cilia on the gills
Locomotion some molluscs e.g. slugs secrete
mucus, forming a path that they glide along on their foot
in cephalopods (squids and octopuses) the foot is divided into arms, also called tentacles
in some pelagic forms (molluscs that are perpetually free-swimming), the foot is modified into wing-like projections or thin fins
Feeding
the radula: a rasping, tongue-like
organ used for feeding
one of the most characteristic features of all the molluscs except the bivalves
radula
food
Scraps of food
dozens of microscopic, chitinous teeth arranged in rows
The radula consists primarily of :
gastropods use their radula to:
Scrape algae & other food
materials off their substrates
… then to convey this food
to the gut
Circulationthe circulatory system of all molluscs except
cephalopods consists of: a heart an open
circulation
Cephalopods:a closed circulatory
system aids their active form of life
The coelomis primarily represented by a small cavity
around the heart
Coelom
Main features of the Mollusca1. Bilaterally symmetrical.2. Unsegmented, triploblastic coelomates.3. Body soft and fleshy and divided into a head,
ventral muscular foot and dorsal visceral hump.4. The mantle secretes a calcereous shell.5. Main body cavity is the haemocoel.6. No limbs.7. Gaseous exchange effected by one or more pair/s
of ctenedial gills housed in the mantle cavity.[Diagnostic feature: Body soft and fleshy and divided into a head, ventral muscular foot and dorsal visceral
hump.]
Main features of the class Gastropoda
1. Terrestrial, marine and freshwater.2. Asymmetrical.3. Shell of one piece, usually coiled due to
rotation of hump during growth.
Main features of the class Gastropoda
4. Large flat foot used in locomotion.5. Head, eyes and sensory tentacles.6. Radula, a rasping tongue-like structure used
in feeding.7. Anus at anterior.
Operculum : a plate present in most marine
gastropods that the animal can pull to close the shell
most adult land gastropods
most gastropods have a pair of tentacles with eyes
these tentacles have
been lost in some of the more advanced forms of the class
EYE
TOPIC OUTLINE
A) Some general features of animalsB) Evolution of the animal body planC) CnidariaD) PlatyheminthesE) AnnelidaF) ArthropodaG) MolluscaH) Echinodermata I) Chordata
Phylum: Echinodermata
deuterostomate, triploblastic animals
have no proper circulatory system
Class: Asteroidea (starfish e.g. Asterias)
Class: Echinoidea (sea urchins e.g. Echinocardium
all marine are largely bottom-dwellers (benthic) inhabiting
shorelines and shallow seas
Echinoderm body plan undergoes a fundamental shift during development
all echinoderms have secondary radial symmetry: larvae are bilaterally symmetrical but adults
become radially symmetrical
Question: SEP 2012 paper 2
Use your knowledge of biology to explain the following statements
echinoderms exhibit secondary radial symmetry. (5)
show pentamerous symmetry (a form of radial symmetry)
Adult echinoderms have a five-part body plan
Endoskeleton ‘echinoderm’ means spiny skin
refers to an endoskeleton composed of hard calcium-rich plates just beneath the delicate skin
in adults, the plates frequently fuse, forming a hard shell
The plates in certain portions of the body of some echinoderms are perforated: tube feet, part of the water
vascular system [a unique feature of this phylum] extend
TS arm of starfish
Tube feet
Ossicles in the skin provide sessile animals with:support protection from predators + wave action
Ossicles in starfish
The water vascular system
is a hydraulic system which aids in:MovementRespirationExcretionFeeding
the water vascular system radiates from a ring canal that encircles the oesophagus
Five radial canals extend into each of the five parts
of the body and determine the basic
symmetry
Madreporite: a sieve-like plate on the animal’s surface location through which water enters the water vascular system
and flows to the ring canal through a tube, or stone canal
The five radial canals in turn extend out through short side branches into the hollow tube feet
Suckers may be present at the end of each tube
foot
Modified tube feet around the mouth cavity of certain echinoderms
are used in feeding
Body cavity the coelom:
is connected with a complicated system of tubes
helps provide circulation & respiration
the digestive system is simple but usually complete, consisting of :
gut
mouth
anus
coelom
Reproductionmany echinoderms are able to regenerate
the lost part
some echinoderms, especially starfish, drop various parts when under attack
Reproductionin a few echinoderms, asexual reproduction
takes place by splitting [Fragmentation] the broken parts of sea stars can
sometimes regenerate whole animals
Reproduction
most reproduction in the phylum is:
sexual external
sexes are separate
[free-swimming – form part of plankton]
Metamorphose into sedentary adults
Male Female
Fertilised egg
Bilaterally symmetrical larva
Main features of Echinoderms1. Triploblastic, coelomate.2. Skin contains calcareous ossicles (endoskeleton)
and spines.3. Exclusively marine.4. Adult with five-rayed symmetry, but larva is
bilaterally symmetrical.5. Mouth generally on lower (oral) side; anus on
upper (aboral) side.6. A coelomic water vascular system which contains
and is in direct contact with sea water and which operates hydraulically the locomotory tube feet (podia).
7. No proper circulatory system.8. No differentiated head.9. No excretory organs.10. A through gut.11. Sexes are separate.12. Nervous system diffuse, decentralised,
allowing them to engage in their environment equally from all sides.
[Diagnostic features: pentamerous radial symmetry; tube feet]
Characteristics of the Class Asteroidea (starfish)
characterised by a flattened body which grades into 5 or sometimes more (up to 40) arms
the animals are not attached and freely mobile
few calcareous plates in body wall; movable spines
Characteristics of the Class Asteroidea (starfish)Pedicellariae: modified spines which act as scissors or
forceps to remove organisms that try to settle down on their body surface
Characteristics of the Class Asteroidea (starfish)starfish are mostly
carnivorous
digestion is mostly extracellular
anus has little function
Main features of the Class Echinoidea (sea urchin)
spherical, free-living echinoderms which lack arms
numerous calcareous plates in the body wall, attached to each other to form a rigid test
the test bears:pedicellariae movable spines
Main features of the Class Echinoidea (sea urchin)
the mouth bears a distinctive grazing apparatus, called Aristotle’s lantern used for chewing
Teeth of Aristotle’s lantern
Question: SEP 2005 Paper 2
Use your knowledge of biology to explain the following statement.
Starfish and sea-urchins have very different appearances, yet are classified in the same phylum. (5)
TOPIC OUTLINE
A) Some general features of animalsB) Evolution of the animal body planC) CnidariaD) PlatyheminthesE) AnnelidaF) ArthropodaG) MolluscaH) Echinodermata I) Chordata
Phylum: CHORDATA [Chordates]
Sub phylum: VertebrataClass: Osteichthyes / Teleosta (bony fish -
teleosts) Class: Amphibia (amphibians: newts,
salamanders, frogs and toads) Class: Reptilia (reptiles) Class: Aves (birds) Class: Mammalia (only this class in syllabus)
Four principal features characterise chordates:• Notochord • Dorsal hollow nerve cord
• Pharyngeal slits• Muscular, postanal tail.
runs just beneath the dorsal surface of the animal
hollow means it is filled with fluid in vertebrates, the dorsal nerve cord
differentiates into the:
1. A single, hollow nerve cord
brain spinal cord
2. A flexible rod, the notochord
is present at some stage in the life cycle in all chordates
forms on the dorsal side of the primitive gut in the early embryo
during embryological development in most vertebrates by the vertebral column that runs around the nerve cord.
The notochord becomes surrounded and then replaced
connect the pharynx, a muscular tube that links the mouth cavity and the gullet, with the outside
in most vertebrates, the slits do not actually connect to the outside and are better termed pharyngeal pouches
3. Pharyngeal slits
pharyngeal pouches are: present in the embryos of all vertebrates but are lost later in the development of terrestrial
vertebrates
the presence of these structures in all vertebrate embryos provides a clue to the aquatic ancestry of the group.
extends beyond the anus, at least during their embryonic development
nearly all other animals have a terminal anus
4. The postanal tail
All chordates have all four of these characteristics at some stage in their lives e.g.
Human adults retain only the: nerve cord one pair of pharyngeal
slits which are the Eustachian tubes that connect the throat to the middle ear
Human embryoshave all four features
In addition to these four principal features, a number of other
characteristics distinguish the chordates fundamentally from other
animals: chordates have a more or less segmented body plan,
and distinct blocks of muscles can often be clearly seen in embryos of this phylum
most chordates have an internal skeleton against which the muscles work
either this internal skeleton or the notochord makes possible the extraordinary powers of locomotion that characterise the members of the group
Main features of Chordates1. Notochord present at some stage in the life history. 2. Post-anal tail (tail starts posterior to anus).3. Bilateral symmetry.4. Pharyngeal (visceral) clefts present (slits in the
pharynx).5. Dorsal, hollow nerve cord.6. Triploblastic coelomate.7. Segmental muscle blocks (myotomes) on either side
of the body.8. Limbs formed from more than one body segment.
[diagnostic features : 1-4]
Main features of the subphylum Vertebrata
1. Notochord replaced in adult by a vertebral column (backbone), a series of vertebrae made either of bone or cartilage.
2. Well-developed central nervous system including brain. Skull protects the brain. A high degree of cephalisation.
3. A living endoskeleton.4. Pharyngeal clefts (gill slits) few in number.5. Two pairs of fins or limbs. These are attached to the
rest of the skeleton by girdles, pectoral and pelvic.6. Closed circulatory system.
Reptiles, birds and mammals:the amniotes
possess extraembryonic membranes, including an amnion, during development
Wastes are discharged into another sac called
the allantois.
The embryo obtains food from a yolk sac attached to its gut.
Within the shell are several extraembryonic membranes that protect the embryo from drying and assist gas exchange and excretion of nitrogen.
The pentadactyl limb has five digits on the hand & foot has a specific pattern of bones
Penta = 5 Dactyl = Fingers
The structure of a human arm includes
A bone between the shoulder and the elbow: humerus.
Below the elbow, are two other bones: radius ulna
A set of wrist bones and then the five-digit fingers,
follow.
1
23
The pentadactyl limb is found in all classes of tetrapods
The fundamental structures of pentadactyl limbs are the same in all tetrapods indicating that they
originated from a common ancestor.
But in the course of evolution these fundamental structures have been
modified they have become:
superficially different unrelated structures
this phenomenon is shown in the forelimbs of mammals
to serve different functions in
adaptation to different environments & modes of
life
The pentadactyl limb is a homologous structure
Homologous structures have the same basic plan but are adapted for different functions
Basic pentadactyl
pattern
WalkingRunningFlying
Swimming
Question: MAY 2003
Write brief notes on the evolutionary significance of each of the following structures: [five marks]The pentadactyl limbTypical limb of the mammals, birds, reptiles, and amphibians. The limb has three parts a hand/foot with five digits (fingers/toes), a lower limb containing two bones, and an upper limb containing one bone. This basic pattern has persisted in all the terrestrial vertebrates, and those aquatic vertebrates (such as seals) which are descended from them. Natural selection has modified the pattern to fit different ways of life. In flying animals (birds and bats) it is greatly altered and in some vertebrates, such as whales and snakes, the limbs are greatly reduced or lost. Pentadactyl limbs of different species are an example of homologous organs.
Main features of Mammalia
1. Skin bears hair with two types of glands, sebaceous and sweat.2. Bony skeleton.3. Two pairs of pentadactyl limbs.4. Visceral clefts never develop gills.5. External ear.6. Only two genera lay eggs, the spiny anteater and the duck-billed platypus.7. Embryo develops in mother. Young born in a more mature state, i.e.
mammals are viviparous.8. Mother has mammary glands which produce milk for the newborn.
Internal fertilisation.9. Muscular diaphragm.10. Well-developed sense organs.11. A highly developed brain and intelligent behaviour involving learning and
memory.12. Heterodont dentition (various types and sizes of teeth)13. A bony roof to the mouth called the palate.14. Endothermic.
Question: MAY 2008 Paper 2
Use your knowledge of biology to describe the selective advantage of each of the following adaptations:
viviparity (live birth) in mammals. (5)
Evolutionary trends shown in vertebrates towards adaptation to
a terrestrial mode of life
Creatures that make the transition from life in water to life on land, must come to terms with FOUR new exigencies: they must
1. find ways to cope with gravity;2. breathe air;3. avoid desiccation;4. evolve senses that are appropriate to air
rather than water