ANIMAL CLASSIFICATION [part 1]

Syllabus requirements

1.2Classification

1.2.1 The meaning ofand evolutionarysignificance of thefollowing terms:

i) prokaryotic and eukaryotic cellsii) endosymbiotic origin of plastids and

mitochondriaiii) radial and bilateral symmetryiv) diploblastic and triploblastic

organisationv) acoelomate and coelomate body plansvi) metameric segmentationvii) jointed appendagesviii) the pentadactyl tetrapod limbix) transition of gills to lungsx) cleidoic egg

TOPIC OUTLINE

A) Some general features of animalsB) Evolution of the animal body planC) CnidariaD) PlatyheminthesE) AnnelidaF) ArthropodaG) MolluscaH) Echinodermata I) Chordata

Animals are so diverse that few criteria fit them all

Some features e.g. being consumers, apply to all

Barnacles are sessile (cannot move from place to place).

others, e.g. being mobile, have exceptions

Considering all characteristics, there is enough evidence to show that animals have descended from a common ancestor

Nine General features of animals:

1. Heterotrophy all animals obtain energy and organic

molecules by ingesting other organisms

2. Multicellularity all animals are multicellular

3. No cell walls: animal cells are usually quite flexible the many cells of animal bodies are held together by

extracellular frames of structural proteins e.g. collagen

Collagen fibre

4. Active movement: animals move:

more rapidly in more complex ways

this ability is perhaps their most striking characteristic, one directly related to the:

than members of other kingdoms

1. flexibility of their cells 2. evolution of nerve &

muscle tissues

Many animals are:

Flying is unique to animals

sessile:cannot move from

place to place

sedentary: move rarely or slowly, although they have muscles

5. Diversity in form: animals vary greatly in form: ranging in size

from

almost all animals lack a backbone

enormous whales and giant squids

microscopic

6. Diversity in habitat: 35-40 phyla in the animal kingdom

Most have members that occupy only the sea e.g. Echinodermata

Members of fewer phyla occur in freshwater

Members of: Arthropoda Mollusca Chordata

successful in the sea also dominate

animal life on land

7. Sexual reproduction: most animals reproduce sexually.

Ovum Sperm

Ovum Sperm

Hermaphrodites

8. Embryonic development: an animal zygote first undergoes a series of

mitotic divisions: cleavage

Cleavage produces a hollow ball of cells:

blastula

In most animals the blastula folds inward at one point to form a hollow sac with an opening at one end called the blastopore. An embryo at this stage is called a gastrula.

The subsequent:growth development

Larva: looks differently from adult lives in a different habitat eats different sorts of food in most groups it is very small undergoes metamorphosis

differs between groups of animals

Embryos of most kinds of animals develop into

a larva

9. Tissues: the cells of all animals except sponges are organised

into structural and functional units called tissues

Tissue:collections of cells that together

are specialised to perform specific tasks

Animals are unique in having two tissues associated with movement:

1) muscle tissue2) nervous tissue

TOPIC OUTLINE

A) Some general features of animalsB) Evolution of the animal body planC) CnidariaD) PlatyheminthesE) AnnelidaF) ArthropodaG) MolluscaH) Echinodermata I) Chordata

BODY PLAN is the:

general structure, arrangement of organ systems,

and integrated functioning of parts

The features described in the previous section evolved over millions of years

People can understand how the history of life has proceeded by examining the types of :

present in fossils and in existence today

animal bodies & body plans

Five key innovations can be noted in animal evolution:

The evolution of:1. symmetry.2. tissues, allowing specialised structures and

functions.3. a body cavity.4. various patterns of embryonic development.5. segmentation, or repeated body units.

1. THE EVOLUTION OF SYMMETRY

Symmetrical Asymmetrical

e.g. snails

Member of the phylum Cnidaria (jellyfish, sea anemones, and corals) exhibit radial symmetry

Symmetrical bodies first evolved in marine animals

Jellyfish

An animal is symmetrical if it can be divided into similar halves on at least one plane

If not—asymmetric—many spongesAsymmetrical animals lack complex sensory and

locomotory functions

Bilateral symmetry[beetle]

Radial symmetry[coral]

No symmetry[sponge]

RADIAL SYMMETRY is a body design

in which the parts of the body are arranged around a central axis in such a way that any

plane passing through the central axis divides the organism into halves that are

approximate mirror images

In general, radial symmetry leads to:

a sessile passively floating existence

OR

Sessile animals: stay in one place must move the environment and food to themselves

BILATERAL SYMMETRY is a body design

the plane runs from the: anterior end (head) to posterior end (tail)

Dorsal

Ventral

Anterior

Posterior

in which the body can be divided into similar halves on only one plane

BILATERAL SYMMETRY allows parts of the body to evolve in different ways

Anterior side gives rise to the

head

Bilateral symmetry is correlated with:1. Cephalisation2. An active way of life3. Moving in one direction

Posterior sidegives rise to the

tail

Cephalisation:concentration of sensory organs and nerve

tissues at the anterior end or headthe anterior end:

encounters the environment first has structures to:

capture prey avoid predators

now organisms can sense and move in one definite direction

Bilaterally symmetrical animals move from place to place more efficiently than radially symmetrical

ones. Significance of this is:

They are efficient in: seeking food, shelter and mates avoiding predators

Question: SEP 2012 Paper 2

Use your knowledge of biology to explain the evolutionary importance of the following:radial symmetry in sessile animals. (5)

Question: SEP 2013 Paper 2

Distinguish between the following terms, including an example of an organism for each term.bilateral symmetry and radial symmetry. (5)

What is an animal?

[use information in syllabus for definition]

An organism: without cell walls, is heterotrophic, is generally motile shows cephalisation, develops from a blastula in early

development.

True tissues

Radial symmetry Bilateral symmetry

Protostomes

No true tissues

Deuterostomes

Bilateria vs Radiata

Bilateria:all the animals showing bilateral symmetry

Radiata:are those showing radial symmetry

are an exception

Adults: near-radial symmetry

Larvae: bilaterally symmetrical

The Radiata:develop from two embryonic tissue layers -

germ layers inner endodermouter ectoderm

are diploblastic

The Bilateria: are triploblastic have three tissue layersmesoderm forms:muscles most organs located between the digestive

tract & the outer covering of the animal

also stem from the mesoderm

vertebrate circulatory skeletal systems

True tissues

RADIATA BILATERIA

Protostomes Deuterostomes

No true tissues

The Bilateria: a step up in multicellular complexity from Radiata

Question: MAY, 2008

1. Echinoderms, such as starfish and sea-urchins, are radially symmetrical yet are classified within the Bilateria. Suggest an explanation for this. (2)

Since larvae are bilaterally symmetrical and the adults are secondarily radially symmetrical.

Question: MAY, 2008

2. Suggest ONE reason that may explain why the Bilateria and Radiata are not usually included as natural groupings in formal classification schemes. (2) As they contain many phyla with many different characteristics. Some larvae of cnidaria are bilaterally symmetrical.

Question: SEP 2007 Paper 2

Use your knowledge of biology to explain the following:

Cnidarians and Echinoderms are both characterised by radial symmetry yet are not considered to be closely related. (5)

Five key innovations can be noted in animal evolution:

The evolution of:1. symmetry.2. tissues, allowing specialised structures and

functions.3. a body cavity.4. various patterns of embryonic development.5. segmentation, or repeated body units.

2. THE EVOLUTION OF TISSUES the zygote has the capability to give rise to all the

kinds of cells in an animal’s body: it is totipotent (all powerful)

Unipotent:having the ability to self-renew but differentiate into only one type of cell or tissue.

Examples

Circulatory system Nervous system

Immune system

Pluripotent:the cell having the ability to differentiate into more than one cell type.

2. THE EVOLUTION OF TISSUES

during embryonic development, cells specialise to carry out particular functions

in all animals, except sponges, the process is irreversible: once a cell differentiates to serve a function, it and its descendants can never serve any other function

cells of animals, other than sponges, are organised into tissues, each of which is characterised by cells of particular morphology and capability

Five key innovations can be noted in animal evolution:

The evolution of:1. symmetry.2. tissues, allowing specialised structures and

functions.3. a body cavity.4. various patterns of embryonic development.5. segmentation, or repeated body units.

3. THE EVOLUTION OF A BODY CAVITY

is another key transition in the evolution of the animal body plan

the evolution of efficient organ systems within the animal body depended critically upon a body cavity for:supporting organsdistributing materials fostering complex developmental

interactions

.the bodies of all other animals are marked by

a fundamental bilateral symmetry,

Three basic kinds of body plans in the bilateria

Tube within a tube body plan

Acoelomates Pseudocoelomates

Coelomates

have no body cavity:

Acoelomates: (Platyhelminthes)

have a body cavity called pseudocoel located between the mesoderm and endoderm

Pseudocoelomates: (Nematodes)

have a fluid-filled body cavity that develops entirely within the mesoderm

(Annelids, Arthropods, Molluscs, Echinoderms & Chordates)

Coelomates:

The coelom is:the main body cavity of many triploblastic

animalsan extensive internal space or body cavity

which separates the body wall from the gut

The coelomis lined entirely by mesodermcontains coelomic fluid

Question: SEP 2012 Paper 2

Distinguish between the following terms, including an example of an organism for each term.coelomate and acoelomate. (5)

Coelom is a reduced in :

arthropods

Their main body cavity is the:

haemocoel

molluscs

The haemocoelcontains blood unlike the coelom, it never:

contains gametes communicates with the exterior

The development of the coelom poses a problem:

Solution: development of a circulatory system

Five key innovations can be noted in animal evolution:

The evolution of:1. symmetry.2. tissues, allowing specialised structures and

functions.3. a body cavity.4. various patterns of embryonic development.5. segmentation, or repeated body units.

4. THE EVOLUTION OF VARIOUS PATTERNS OF EMBRYONIC DEVELOPMENT

coelomate animals are divided into:

differ in the way in which the embryo grows

Let us see how they differ….

protostomes deuterostomes

The Bilateria develop from a blastula

Early in embryonic growth, when the embryo is a blastula, a portion invaginates inwards

to form an opening: blastopore

Fate of the blastopore differs.

Blastopore – opening to the primitive digestive tract

Five key innovations can be noted in animal evolution:

The evolution of:1. symmetry.2. tissues, allowing specialised structures and

functions.3. a body cavity.4. various patterns of embryonic development.5. segmentation, or repeated body units.

5. THE EVOLUTION OF SEGMENTATION

segments are able to function independentlyfirst appeared in annelidssegmentation underlies the organisation of

all advanced animals

Segmentation: is the repetition of identical body units

TWO advantages to early embryonic segmentation:

1. Repetition of organ systems is less lethal if one segment is damaged

2. Locomotion is easier when segments can move independently

Advantages to early embryonic segmentation:

Offers evolutionary flexibility - small change in a segment can produce a segment with new function

Segments can be modified for various activities: reproduction, feeding, excretion

the segments are fused, but segmentation is usually apparent in their embryological development

In some adult arthropods :

Fused segments of cephalothorax

not apparent in human adults: visible in embryo

vertebrate muscles develop from repeated blocks called somites

vertebral column segmentation is more apparent

Segmentation:

TOPIC OUTLINE

A) Some general features of animalsB) Evolution of the animal body planC) CnidariaD) PlatyheminthesE) AnnelidaF) ArthropodaG) MolluscaH) Echinodermata I) Chordata

PHYLUM CNIDARIA

Cnidarians: nearly all marine, a few live in freshwater

about 11,000 species

Class: Hydrozoa Class: Scyphozoa (jelly fish e.g. Aurelia)

Obelia Hydra

radially symmetrical

a sac body plan: one opening – no anus

blind-ending gastrovascular cavity / enteron /gut functions in: digestion circulation gas exchange by diffusion as a hydrostatic skeleton

Cnidarians

Sac body plan

Mouth / anus

Constraints imposed by blind -sac body plans

1. Size2. Limited locomotion3. No separation of consumption and excretion4. Restricted to aquatic or marine

environment, or as an internal parasite of terrestrial animals

diploblastictissue level of organisation

Cnidarians

Epidermis forms from Ectoderm

Gastrodermis forms from Endoderm

Mesoglea: is the translucent, non-living, jelly-like substance found between the two cell layers

tentacles encircle the mouth at one end of the body

are carnivorous - catch their prey (e.g. fishes, crustaceans) with the tentacles

Cnidarians :

Hydra feeding on a water flea (Daphnia).

Tentacles around outer margin of the bell in a jellyfish.

The phylum is called the Cnidaria

due to presence of 'thread organelles‘ called cnidae [singluar: cnida]

Thread organelle is located inside a

thread cell called cnidocyte

LEARN:Structure Description Cnidocil a hairlike sensory process projecting from the

surface of a cnidoblast, believed to trigger the discharge of the nematocyst

Cnidoblast the developing 'thread cell'

Cnidocyte ‘thread cell’ - is an explosive cell containing one giant thread organelle or cnida

Nematocyst a capsule containing a barbed, threadlike process found in certain cells on the externalsurface of cnidarians

The phylum is called the Cnidaria

cnidocil

cnidocyte

Nematocystcnida

Nematocyst: a small but powerful ‘harpoon’, unique to the phylum is pushed outward so explosively that it can penetrate

even the hard shell of a crab

Cnidocytes contain everting structures called nematocysts

Nerves are arranged in nets

Reproduction is:Asexual

e.g. by budding in HydraOr medusae production in

Obelia

Sexual often involves a ciliated larva e.g. in Obelia

Question: MAY 2014, Paper 2

Use your knowledge of biology to explain the following:

Cnidocytes are characteristic of Cnidaria. (5)

Two basic body types occur in the cnidarians:

Polyp cylindricalsessile

Medusa umbrella-shapedfree-swimming or floating

Sessile: remains attached to a surface throughout its life and shows little or no locomotion

Polyp / hydroid phase

Medusa

[Manubrium - a stalk-like structure bearing the mouth at its tip.]

The two types sometimes alternate in the life cycle

acts as a dispersal stage reproduces sexually

reproduces asexually by budding off medusae

MEDUSA

POLYP

Polymorphism: the situation in which individuals of a species exist in two or more different

forms

Individual polyps within colonies can vary in form :

they may be specialised for:

Obelia

asexual reproduction

feeding

Class: Hydrozoa [hydroids] Polyp dominant life cycle Medusa simple Polyps solitary or colonial

Part of a colony of Obelia.

Class: Scyphozoa [jellyfish] Small polyp sometimes present as a larval stage. Large highly organised medusa dominant in life cycle.

Aurelia – oral view.

All canals are part of the gastrovascular

cavity.

Animals from this point onwards generally show the following

characteristics:

TRIPLOBLASTIC BILATERAL SYMMETRY ANTERIOR END (head),

POSTERIOR END (tail), DORSAL SIDE (back) VENTRAL SIDE (front)

PlatyheminthesAnnelidaArthropodaMolluscaEchinodermataChordata

TOPIC OUTLINE

A) Some general features of animalsB) Evolution of the animal body planC) CnidariaD) PlatyheminthesE) AnnelidaF) ArthropodaG) MolluscaH) Echinodermata I) Chordata

PHYLUM PLATYHEMINTHES (flatworms)

can live nearly anywhere- on land, in fresh or marine water

Class: Turbellaria (Planaria)

Class: Cestoda (Taenia)

PLATYHEMINTHES

triploblastic - originating from three tissue layers:

acoelomate - as there is no body cavity or coelom in the mesoderm

organ level of development

PLATYHEMINTHEShave no blood system

As in cnidarians, there is a

single gut opening.

Planaria

An extensively branched gut is usually present e.g. Planaria

belongs to the order :Tricladida having an intestine with:

one anterior two posterior branches

Planaria is a triclad

the gut delivers food to all parts of the body

mouth

There is a distinct head, often with:

Class: TurbellariaGenus: Planaria

sense organsa primitive internal brainthe development of complex structures in

the head is called cephalisation

Class: TurbellariaGenus: Planaria

Protonephridiaare excretory / osmoregulatory structures

Regeneration in a Planarian

Main features of the class Turbellaria (turbellarians)

1. Free living, aquatic2. Outer surface covered with cilia for

locomotion; cuticle3. Delicate, soft body4. Suckers rarely present5. Enteron present6. Sense organs in adult

The outer surface of a typical turbellarian

Main features of the class CestodaEndoparasitic (live inside host).

Taenia

Elongated body divided into proglottids which are able to break off.

Main features of the class Cestoda

Suckers and hooks on ‘head’ (scolex) for attachment to host.

Hooks

Taenia

Suckers

Strobilation : in the tapeworm:

is the process of transverse fission which produces proglottids from behind the scolex

strobilus (plural: strobili) is a ribbon-like chain of proglottids

Main features of the class Cestoda

1. Thick cuticle (protection); no cilia in adult.2. No enteron (no digestion required –

absorbs pre-digested food from host).3. Sense organs only in free-living larval

stages.

Question: SEP 2013 Paper 2

Use your knowledge of biology to explain the evolutionary importance of the following:

triploblastic organisation in animals. (5)

TOPIC OUTLINE

A) Some general features of animalsB) Evolution of the animal body planC) CnidariaD) PlatyheminthesE) AnnelidaF) ArthropodaG) MolluscaH) Echinodermata I) Chordata

Animals from this point onwards generally show the following

characteristics:

COELOM METAMERIC SEGMENTATIONCIRCULATORY SYSTEM

AnnelidaArthropodaMolluscaEchinodermataChordata

PHYLUM ANNELIDA (annelids or segmented worms)

live in the sea, most freshwater habitats, and damp soil

Class: Polychaeta(bristleworms e.g. Nereis - ragworm)

Class: Oligochaeta (earthworms e.g. Lumbricus)

Diagnostic feature of annelids:Chaetae / setae

- stiff bristles of chitin secreted by the epidermis

Class: Polychaeta[poly = many

chaetae]

Class: Oligochaeta[oligo = few]

TS Lumbricus

Chaetae

Nereis

A variety of annelids

Leeches: NOT in syllabus]

Metameric segmentation:the building of a body from a series of similar segments

arose in the annelids

Advantage of segmentation:1. offers evolutionary flexibility – a small

change in an existing segment can produce a new segment with a different function

2. segments can be modified for reproduction, feeding, or eliminating wastes

Question: MAY 2009 Paper 2

Use your knowledge of biology to describe the selective advantage of each of the following adaptations:–Metameric segmentation; (5)–Triploblastic body plans. (5)

Annelids are characterised by 3 principal features:

1. Repeated segments2. Specialised segments3. Connections

1. Repeated segments the body segments:

Internally are divided from one another by partitions called septa

Externally are visible as a series of ring-like structures

running the length of the body

Each segment has a: pair of excretory organs

(nephridia) nerve centre (ganglion)

SEPTUM

The fluid-filled coelom of each

segment creates a hydrostatic skeleton (liquid-supported)

that gives the segment rigidity. TS earthworm

coelom

Muscles within each segment push against

the fluid in the coelom.

because each segment is separate, each can: expand contract

this lets the worm move in complex ways

Locomotion in earthworm. Note retracted chaetae in segments are

elongated.

Annelids move by a hydrostatic skeleton

Swimming in Nereis

independently

2. Specialised segments at the anterior end of annelids

have become modified to contain specialised sensory organs - some are sensitive to light

elaborate eyes with lenses & retinas have evolved in some annelids

A well-developed cerebral ganglion / brain is contained in one anterior

segment

Dorsal view of Nereis

EYE

3. Connectionsalthough partitions separate the segments,

materials (in blood) information (impulses)

do pass between segments

Annelids have a closed circulatory system that carries blood from one segment to another

Ventral nerve cords connect the: ganglia in each segment with one another

AND the brain

So the brain can coordinate the worm’s activities

cerebral ganglion / brain

ganglion in segment

Body plan: a tube within a tube

a tube - the gut within a tube - the muscular, slimy, moist

outer body

Advantages of Tube within a Tube

Body Plans

Separation of feeding and excretory pores

Specialization of tissues for different functions

Development of true muscle tissue permitting greater movement

In most annelids, each segment typically possesses chaetae or setae

bristles of chitin that help anchor the worms during

locomotion or in their burrows

Chaetae (singular: chaeta):

TS earthwormA crawling worm:

retracts the chaetae in the expanding segments

extends the chaetae in the contracted segments to make contact with the surface

Gaseous exchange in annelids

However, much of their oxygen supply reaches the different parts of their bodies

through their blood vessels.

Some of the blood vessels in annelids

are enlarged heavily muscular 5 pulsating blood vessels on each side of an

earthworm that serve as hearts: helping to pump blood:

serving as hearts that pump the blood

From the main dorsal vessel

To the main ventral vessel

Main features of Annelida

1. Triploblastic, coelomate.

2. Bilateral symmetry.

3. Metameric segmentation.

Nereis

4. Prostomium, a lip-like extension of the first segment situated above the mouth.

5. A closed blood system.6. A varying degree of cephalisation.

7 . Definite cuticle (outer covering)

8. Chaetae, hair-like structures made of chitin

TS earthworm

Class Polychaeta: Nereis

lives in estuaries under stones, or in mud or muddy sand burrows

all segments, apart from those most anterior and posterior, are very similar to each other

on either side of each segment is a projection called the parapodium

Two functions of parapodia:

Act as a:1. paddle2. a gill

A paradodium

A distinctive head indicates cephalisation

The head consists of:

A posterior peristomium (the second segment)

The head consists of:

An anterior prostomium (the first segment)

A posterior peristomium (the second segment)

On the prostomium there are:

A pair of sensory tentacles (sensitive to touch)

Two pairs of eyes

A pair of fleshy palps (sensitive to touch)

Dorsal view of Nereis head.

On the peristomium: 4 pairs of long, flexible hairs or cirri

1. sensitive to touch 2. have chemoreceptors giving the animal the

equivalent sense of taste and smell

Peristomial cirri

Main features of the class Polychaeta (The Polychaetes)

1. Marine.2. Distinct head.3. Chaetae numerous on lateral extensions of

the body called parapodia. 4. No clitellum.

[diagnostic feature: parapodia]

Class Oligochaeta e.g. Lumbricus [earthworm]

Despite being a terrestrial animal, it has not fully overcome all the problems associated with life on land.

To prevent desiccation: it lives underground in

burrows in damp soil emerges only at night

to feed and reproduce

Lumbricus has a streamlined body with no projecting structures, helping it move through the soil

Posterior end: dorsoventrally flattened

Anterior end: tapered

Clitellum or “saddle” : secretes a cocoon in which

eggs are deposited

Lumbricus: 4 pairs of chaetae in each segment:

Chaetae are used: during locomotion for gripping the soil for gripping the sides of the burrow if attacked by a

predator

except the first and the last

2 pairs positioned ventrally

2 pairs positioned ventrolaterally

The prostomium

is a small rounded structure without sensory appendages, overlying the mouth

Lumbricus feeds on:detritus (fragments of decomposing organic

material) by swallowing soil

the majority of the soil passes straight through the worm, much of it eventually being deposited as ‘worm casts’ on the ground surface

worm casts

Secretions of coelomic fluid and mucus keep the worm’s thin cuticle

This moisture:1) prevents desiccation 2) improves gaseous exchange3) acts as a lubricant for movement through the soil

Lumbricus is hermaphroditeTwo worms exchange sperm

and both are fertilised.

Sex organs are grouped at the anterior end of each

worm.

Main features of the class Oligochaeta (The Oligochaetes)

1. Inhabit freshwater or damp earth.2. No distinct head.3. Few chaetae – in pairs or single, no parapodia. 4. Clitellum or “saddle” which secretes a cocoon in

which eggs are deposited.

[diagnostic feature:

no parapodia]