Animalia 2009

P. C. G. H. S. LOWER 6 BIOLOGY

Compiled & prepared By

Yeap Chee Beng

Kingdom Animalia • • • •

• • Body plan Eukaryotic – basic structure Multicellular and functional Heterotrophic design of body Cells specialized • Animals have for specific diverse body functions plans

Most animals – are capable of locomotion at some time during life cycle – can respond adaptively to external stimuli – can reproduce sexually

Sexual Reproduction • Sperm and egg unite (zygote) • Zygote undergoes cleavage – cell divisions produce hollow ball of cells (blastula) • Blastula undergoes gastrulation – forms embryonic tissues

Marine Environments • Provide – relatively stable temperatures – buoyancy – readily available food

• Fluid and salt balance – more easily maintained than in fresh water

• Disadvantages: – currents and other water movements

Fresh Water • Provides – less constant environment – less food • Animals must osmoregulate – fresh water is hypotonic to tissue fluid

Terrestrial Animals • Have adaptations that – protect them from drying out – protect them from temperature changes – protect their gametes and embryos

How do biologists use structural characters (variations in body symmetry, number of tissue layers, type of body cavity) and patterns of early development to infer relationships among animal phyla?

Symmetry • Cnidarians and ctenophores are closely related – because they share radial symmetry – most other animals exhibit bilateral symmetry

• Cephalization (development of head) – evolved with bilateral symmetry

Radial and Bilateral Symmetry

In radial symmetry, multiple planes can be drawn through the central axis; each divides the animal into two mirror images. Radial symmetry (top view)

In radial symmetry, multiple planes can be drawn through the central axis; each divides the animal into two mirror images.

Radial symmetry (side view)

Dorsal Frontal section

Cross (or transverse) section

Caudal

Posterior

Anterior

Cephalic

Ventral

Bilateral symmetry (lateral view)

Dorsal Sagittal section

Medial Frontal Lateral In bilateral symmetry, the head end of the section animal is its anterior end, and the opposite end is its posterior end. The back of the animal is its dorsal surface, and the belly is its ventral surface. The diagrams also illustrate various ways the body can be sectioned (cut) to study its internal structure. A sagittal section Ventral (lengthwise vertical cut) divides the animal into right and left parts. A frontal, or longitudinal, cut (lengthwise horizontal) divides the body into dorsal and ventral parts. Bilateral symmetry (front view)

Other Structural Characters • Relationships can be based on – level of tissue development – type of body cavity • Embryonic tissues (germ layers)

Coelom Formation

Schizocoely — characteristic of protostomes

Enterocoely — characteristic of deuterostomes

Ectoderm Developing mesoderm Blastopore

Ectoderm Presumptive mesoderm Enterocoelic pouch

Endoderm Mesoderm Ectoderm Developing coelom (Schizocoel)

Ectoderm

Endoderm

Gut

Ectoderm

Endoderm Mesoderm Gut

Gut

Coelom (Enterocoel)

Coelom Mesoderm

Gut

Endoderm

Mesentery Epidermis (ectoderm)

Coelom Muscle layer (mesoderm) Gut

Peritoneum (mesoderm)

Two types of coelom formation • The coelom originates in the embryo from blocks of mesoderm that split off from each side of the embryonic gut. • In protostomes, the coelom typically forms by the process of schizocoely, in which the mesoderm splits. The split widens, forming a cavity that becomes the coelom. • In enterocoely, characteristic of deuterostomes, the mesoderm outpockets from the gut, forming pouches. The cavity within these pouches becomes the coelom. • Ectoderm is shown in blue, endoderm in yellow.

Germ Layers • Outer layer (ectoderm) – gives rise to body covering, nervous system

• Inner layer (endoderm) – lines the gut and other digestive organs

• Middle layer (mesoderm) – gives rise to most other body structures

Body Plans • The germ layer from which each tissue was derived is indicated in parentheses. Ectoderm is shown in blue, mesoderm in red, and endoderm in yellow. Epidermis (from ectoderm) Muscle layer (from mesoderm) Mesenchyme (gelatin-like tissue)

Epithelium (from endoderm)

(a) Acoelomate — flatworm (liver fluke)

Body Plans

Pseudocoelom Epidermis (from ectoderm) Muscle layer (from mesoderm)

Epithelium (from endoderm)

(b) Pseudocoelomate—nematode.

Body Plans

Coelom Epidermis (from ectoderm) Muscle layer (from mesoderm) Peritoneum (from mesoderm)

Epithelium (from endoderm) Mesentery (from mesoderm)

(c) True coelomate—vertebrate.

Bilateral Symmetry • Acoelomate – no body cavity • Pseudocoelomate – body cavity not completely lined with mesoderm • Coelomate, (animal with true coelom) – body cavity completely lined with mesoderm

Bilateral Animals Two major evolutionary branches: • Protostomia – mollusks, annelids, arthropods • Deuterostomia – echinoderms, chordates

Blastopore • Opening from embryonic gut to outside • In protostomes – develops into the mouth • In deuterostomes – becomes the anus

Cleavage 1 • Protostomes – undergo spiral cleavage – early cell divisions diagonal to polar axis • Deuterostomes – undergo radial cleavage – early cell divisions either parallel or at right angles to polar axis – cells lie directly above or below one another

Spiral and Radial Cleavage • The pattern of cleavage can be appreciated by comparing the positions of the purple cells in (a) & (b).

Cleavage 2 • Protostomes – undergo determinate cleavage – fate of each embryonic cell is fixed very early • Deuterostomes – undergo indeterminate cleavage – fate of each embryonic cell is more flexible

Relationships based on Structure

Evolutionary relationships of major animal phyla, based on structure. The bilateral animals are grouped by several criteria, including type of body cavity: acoelomate, pseudocoelomate, or coelomate.

KEY CONCEPTS • Biologists classify animals based on their body plan and features of their early development

Phylum Porifera • Sponges – animals characterized by flagellate collar cells (choanocytes)

• The only members of the Parazoa – sister group of Eumetazoa

Sponge Structure • Sponge body – sac with tiny openings for water to enter – central cavity (spongocoel) – open end (osculum) for water to exit

• Sponge cells – loosely associated – do not form true tissues

Sponge Structure

Choanoflagellate ancestor

Sponge structure. (a) Tube sponges (Spinosella plicifera) from the Caribbean, attached to the coral reef substrate.

Deuterostomia

Ecdysozoa

Lophotrochozoa

Radiata

Porifera

Parazoa

Incurrent pores

Water movement

Osculum

Spongocoel

Epidermal Sponge structure. cell (b) Diagram of a simple sponge cut to expose its organization. Collar cells (choanocytes) beat their flagella, producing a current of water that enters through the pores. The water passes Porocyte through the spongocoel and exits through the osculum. Food particles in the stream of water Spicule are trapped by the collars. Microvillus Nucleus Collar cell Amoeboid cell in mesohyl Flagellum Collar

KEY CONCEPTS • Sponges (phylum Porifera) are characterized by collar cells and by loosely associated cells that do not form true tissues

Phylum Cnidaria • Characterized by – radial symmetry – two tissue layers – cnidocytes (cells containing nematocysts)

Nematocysts

When cnidarian stinging cells (cnidocytes) are stimulated, the nematocyst discharges, ejecting a thread that may entangle or penetrate the prey. Some nematocysts secrete a toxic substance that immobilizes the prey.

Cnidocyte

Nucleus Thread Capsule

Nematocyst (not discharged) Cnidocil (trigger)

Thread

Nematocyst (discharged)

Phylum Cnidaria • Gastrovascular cavity – with single opening for mouth and anus

• Nerve cells form irregular, nondirectional nerve nets – connect sensory cells with contractile and gland cells

Cnidarian Structure • Hydra

Tentacles Cnidocytes (stinging cells)

1 mm

Mouth

Bud

Cnidarian Structure • Hydra • a freshwater hydrozoan.

Gastrovascular cavity Epidermis Mesoglea Gastrodermis

Egg (ovum)

Ovary

Cnidaria Life Cycle • Sessile polyp stage – form with dorsal mouth surrounded by tentacles

• Free-swimming medusa (jellyfish) stage

1

Cnidaria (Obelia) Life Cycle

Reproductive polyps produce medusae by budding asexually Mouth Tentacle

Medusae

Feeding polyp

2 Medusa bud Reproductive polyp

Egg

Sperm

3

Gastrovascular cavity

Free-swimming medusae reproduce sexually.

Planula larva

Zygote develops into ciliated planula larva.

Polyp colony 5 Colony grows as new polyps bud and remain attached.

4 Young polyp colony

Obelia, a marine colonial hydrozoan.

Larva develops into polyp that forms new colony.

4 Classes of Phylum Cnidaria 1. Class Hydrozoa (hydras, hydroids, Portuguese man-of-war) – typically polyps – may be solitary or colonial

2. Class Scyphozoa (jellyfish) – generally medusae

4 Classes of Phylum Cnidaria 3. Class Cubozoa (“box jellyfish”) – have complex eyes that form blurred images

4. Class Anthozoa (sea anemones, corals) – polyps – may be solitary or colonial – differ from hydrozoans in organization of gastrovascular cavity

Cnidarians • Polyp and medusa body forms of cnidarians

Choanoflagellate ancestor

Deuterostomia

Ecdysozoa

Lophotrochozoa

Ctenophora

Cnidaria

Parazoa

Radiata

Mouth

Epidermis Mesoglea Gastrodermis Gastrovascular cavity

Class Hydrozoa (polyp)

Mouth

Mesoglea Gastrodermis

Epidermis Gastrovascular cavity

Class Scyphozoa (medusa)

Mouth Epidermis

Mesoglea Gastrodermis Gastrovascular cavity

Class Anthozoa (polyp)

KEY CONCEPTS • Members of phylum Cnidaria (hydras, jellyfish, sea anemones) are characterized by – radial symmetry, – two tissue layers, and – cnidocytes, • cells that contain stinging organelles

Phylum Ctenophora • Comb jellies – – – –

fragile, luminescent marine predators biradial symmetry eight rows of cilia that resemble combs tentacles with adhesive glue cells

Comb Jelly

KEY CONCEPTS • Members of phylum Ctenophora (comb jellies) have biradial symmetry, two tissue layers, eight rows of cilia, and tentacles with adhesive glue cells

Coelom • True coelom is a fluid-filled body cavity – completely lined by mesoderm between digestive tube and outer body wall

• Allows tube-within-a-tube body plan – body wall is outer tube – inner tube is digestive tube

Coelom • An enclosed compartment (or series of compartments) of fluid under pressure • Serve as hydrostatic skeleton – contracting muscles push against tube of fluid

• A space in which internal organs develop – including gonads

• Helps transport materials • Protects internal organs

KEY CONCEPTS • Evolution of the coelom has been associated with important innovations in body plan, including – cephalization, – the tube-within-a-tube body plan, – compartmentalization and segmentation

Protostomes • Characterized by – spiral cleavage – determinate cleavage – development of mouth from blastopore

Two Branches of Protostomes • Lophotrochozoa – platyhelminths, nemerteans, mollusks, annelids, lophophorate phyla, rotifers

• Ecdysozoa – nematodes (roundworms) and arthropods

• Protostomes are a monophyletic group that gave rise to two major clades: Lophotrochozoa and Ecdysozoa

Phylum Nemertea (Ribbon Worms) • Characterized by proboscis – muscular tube for capturing food, defense

• Reduced coelom (rhynchocoel) – space surrounding proboscis

• Nemerteans have – tube-within-a-tube body plan – complete digestive tract with mouth and anus – a circulatory system

Nemerteans

Phylum Platyhelminthes (Flatworms) • Acoelomate animals with – – – –

bilateral symmetry cephalization 3 definite tissue layers well-developed organs

• Ladder-type nervous system – sense organs – simple brain composed of two ganglia – 2 nerve cords that extend the length of body

• Many are hermaphrodites • Protonephridia – single animal produces both sperm and eggs

– function in osmoregulation and disposal of metabolic wastes

3 Classes of Phylum Platyhelminthes • Class Turbellaria – free-living flatworms, including planarians

• Classes Trematoda and Monogenea – parasitic flukes

• Class Cestoda – parasitic tapeworms

Planarian

Choanoflagellate ancestor

Deuterostomia

Ecdysozoa

Rotifera

Lophophorate phyla

Annelida

Mollusca

Nemertea

Platyhelminthes

Radiata

Parazoa

Lophotrochozoa

Ganglia

Auricle

Auricle Eyespot Nerve Gastrovascular cavity Pharynx Sheath surrounding pharynx Mouth

1 mm

Pharyngeal sheath cavity Pharyngeal cavity

Inner muscle layer of pharynx Outer muscle layer

Muscle

Epidermis

Sperm mass

Ventral nerve cords

Adhesive gland Cilia Muscle layers

Body wall composed of epidermis, circular muscle, and longitudinal muscle

Parasitic Flukes and Tapeworms • Typically have suckers or hooks – for holding on to their hosts

• Have complicated life cycles – intermediate hosts – large numbers of eggs

Larvae make their way to 2 circulatory system, where they mature. During reproduction, which takes place in veins, male holds female in a long groove.

1 Larvae

burrow through skin.

1 mm

7 Finally, fork-

tailed larvae (cercariae) develop and leave snail.

Life cycle of the blood fluke (Schistosoma)

3

Eggs pass into intestine.

4 Eggs containing

developing embryos are excreted with faeces. 6

Larvae must enter a second host, a freshwater snail. After burrowing into tissues of snail, larvae develop into a form that reproduces asexually.

5 If they find their way to fresh water, the eggs hatch, releasing freeswimming larvae (miracidia).

Tapeworm

Cephalization • Evolution of a head – concentration of sense organs and nerve cells (simple brain) at anterior end – (Flatworms show beginnings of cephalization)

• Increases effectiveness of bilateral animal – to actively find food, shelter, mates – to detect enemies

Phylum Mollusca • Soft-bodied animals – usually covered by a shell

• Ventral foot – for locomotion

• Mantle – covers visceral mass (body organs)

Mollusks • Most have open circulatory system – Cephalopods have closed circulatory system

• Most have rasplike radula for feeding – Bivalves are suspension feeders

• Most marine mollusks have free-swimming, ciliated trochophore larva

Trochophore Larva

• The first larval stage of a marine mollusk, the trochophore larva, is also characteristic of annelids. • Just above the mouth a band of ciliated cells functions as a swimming organ and, in some species, collects suspended food particles.

Digestive tract

Cilia

Mouth Nephridium Mesodermal cells

Anus

Trochophore Larva

Class Polyplacophora • Includes marine chitons • Shells consist of 8 overlapping plates

The mollusk body plan. (a) Chitons are sluggish marine animals with shells composed of eight overlapping plates. • This sea cradle chiton (Toni cella lineata), which reaches about 5 cm (2 in) in length, inhabits rocks covered with corraline algae in coastal waters off the U.S. Pacific Northwest. Class Polyplacophora

Shell Digestive tract

Class Gastropoda • Largest group of mollusks – snails, slugs, and their relatives

• Body undergoes torsion – a twisting of the visceral mass

The mollusk body plan. (b) The broad, flat foot of the gastropod is an adaptation to its mobile lifestyle. • The mystery snail (Pomacea bridgesi) inhabits fresh water and can be found burrowing in the mud. Class Gastropoda Shell

Foot

Digestive tract

Torsion

Class Bivalvia • Includes aquatic clams, scallops, oysters • Two-part shell – hinged dorsally – encloses bodies

• Suspension feeders

The mollusk body plan. (c) The compressed body of the horseneck clam (Tresus capax) is adapted for burrowing in the North Pacific mud. • Its shell grows to about 20 cm (8 in) in length. Class Bivalva Shell

Digestive Foot tract

Clam

Excurrent siphon Incurrent siphon

Internal anatomy of a clam • The two shells of a bivalve hinge dorsally and open ventrally.

Class Cephalopoda • Includes squids, octopods, Nautilus • Active, predatory swimmers • Tentacles surround the mouth – located in the large head

The mollusk body plan. (d) The squid body is streamlined for swimming. • To avoid being seen by potential predators, the squid can change color to blend with its background. • This northern shortfin squid (Illex illecebrosus), which grows to a mantle length of up to about 31 cm (about 1 ft), inhabits the North Atlantic ocean.

Class Cephalopoda Tentacles (modified foot)

Internal shell

Digestive tract

Phylum Annelida (Segmented Worms) • Aquatic worms, earthworms, leeches • Conspicuously long bodies • Segmentation – both internally and externally

• Large, compartmentalized coelom – serves as hydrostatic skeleton

Annelids

Earthworm

Leeches

Class Polychaeta • Marine worms with parapodia – appendages for locomotion, gas exchange

• Parapodia have many setae • Well-defined head with sense organs – unlike other annelids

Class Oligochaeta • Earthworms • Characterized by few short setae per segment • Body divided into > 100 segments – separated internally by septa

Class Hirudinea • Leeches • Characterized by absence of setae and appendages • Parasitic leeches have suckers – for holding on to their host

The Lophophorate Phyla • Marine animals with a lophophore – brachiopods, phoronids, bryozoans

• Lophophore – ciliated ring of tentacles surround the mouth – specialized to capture particles in water

Lophophorates • Phylum Brachiopoda

• Phylum Phoronida

• Phylum Bryozoa

Phylum Rotifera

Learning Objective • What are the distinguishing characteristics of phylum Nematoda?

Phylum Nematoda (Roundworms) • Highly successful ecdysozoans • Pseudocoelom • Body covered by tough cuticle – helps prevent desiccation

Phylum Nematoda (Roundworms) • Parasitic nematodes in humans – – – –

Ascaris hookworms trichina worms pinworms

Ascaris

Mouth

Pharynx

Dorsal nerve

The roundworm Ascaris. (a) Note the complete digestive tract that extends from mouth to anus. (b) This cross section through Ascaris shows the tube-within-a-tube body plan. The protective cuticle that covers the body helps the animal resist drying.

Excretory canal Excretory gland

Pharynx

Muscle of pharynx wall

Pseudocoelom Uterus Ovary Intestine Excretory canal

Vulva Muscle layer Epidermis

Ventral nerve

Cuticle

(b) Cross section

(a) Longitudinal section

Anus

Phylum Arthropoda • Segmented animals with paired, jointed appendages • Armorlike exoskeleton of chitin • Molting necessary for arthropod to grow

Phylum Arthropoda • Open circulatory system – dorsal heart, pumps hemolymph

• Aquatic forms have gills for gas exchange • Terrestrial forms have either tracheae or book lungs

Trilobites • Extinct marine arthropods – covered by hard, segmented shell

• Each segment had a pair of biramous appendages with two jointed branches – inner walking leg – outer gill branch

Trilobites

Subphylum Myriapoda • 2 Classes – Chilopoda (centipedes) – Diplopoda (millipedes)

• Uniramous (unbranched) appendages • Single pair of antennae

Myriapods

Subphylum Chelicerata • Merostomes (horseshoe crabs) and Arachnids (spiders, mites, and relatives) • Body with cephalothorax and abdomen • 6 pairs of uniramous, jointed appendages – 4 pairs serve as legs

Subphylum Chelicerata • First appendages are chelicerae – second are pedipalps

• Appendages adapted for manipulation of food, locomotion, defense, copulation • No antennae, no mandibles

Chelicerates

Subphylum Crustacea • Lobsters, crabs, shrimp, pill bugs, barnacles • Body with cephalothorax and abdomen • Most have five pairs of walking legs • Appendages are biramous

Subphylum Crustacea • Two pairs of antennae – sense taste and touch

• Third appendages are mandibles – for chewing

• Two pairs of maxillae – posterior to mandibles – manipulate and hold food

Crustaceans

Lobster

Cephalothorax Abdomen Thorax

Head

Eye Fifth walking leg

Anatomy of the lobster. (a) Like other decapods, the spiny lobster (Panulirus argus) has five pairs of walking legs. The first pair of walking legs is modified as chelipeds (large claws).

Tail fan

Fifth walking leg

Second walking leg Mouth

Third maxilliped Cheliped

First antenna Second antenna

Swimmerets First swimmeret (used by male in copulation)

Anatomy of the lobster. (b) Ventral view of a lobster. Note the variety of specialized appendages.

Subphylum Hexapoda

Anatomy of the grasshopper.

Head

Thorax

Abdomen

Forewing

Antenna Simple eye Compound eye

Sound receptor

Spiracles

(a) External structure. Note the three pairs of segmented legs.

Hindwing

Insects • • • • •

Body with head, thorax, and abdomen Uniramous appendages Single pair of antennae Tracheae for gas exchange Malpighian tubules for excretion

Grasshopper Ovary Digestive gland

Heart

Anus

Brain

Nerve cord Malpighian tubules (b) Internal Anatomy.

Intestine Genital opening

Insect Adaptations • Versatile exoskeleton • Metamorphosis – transition from one • Segmentation developmental form to • Specialized jointed another appendages – reduces intraspecific • Highly developed sense competition organs • Ability to fly • Insects have developed – effective reproductive strategies – effective mechanisms for defense, offense – ability to communicate

Metamorphosis

Deuterostome Relationships • All: – Have radial cleavage – Cleavage is indeterminate – Triploblastic – Coelom forms from cavities in the mesoderm – Blastopore becomes the anus; mouth develops from a second opening at the anterior end • Two major groups: – Echinoderms – Chordates

•

The deuterostomes include both invertebrates and vertebrates • Relationships among the deuterostomes: 1. Echinoderms 2. Chordates – The fish – The amphibians – The amniotes • Reptiles • Birds • Mammals

Deuterostomes • Shared derived characters – radial, indeterminate cleavage – blastopore becomes anus – larva have a loop-shaped ciliated band used for locomotion

• The echinoderms and the chordates are the two most successful deuterostome lineages in terms of diversity, number of species, and number of individuals

Phylum Echinodermata • Marine; ~13,000 species; throughout all oceans • Six classes: – Crinoidea • Sea lilies and feather stars – Asteroidea • Sea stars – Ophiuriodea • Brittle stars – Echinoidea • Sea urchins and sand dollars – Holothuria • Sea cucumbers – Concentricycloidea • Sea daisies

Echinoderm Anatomy • Larvae are bilateral, ciliated and free-swimming • Pentaradial symmetry develops as the animal settles • Develops an endoskeleton (internal skeleton) of calcium carbonate plates and spines • Some of the endoskeleton projects through the outer skin giving rise to name: spiny skinned (echinoderm) • Modified spines call pedicellariae on the surface have tiny pincers that clean the surface • Hydraulic water vascular system is a system of fluid filled canals – Leads to many tiny tube feet that extend under pressure and stick to surfaces, used for locomotion, prey capture – Ampulla, muscular sac, used to pressurize the water vascular system • Have well-developed coelom, transports materials. • No excretory organs • Simple nervous system, nerve ring around mouth

Class Asteroidea • Commonly named as sea stars – central disc with five or more arms – use tube feet for locomotion

Sea Star Body Plan

Body plan of a sea star

Stomach

Digestive gland Anus

Ampulla

Tube feet

Gonad A sea star viewed from above, with its arms in various stages of dissection. Similar structures are present in each arm. The two-part stomach is in the central disc with the anus on the aboral (upper) surface and the mouth beneath on the oral surface.

Spine Dermal gill Pedicellariae

Class Holothuria • Commonly named as sea cucumbers • Look much like a cucumber, are various colours • Body is flexible, saclike with pentameric symmetry around the long axis • Better developed circulatory system, transports oxygen and nutrients • Sluggish, benthic, some burrow • Food is trapped in mucus that covers tentacles • Will eviscerate; ejective the digestive trace, respiratory structures and gonads under unfavorable conditions; • Will regenerate lost parts later

Class Holothuroidea

• Sea cucumbers – elongated flexible bodies – circle of modified tube feet surrounds mouth

Phylum Chordata • At some time during life cycle have – flexible, supporting notochord – dorsal, tubular nerve cord – pharyngeal (gill) slits – muscular postanal tail – endostyle (or thyroid gland)

The Chordates • All have – Notochord: dorsal, stiff rod, supports body – Dorsal tubular nerve cord, not ventral – Pharyngeal slits in the embryo • Alternating branchial arches and grooves develop, look like gills • Probably a vestigial characteristic from filter feeding which was modified for gas exchange – Most have a muscular, post anal tail

Vertebrate Adaptations • Endoskeleton based upon a vertebral column, forms skeletal axis • Made of vertebrae (either bone or cartilage or both) • Anterior end has a cranium or brain case • Structures in vertebrates derived from neural crest cells, found only in vertebrates and early in development • Vertebrate evolution characterized by exceptional cephalization – brain more elaborate, well-developed sense organs • Two pairs of appendages: fins / legs • Closed circulatory system, ventral heart and blood with haemoglobin and efficient oxygen carrier • Usually have complex endocrine glands

One View of Chordate Affinities • ~ 48,000 species • A traditional view of evolutionary relationships • Six classes of fish, four classes of tetrapods (aquatic tetrapods such as penguins evolved from terrestrial forms)

Chordate Body Plan

supporting structures

Evolution of Jaws gill slit

• First fishes lacked

Early jawed fish (placoderm)

jaws • Jaws are modifications of anterior gill supports

Early jawless fish (agnathan)

jaw spiracle jaw support Modern jawed fish (shark)

jaw

Existing Jawless Fishes • Cylindrical body

• No paired fins

• Cartilaginous skeleton Hagfish

tentacles

Lamprey

gill slits (twelve pairs) gill openings (seven pairs)

mucous glands

Jawed Fishes

• Most diverse and numerous group of vertebrates • Two classes: – Chondrichthyes (cartilaginous fishes) – Osteichthyes (bony fishes)

Cartilaginous Fishes

Modern Bony Fishes

Cartilaginous Fishes: Bony Fishes: Class Chondrichthyes Class Osteichthyes • Most are marine predators • Cartilaginous skeleton • Main groups: – Skates and rays – Sharks – Chimaeras (ratfishes)

• Includes 96 percent of living fish species • Three subclasses: – Ray-finned fishes – Lobe-finned fishes – Lung fishes

The Cartilaginous Fish: Class Chondricthyes • Includes sharks, rays and skates • Mainly marine, a few freshwater – Can be very small but the whale shark is the largest known fish • Rays and skates are greatly flattened • All retain embryonic cartilaginous skeletons • Have paired jaws and two pairs of fins • Skin has placoid scales, really a toothlike structure; the mouth contains large ones that serve as teeth – Placoid scales are homologous to other vertebrate teeth

Shark Anatomy • Sharks are well adapted to swimming • Very elongate, low friction bodies • Body shape and fins supplies lift; body is denser and will sink unless it swims

Shark Organ Systems • Well-developed brain • Keen chemosensory organs • Electroreceptors sense weak electrical fields of the muscles of prey • Lateral line organ is sensitive to mechanical disturbances • No lungs, but 5-7 paired gills • Long pharynx but short straight intestine leading to a cloaca, which receives metabolic wastes and urine; – is reproductive organ in females

Reproduction in Chondrichthys • Separate sexes, internal fertilization • Males have modified pelvic fin called a clasper that transfers sperm to the female • Eggs fertilized in the upper part of the oviducts – are coated with covering as they move down the oviduct

• Skates and some sharks are oviparous (egg-laying) • Many sharks are ovoviviparous, – in that they hatch within the mother’s body

• Some sharks are viviparous (live-bearing)

The Bony Fishes • Bony fish have advantages over cartilaginous fish – Bone is strong – Provides support – Stores calcium – Bony fish have tough calcareous scales – Fins are tough, supported by long rays of bone/cartilage – Operculum (gill flap), strong and protects head – Bony fish usually have very large numbers of young • In the Devonian, diverged into two groups – Lobe-finned fish (Sarcoptergii) – Ray finned fish (Actinoptergii)

Bony Fish Structure

Living Amphibian Groups • Frogs and toads • Salamanders • Caecilians

Amphibian Groups • First tetrapods (land vertebrates) were labyrinthodonts – Some very large size of modern crocodilians – Heavy-bodied, massive tails – Legs just strong enough to crawl about – Thought to have given rise to modern frogs and salamanders • Modern amphibia classified into three Orders – Urodela (visible tail) • Salamanders, newts and mudpuppies – Anura (no tail) • Frogs and toads – Apoda (no feet) • Caecilians, which are shaped like worms

Amphibians Have Metamorphosis • Amphibians undergo metamorphosis from larva to adult • Most have tadpoles as larvae – Tails, gills, feed on plants – Thyroid gland hormones regulate the change – Gill and gill slits disappear – Tail is resorbed – Limbs appear – Food shifts to carnivorous diet • changes occur in digestive tract – Mouth widens, tongue develops – The ear drum and eyelids appear and the eye changes shape

Evolution of Amphibians

Early Amphibians

Modern Amphibians • All require water at some

• Lungs became more effective • Chambers of the

stage in the life cycle; most lay eggs in water • Lungs are less efficient

heart became

than those of other

partially separated,

vertebrates

making circulation more efficient

• Skin serves as respiratory organ

Adult Amphibians • Have primitive lungs • Have moist skin that allows cutaneous gas exchange • Mucus maintains wet skin and allows escape from predators – Sometimes mucus is poisonous • Have three-chambered heart – Two atria receive blood – One ventricle pumps it to the arteries – Two circulatory systems: • Systemic to various tissues and organs that use oxygen • Pulmonary to the lungs and skin where it is recharged with oxygen

Terrestrial Vertebrates • Amniotes – include reptiles, birds, mammals

• Amniotic egg (with shell and amnion) – important adaptation for life on land

• Amnion (membrane) – forms fluid-filled sac around embryo

Amniotic Egg

Amniotes • Evolution of the amniotic egg was critical to advancement beyond amphibia • The egg contains fluid-filled sac called the amnion – Keeps embryo wet

• From the amniotic egg organisms were able to diverge yet again – to reptiles, birds and mammals • Amniotic egg has – Yolk – nutrient stores for embryo – Chorion and allantois – for gas exchange and waste storage (allantois)

Amniotes • Have body coverings that minimize water loss • Decreases gas exchange across body; requires better lungs and efficient blood circulatory systems • Conserve water through excretion of wastes in the kidney • Conversion of toxic ammonia to uric acid in birds and reptiles is a water-saving mechanism; to urea in mammals

4 Groups of Extant Reptiles 1. Turtles, terrapins, tortoises

4 Groups of Extant Reptiles 2. Lizards, snakes, amphisbaenians

4 Groups of Extant Reptiles 3. Tuataras

4 Groups of Extant Reptiles 4. Crocodiles, alligators, caimans, gavials

Modern Reptiles • Reproduction – Leathery shell around egg – Internal fertilization occurs first, then production of the shell in the oviduct – Requires a copulatory organ – the penis

• Are ectothermic – require heat from outside source • Dry scaly skin – Requires good lung, circulatory system – Reptiles have 3-chambered, efficient heart – Crocodilians have 4-chambered heart, • which is more efficient and keeps the oxygenated blood separate from the oxygen-depleted blood

venom gland

Lizards and Snakes • Largest order (95% of living reptiles) • Most lizards are insectivores with small peglike teeth • All snakes are carnivores with highly movable jaws

hollow fang

Lizards and Snakes • Order Squamata – Lizards usually run on four legs • Many rows of scales, flexible armor • Wide range of sizes, from a few cm to several m – Snakes have lost limbs secondarily • Very elongate, no eyelids, no external ear • Forked tongue is sensory • Some (pit vipers) have infrared sensing organ • Kill by constriction, or by poisons

Class Aves (Modern Birds)

Class Aves (Modern Birds) • The only group to have feathers • Found in all habitats; aquatic, terrestrial & marine • Some very small (hummingbirds) whereas the largest are ostriches (~ 2 m tall) • Lay eggs like reptiles • Anterior limbs usually specialized for flight (or swimming in some species) • Posterior limbs for running, perching or swimming • Very strong bones, yet very light • Beak replaces teeth and the breastbone is keeled to allow attachment of very large pectoral flight muscles • Are endothermic – ‘warm blooded’ – Supports energetic life style

Avian Respiratory Apparatus • Birds have extraordinary lungs – Have extensions called air sacs, occupy spaces between internal organs and some bones

• Have one-way flow of air through respiratory system • Very efficient four-chambered heart • All work together to support very high metabolic rate, needed for the stress of flying

• Waste – Excrete waste as uric acid – Is solid waste, passed to cloaca where it is vented often – Saves water, keeps weight down

• Adapted to many environments and life styles through adaptations to beaks, feet, wings, and through behaviour • Eat energy-rich foods such as fruit • Partition feeding effort specifically for certain prey, such as rodents, rabbits, etc • Birds have a crop, which incorporates pebbles, sand, etc – to grind up food to increase surface area and speed digestion – also they don’t have to grind food with teeth

• Very fast nervous system – good vision, allows fast reaction to changing environment

• Exceptionally vocal, make calls to find mates, lay out territories • Tend to be brightly colored to attract mates, advertise territory, from afar

Placental Mammals (Subclass Eutheria) • Characterized by placenta – for exchange between embryo and mother

Class Mammalia • • • • •

Hairy Mammary glands to produce milk for young Differentiated teeth used for cutting, grinding Muscular diaphragm pulls air in Very complex nervous system with well developed brain • Internal fertilization, and except for monotremes, viviparous • Placenta transfers nourishment and waste to/from developing young

Placental Mammals • Develop placenta, which is interface between mother and young – Provides nutrition and removes wastes – Forms from embryonic membranes and the mother’s uterine wall – Bloods don’t mix but come very close – Exchange gases, nutrients

• Allows more mature young to be born – Typically newly-born young interact with others in the family soon after birth

Biodiversity in Malaysia • Malaysia is one of the global biodiversity hotspot – A relatively small area with an exceptionally large and diverse concentration of species – 60% of the world’s known species of plants & animals are located here

• Ecosystems with high biodiversity are more productive, more stable & able to withstand disturbances compared to ecosystems with reduced biodiversity

Biodiversity in Malaysia • Many species in Malaysia are endemic – Not found anywhere else in the world – Highly susceptible to habitat loss (caused by human activities)

• Different types of ecosystems – – – – –

Lowland forest Montane forest Mangrove forest Peat swamp forest Sulu-Sulawesi seas

Threat of Declining Biodiversity • Habitat destruction • Invasion by new species • Pollution • Overexploitation • Fish bombing • Illegal logging

Implication of the threat to biodiversity •

Cause flooding & contaminate water supplies

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Climatic change

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Loss genetic variability

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Economic loss

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Play a vital, but sometimes unrecognized role in the balance of nature

Conservation of Biodiversity • In situ conservation – Parks, reserves, national parks, sanctuaries

• Ex situ conservation – Zoos, botanical gardens, aquariums, gene banks – Techniques used in this approach: • Captive breeding of endangered organisms & consequent reintroduction into the wild • Artificial insemination and host mothering (or embryo transfer) • Cloning