UNIT 4: BIODIVERSITY OF ANIMALS:

INVERTEBRATES

( Campbell and Reece, 2010: Chapter 32 and 33)

Welcome to Your Kingdom

• The animal kingdom extends far beyond humans and other animals we may encounter

• 1.3 million living species of animals have been identified

• Invertebrates (animals that lack a backbone) account for 95% of known animal species.

EARLY EMBRYONIC DEVELOPMENT IN ANIMALS

Most animals reproduce sexually, with the diploid stage usually dominating the life cycle

After a sperm fertilizes an egg, the zygote undergoes rapid cell division called cleavage

Cleavage leads to formation of a blastula The blastula undergoes gastrulation,

forming a gastrula with different layers of embryonic tissues.

EARLY EMBRYONIC DEVELOPMENT IN ANIMALS

Fig. 32-2-1

Zygote

Cleavage

Eight-cell stage

EARLY EMBRYONIC DEVELOPMENT IN ANIMALS

Fig. 32-2-1

Zygote

Cleavage

Eight-cell stage

Fig. 32-2-2

Zygote

Cleavage

Eight-cell stage

Cleavage

Blastula

Cross sectionof blastula

Blastocoel

EARLY EMBRYONIC DEVELOPMENT IN ANIMALS

Fig. 32-2-1

Zygote

Cleavage

Eight-cell stage

Fig. 32-2-2

Zygote

Cleavage

Eight-cell stage

Cleavage

Blastula

Cross sectionof blastula

Blastocoel

Fig. 32-2-3

Zygote

Cleavage

Eight-cell stage

Cleavage

Blastula

Cross sectionof blastula

Blastocoel

Gastrulation

BlastoporeGastrula

Archenteron

EctodermEndoderm

Blastocoel

• Many animals have at least one larval stage.

• A larva is sexually immature and morphologically distinct from the adult; it eventually undergoes metamorphosis.

2. RELATIONSHIP BETWEEN BODY PLAN AND GROUPING

OF ANIMALS IN PHYLA

• Zoologists sometimes categorize animals according to a body plan.

• A body plan is a set of morphological and developmental traits, integrated into a functional whole living animal.

CHARACTERISTICS WHICH CHARACTERISTICS WHICH EXPLAIN BODY PLANEXPLAIN BODY PLAN

• Symmetry

• Cephalization

• Tissues)

• Body cavities

• Protostome and Deuterostome development

A. SYMMETRY

• Animals can be categorized according to the symmetry of their bodies, or lack of it

• Some animals have radial symmetry

• Two-sided symmetry is called bilateral symmetry

RADIAL SYMMETRY

BILATERAL SYMMETRY

Bilaterally symmetrical animals have:

–A dorsal (top) side and a ventral (bottom) side

–A right and left side

–Anterior (head) and posterior (tail) ends

B. CEPHALIZATION

• Cephalization, the development of a head

C. TISSUES• Animal body plans also vary according to

the organization of the animal’s tissues• Tissues are collections of specialized

cells • During development, three germ layers

give rise to the tissues and organs of the animal embryo

• Ectoderm is the germ layer covering the embryo’s surface

• Endoderm is the innermost germ layer and lines the developing digestive tube, called the archenteron

• Mesoderm: middle layer of some body plans

GERM LAYERS ARE:

• Diploblastic animals have ectoderm and endoderm

• Triploblastic animals have an ectoderm, endoderm and intervening mesoderm layer.

D. BODY CAVITIES • Most triploblastic animals possess a body cavity

• A true body cavity is called a coelom and is derived from mesoderm

• Coelomates are animals that possess a true coelom

• A pseudocoelom is a body cavity derived from the mesoderm and endoderm

• Triploblastic animals that possess a pseudocoelom are called pseudocoelomates

• Triploblastic animals that lack a body cavity are called acoelomates

E. PROTOSTOME AND DEUTEROSTOME DEVELOPMENT • Based on early development, many animals can

be categorized as having protostome development or deuterostome development

• These two types of developments differ in regard to:

• Different cleavage• Different coelom formation• Fate of the blastopore

CLEAVAGE• In protostome development, cleavage is

spiral and determinate• In deuterostome development, cleavage is

radial and indeterminate• With indeterminate cleavage, each cell in the

early stages of cleavage retains the capacity to develop into a complete embryo

COELOM FORMATION

• In protostome development, the splitting of solid masses of mesoderm forms the coelom.

• In deuterostome development, the mesoderm buds from the wall of the archenteron to form the coelom.

FATE OF THE BLASTOPORE

• The blastopore forms during gastrulation and connects the archenteron to the exterior of the gastrula

• In protostome development, the blastopore becomes the mouth

• In deuterostome development, the blastopore becomes the anus

3. SYNOPTIC CLASSIFICATION OF THE ANIMAL KINGDOM

Kingdom: AnimaliaBranch 1: Mesozoa (fish parasites)

Branch 2: Parazoa (cellular) Phylum: Porifera (sponges)

Branch 3: Eumetazoa (multicellular)

Branch 3: Eumetazoa (multicellular)• Grade 1: Radiata (Radial symmetry, tissue level)

Phylum: Cnidaria hydras corals sea-anemones

• Grade 2: Bilateria (Bilateral symmetry, organ level, cephalisation)

Grade 2: Bilateria (Bilateral symmetry, organ level, cephalisation)

• Division 1: Protostomia

• Division 2: Deuterostomia

Division 1: Protostomia• Group 1: Acoelomata (no body cavity)

Phylum: Platyhelminthes (flat worms)

• Group 2: Pseudocoelomata (pseudo body cavity)

Phylum: Nematoda (round worms)

• Group 3: Eucoelomata

Phylum: Annelida (earthworms, leeches: Metamerism)

Phylum: Arthropoda (crabs, insects: Tagmatisation)

Phylum: Mollusca (slugs, snails)

Division 2: Deuterostomia

Phylum: Echinodermata sea stars seaurchins

Phylum: Chordata (vertebrates)

SUMMARY OF PHYLA• Phylum: Porifera (sponges)• Phylum: Cnidaria (Hydra, sea anemones)• Phylum: Platyhelminthes (flat worms)• Phylum: Nematoda (round worms)• Phylum: Annelida (earthworms, leeches)• Phylum: Arthropoda (crabs, insects)• Phylum: Mollusca (slugs, snails)• Phylum: Echinodermata (sea stars, sea urchins)• Phylum: Chordata (vertebrates)

Phylum: Porifera (sponges)• Sedentary animals (fixed in one position)• They live in both fresh and marine waters• Cellular level of development• Lack true tissues and organs• Asymmetrical

Phylum:Cnidaria (Hydra, sea anemones)

• True tissue – Eumetazoa• Both sessile and motile forms including jellies, corals, and

hydras• Diploblastic body plan• Radial symmetry• The basic body plan of a cnidarian is a sac with a central

digestive compartment, the gastrovascular cavity• A single opening functions as mouth and anus

• Carnivores that use tentacles to capture prey

• The tentacles are armed with cnidocytes, unique cells that function in defense and capture of prey

• Nematocysts are specialized organelles within cnidocytes that eject a stinging thread.

Phylum: Platyhelminthes (flat worms)

• Live in marine, freshwater, and damp terrestrial habitats.

• Triploblastic development • Acoelomates • Flattened dorsoventrally and have a

gastrovascular cavity• Gas exchange takes place across the surface• Protonephridia regulate the osmotic balance

Phylum: Nematoda (round worms)

• Found in most aquatic habitats, in the soil, in moist tissues of plants, and in body fluids and tissues of animals

• They have an alimentary canal, but lack a circulatory system

• Sexual Reproduction • Internal fertilization• Some species are parasites of plants and animals.

Phylum: Annelida (earthworms, leeches)

• Bodies composed of a series of fused rings or compartments - Metamerism

Phylum: Arthropoda (crabs, insects)• Found in nearly all habitats of the biosphereThe arthropod body plan consists of a

segmented body, hard exoskeleton (made of layers of protein and

the polysaccharide chitin jointed appendages

• The body is completely covered by the cuticle• When it grows, it molts its exoskeleton.• Includes: insects, crabs, spiders, millipedes, centipedes,

mites…

EXAMPLES OF ARTHROPODA ORGANISMS

Phylum: Mollusca (slugs, snails)• Includes snails and slugs, oysters and clams,

and octopuses and squids

• Most are marine, some inhabit fresh water and some are terrestrial

• Soft bodied animals, but most are protected by a hard shell.

Phylum: Echinodermata (sea stars, sea urchins)

• Shared characteristics define deuterostomes (Chordates and Echinoderms)

– Radial cleavage

– Formation of the mouth at the end of the embryo opposite the blastopore

• Echinoderms have a unique water vascular system, a network of hydraulic canals branching into tube feet that function in locomotion, feeding, and gas exchange

Phylum: Echinodermata

Phylum: Chordata (vertebrates)

• Phylum Chordata consists of two subphyla of invertebrates as well as hagfishes and vertebrates

• Vertebrates are a subphylum within the phylum Chordata

• Chordates are bilaterian animals that belong to the Deuterostomia.

• All chordates share a set of derived characters• Some species have some of these traits only during

embryonic development

Four key characteristics of chordates

– Notochord

– Dorsal, hollow nerve cord

– Pharyngeal slits or clefts

– Muscular, post-anal tail

EXAMPLES OF CORDATES