Chapter 8 : Inverterbrates

Noor Serina Binti Mohammad Shukor

Date of present:

1. Should be able to explain about animal’s origin.

2. List out animal’s general characteristic3. Describe the phyla of invertebrates, by

explaining and differentiating their characteristics besides discussing their life cycle.

Learning Objectives

Kingdom animalia

Animalia

Vertebrate(with backbone)

Invertebrate(no backbone)

1. Choanoflagellates • Group of protist that are suspension feeder

and posses collar cells2. Unicellular ciliates• Paramecium that posses two types of nucleus3. Spherical colonies• Volvox colony that mutates4. Placozoan• Is a plate-shaped, two layered animal with no

symmetry and no organs

Origin of animals

1. Animals are multicellular Cells are specialized to perform specific

function. 2. Animals are Heterotrophs get their raw materials and energy from

environment or other organisms 3. Animals are motile Heterotrophy often requires motility to

capture prey

8.1 General Characteristics

4. Animals reproduce sexually and in some cases asexually or both.

5. Animals have a period of embryonic development

embryonic development, cells become specialized and tissues form.

Diploid zygote undergoes cleavage, a series of mitotic division.

During cleavage, zygote divides and produce solid balls of cell. Result-> blastula

7. Animals can be classified according to body symmetry, type of body cavity.

Biologist divide animals into parazoa and eumatazoa.

Parazoa is multicellular organism having less specialized cell than in metazoa. Eg: Sponges

Eumatazoa consist of animals that have bodies differentiate into separates tissue, such as muscle, nerve tissue.

1. Symmetry i. Radial Symmetry ii. Bilateral Symmetry

iii. Assymmetry2. Tissue i. Ectoderm ii.Mesoderm iii.Endodem3. Body Cavity i. acoelomate ii. Pseudocoelom iii. Coelomates

Characterizing by ‘body plan’

Symmetry refers to the arrangement of body structures in relation to the axis of body.

Most animals exhibit either radial or bilateral symmetry

1. Symmetry

The body structures have generally formed of spherical or cylinder.

Multiple planes can be drawn through the central axis.

Animals with radial symmetry receive stimuli equally from all directions.

E.g. sea anemone, jellyfish, starfish.

i. Radial Symmetry

Sea Anemone Jelly Fish Star Fish

The body plan can be divided through only one plan which passes through the midline of the body.

It produces equivalent right and left halves that are mirror image.

Have a body axis passing from an anterior end (front) to a posterior end (back).

The body is separated into right and left sides along this main axis, and has a dorsal surface (backside) and ventral surface (underside

ii. Bilateral Symmetry

For animals with bilateral symmetry, there is an addition to their evolution, known as cephalization.

Cephalization• Is development of a head where sensory

structures are concentrated• As adaptions to locomotion

Body symmetry.  The flowerpot and shovel are included to help you remember the radial–bilateral distinction.

Have no pattern of symmetry Eg: sponges When body sponges cut into half, the two

halves are not mirror image/ not similar to one another.

iii. Assymetry

During the early development, most animals groups consist of three embryonic tissue layers, called germ layers.

Give rises to tissue.

Most animals are tripoblastic

2. Tissue

They posses three layers:• Ectoderm: The outer germ layer that gives rise

to the outer covering of the body and to the nervous system.

• Mesoderm: The middle layer that gives rise to most other body structures including muscles, skeletal structures and circulatory system

• Endoderm: The inner layer that forms the lining of digestive tube and other digestive organs.

Is a space that separates the digestive system and internal organ from the rest of the body.

3. Body cavity

Animal doest not have body cavity. Eg: flatworms (Phylum Platyhelminthes)

and proboscis worms (Phylum Nemertea)

i. Acoelomate(without cavity)

Animals have a body cavity but it does not develop from splitting of the mesoderm.

Eg: nematodes or roundworm or rotifer.

ii. Pseudocelomates (false coelom)

The body cavity is entirely lined with mesdoderm.

Eg: annelids

iii. Coelomate (true coelom)

8.2 Pattern of Development

Pattern in early development usually observed in coelomate animals.

There are 2 main evolutionary lines in coelomate animals that are:◦ protostomes (include mollusks, annelids and

arthropods)◦ deuterostomes (echinoderms and chordates)

Both are differ from each other due to the pattern of cleavage, developmental fate of the blastopore and formation of coelom.

A comparison of protostome and deuterostome development. 

How about this sponges?

Parazoa: Sponges (Phlum Porifera)

1.Class Calcarea2. Class Hexatinellida

3. Class Demosopngie

Porifera means ‘to have pores’ which bodies perforated by tiny holes.

Aquatic. Mostly marine with size range from 1 to 200cm in height.

Asymetrical animal but differ in shape from flat, encrusting growth to balls, cups fans, or vases

May be brightly colors. Some may live symbiotically with bacteria

or algae.

8.2 Phylum Porifera

They are believed to evolve from choanoflagellates

Sponges are multicellular In their life cycle, their larval

stages are able to swim but adult stage is sessile and attach to some solid object.

Several species have been observed to move slowly (±4mm per day).

A choanoflagellate colony. Such a colony is about 0.02 mm high. 

The sponge body is a sac with tiny openings through which water enters; a central cavity (spongocoel); and an open end, or osculum, through which water exits.

The outer layer is formed by epidermal cells. Meanwhile, the collar cells (choanocyte) make

up the inner layer, they create the water current and trap food.

Between the outer layer and inner layer cell is the mesohyl, contain amoeboid cells which is important in digestion and food transport.

Anatomy of a sponge. 

Sponges are suspension feeders, adapted for trapping and eating whatever food and water bring to them.

As water circulates through the body, the food is trapped along the sticky collars of chanocytes.

Foods are digested within the collar cells or transferred to ameboid cells for digestion and transport of nutrients to epidermal cells.

Undigested food passes out through the osculum and eliminated into the surrounding water.

There are 3 classes of sponges based on the type of skeleton they secrete:

• Class Calcarea: secretes a chalky skeleton composed of small CaCO3 spikes, or spicules.

• Class Hexactinella: the glass sponges with skeleton made of six-rayed spicules containing silica.

• Class Demospongiae: characterized by variable skeletons made of a fibrous protein material known as sponging or contains spicules of silica or combination of both. *Largest sponge classes ~95%

Yellow Calcareous Sponge

Gas exchanges and excretions of waste products depend on simple diffusion into and out of individual cells.

Sexual reproduction is simple because they are hermaphroditic, meaning that same individual can produce both eggs and sperms.

However, the production of egg and sperm are at different time in each individual and they cross-fertilize with other sponges.

Mature sperm are released into the water and are taken in by other sponges of the same species.

Fertilization and early development take place within the mesohyl. Embryo then move into the spongocoel and leave the parent by swimming, following the water flow.

When the larva find solid object, they attached and begin a sessile life.

Asexual reproduction is done by fragmentation. A small fragment break free from the parent and give rise to a new sponge.

Sponges can repair themselves to regenerate the lost parts. If the cells of a sponge are separated from one another, they can recognize each other and be reaggregated forming a complete sponge again.

8.3 Eumetazoa, Radial Symmetry

(Phylum Cnidaria)i. Class Hydrozoaii. Class Scypozoaiii. Class cubozoa

iv. Class anthozoa