Learning Outcome

G2Phylum Porifera & Phylum Cnidaria

Learning Outcome G2 Analyse the increasing complexity of the

Phylum Porifera and the Phylum Cnidaria

Student Achievement Indicators

Students who have fully met this learning outcome will be able to:

Examine members of the Phylum Porifera and identify their unifying characteristics

Describe how poriferans carry out their life functions Examine members of the Phylum Cnidaria and identify their

unifying characteristics Describe how cnidarians carry out their life functions Compare polyp and medusa with respect to structure, general

function, and motility Suggest the advantages of a motile form in the life cycle of a

cnidarian Explain the evolutionary significance of colonial (poriferan)

versus multicellular (cnidarian) life forms Describe the ecological roles of sponges and cnidarians

Phylum Porifera – The Sponges

Classification Kingdom Animalia Phylum Porifera

Characteristics An invertebrate Sessile (do not move) Found in oceans and lakes Have specialized cells but these cells are

not arranged into organs or tissues No nervous system or brain No muscle tissue, which means sponges

are not capable of any type of movement

Characteristics Highly successful group; 500 million years

old An evolutionary dead end, because no other

groups have developed from the sponges Spicules make up the internal skeleton of

the sponges Amebocytes are specialized cells that build

spicules from calcium carbonate (CaCO3) or silicon dioxide (SiO2).

No body symmetry

Feeding Filter feeder Collar cells with flagellum create water

currents that brings water into and out of the cells

Water and food enter the sponge through small pores and exit via the osculum

Digestion occurs in the collar cells or amebocytes that wander around the middle layer of the sponge

ReproductionSexual Reproduction Generally hermaphroditic (produce both

male and female gametes) Have a motile larvae stage An egg (n) is fertilized by a sperm (n) and

develops into a free-swimming larvae (2n). Larve attaches to bottom undergoes

metamorphosis After metamorphosis an adults sponge

develops (2n)

ReproductionAsexual Reproduction Budding or branching Produces gemmules under unfavorable conditions Gemmules are sphere-shaped collections of

amebocytes surrounded by a tough layer of spicules.

These gemmules can survive long periods of freezing temperatures and droughts, which would kill an adult sponge.

When conditions become favorable again these gemmules will develop into a new adult sponge.

Ecological Roles Shelter for invertebrates Preyed on by bacteria, algae and other

microscopic organisms Form symbiotic relationships with

photosynthetic organisms. In this relationship the photosynthetic

organisms provide food and oxygen. The role of the sponge is to remove waste

Specialized amebocytes called “boring sponges” are vital in marine habitats because they clear the ocean floor

Protection Produce toxins and antibiotics that are

used to deter bacteria and algal predators

Human Uses Caribbean sponge has a compound that

may be useful in fighting leukemia and herpes

Phylum Cnidaria

Classification Kingdom Animalia Phylum Cnidaria

Class: Cubozoa (sea wasps or box jellyfish)

Class: Scyphozoa (jellyfishes) Class: Anthozoa (anemones and corals) Class: Hydrozoa (hydra)

Class Cubozoa

Class Scyphozoa

Class Anthozoa

Class Hydrozoa

Characteristics Invertebrate Radial symmetry Have true tissue, which allows specialization Only have two germ layers: ectoderm and endoderm Middle layer is not a mesoderm, but a layer composed of a

jelly-like substance called mesoglea. This group includes jellyfish, hydra, sea anemone and reef coral Aquatic organisms Generally marine, but there are fresh water species such as

hydra A nerve net encircles the body Some free swimming species have a ring of nerve cells around

the bell (perhaps a primitive beginning of a central nervous system)

Have coordination of nerves and muscles

Hydra

Feeding Capture food using specialized cells within the

tentacles called cnidocysts, which contains small sacs called nematocysts.

Nematocysts contain coiled, hollow tubes that shoot out rapidly and penetrates the skin of the prey

These nematocysts may contain toxins that paralyze the prey

Capture food and digest it in a sac-like cavity that has a single opening

Waste is expelled from the same opening This opening is controlled by muscle, which allows

cnidarians to engulf larger prey

Reproduction Alternation of generations lifecycle Two body forms: polyp and medusa

1. Polyp Has a sessile tube-like body within the

oral end directed upwards Vental end is attached to the ocean/lake

floor Example – hydra

Reproduction2. Medusa

Bell-shaped organism Mouth is located on the underside Have a thick middle layer called the

mesoglea Cnidarians are often known as

jellyfish due to their medusa state, although some species only have a polyp stage

Sexual Reproduction Egg/sperm arise from gastrodermal cells that have

migrated to specific locations in the epidermis of the polyp or on the underside of the medusa

Egg/sperm are released into the water and undergo external fertilization

Zygote develops into a free-swimming ciliated larva called a planula

Planula has an elongated body shape, is radially symmetrically, and has no gastrovascular cavity or mouth

Sexual Reproduction Planula attaches to substrate and develops

into a hydroid colony (polyp stage) Some hydroid colonies do not produce a

free swimming medusa stage Example – hydra Hydroid colonies exhibit specialization These colonies are used to facilitate

feeding and reproduction These colonies are also used as a defense

mechanisms.

Reproduction in Hydra Hydra may reproduce asexually Budding outgrowth of body walls Regeneration similar to sponges Hydra also reproduce sexually during

unfavorable conditions May be hermaphroditic or have separate sexes After fertilization zygote divides and becomes

an embryo that is enclosed in a protective case. This encased embryo is called a cyst, and it

drops of the parent and lies dormant until favorable conditions usually to spring.

Protection Used the same mechanisms as in feeding Specialized cells within the tentacle

called cnidocytes that can expel a poison that can be used to deter predators.

Ecological Roles Involved in symbiotic relationships with many

organisms Example - sea anemone and fish, shrimp and

small animals. These small organisms live among the tentacles of the very large sea anemone. The sea anemone protects the symbiont and provides food. In return the sea anemone is cleaned and protected by these symbionts from potential predators.

Also Provide habitats for many small invertebrates and microorganisms

Example - coral reefs

Human Uses Protect coasts areas from damage caused by storms and

large waves. These reefs are being damaged by pollution Once damaged the calcium carbonate skeleton of these

reefs break apart and no longer offer protection to our coastal areas

Coral is used to make beautiful jewelry and decorative articles

Corals produce certain chemical for their defense Some of these chemicals can be used to manufacture drugs

against cancer, and some toxins produced by corals are used by scientists to study and understand the function of nerve cells.