Metazoa + Porifera

Question 1

What is a phylum?

Answer 1

A major group of animals thought to share a common evolutionary ancestor
Usually based on similarities in morphology/body-plan and/or similarities in development

Question 2

How many animal phyla are there?

Answer 2

There are 35 animal phyla
e.g. platyhelminths, arthropoda, mollusca

Question 3

How are evolutionary relationships of phyla identified?

Answer 3

Fossil record limited help
Usually based on anatomical similarities
Developmental/embryological similarities are more reliable

Question 4

What was the cambrian explosion?

Answer 4

About 540 mya, there was an explosion of animal diversity
The rocks contain a diverse range of fossils
Best documented early cambrian fauna is from the Burgess shale in Canada

Question 5

What is the Burgess Shale?

Answer 5

Best documented early cambrian fauna
First investigators (1909) expected to find primitive representatives of modern phylaso they placed them in known phyla

Question 6

What happened in the 1980’s in regards to the Burgess Shale?

Answer 6

Detailed examination found representatives of modern phyla but also unknown phyla, a much greater range of body plans

Question 7

What are the basic ways to separate phyla?

Answer 7

Symmetry
Grade body organisation
Body structure

Question 8

What are the evolutionary relationships of bilaterians?

Answer 8

Body cavity (coelom)- presence and arrangement (acoelomate, pseudocoelomate, and coelomates)

Protostomes (annelids, molluscs)
Deuterostomes (echinoderms, and chordates)

Question 9

What are the characteristics of the porifera?

Answer 9

• No true gut or tissues
• No true organs or nervous system
• Cells loosely aggregated, high regenerative potential
• Adults sessile, mostly marine
• Asymmetrical or radially symmetrical
• Water flow through pores, canals, chambers
• Chambers are lined with flagellated cells
• Possess internal skeleton of spicules

Question 10

What are the different grades of body structure in the porifera?

Answer 10

Asconoid- simplest body plan, single internal chamber called the spongocoel
Syconoid- Has a row of internal chambers called radial canals, which house choanocytes
Leuconoid- largest, multiple levels of radial canals

Question 11

What is the cellular organization of the porifera?

Answer 11

• Osculum
• Choanocyte
• Pinacocyte
• Spicule
• Prosopyte
• Amoebocyte
• Porocytes

Question 12

What does sponge feeding depend on?

Answer 12

On the surface area of choanocytes and this has to feed the body volume

Question 13

What are the different spicules?

Answer 13

Megascleres
Microscleres

Question 14

How are spicules arranged in the porifera?

Answer 14

Depends on the skeletal structure of the porifera:
- Simple skeletons- Spicules sparsely arranged for basic support
- Complex skeletons- spicules form frameworks
- Rigid skeletons- Spicules fuse into lattice like structures
Fibrous skeleton- Spicules embedded

Question 15

How do the porifera reproduce?

Answer 15

Both asexually and sexually

Question 16

How does asexual reproduction work in the porifera?

Answer 16

Budding: A new sponge grows from parent and detaches
Fragmentation: Pieces of the sponge break off and grow into new individuals
Gemmules: The resistant clusters of cells form in harsh conditions and develop into new sponges

Question 17

How do the porifera reproduce sexually?

Answer 17

Hermaphroditism: Most sponges produce both eggs and sperm but at different times

Fertilization: Sperm released into water captured by another sponges choanocytes, transported to eggs

Larval stage: Free swimming larva disperses to grow into new sponge

Question 18

What are the four classes of the porifera?

Answer 18

• Calcerea
• Hexactinellida
• Demispongiae
• Homoscleromorpha

Question 19

How is the class Calcerea described?

Answer 19

All grades of body organisation present
Mostly found in shallow marine environments
Spicules composed of calcium carbonate

Question 20

How is the class Hexactinellida described?

Answer 20

Glass sponges
Body organisation is generally syconoid
Mostly found in deep (450-900m) marine environments
Dominant sponges of Antarctic waters
Spicules composed of silica
Spicules include 6-pointed hexaxons that are often fused to form a lattice-like skeleton

Question 21

How is the class Demospongiae described?

Answer 21

Includes 95% of sponge species
Body organisation is leuconoid
Found in shallow and deep enviornments. Includes a few freshwater species
Skeleton may consist of spicules composed of silica or of ‘spongin’ fibers composed of protein or a combination of both

Question 22

How is the class Homoscleromorpha described?

Answer 22

Small number of species in 2 families
Separated from demosponges on the basis of molecular and morphological differences
Simple structure with spicules small or absent

Question 23

What are the growth forms of the porifera?

Answer 23

• Crustose and inconspicuous
• Giant vase or basket shaped sponges

Question 24

What are the oscula used for?

Answer 24

Oscula are often raised above surrounding surface which improves passive flow of water through the body of the sponge

Question 25

How does the oscula improve water flow through the sponge?

Answer 25

Water flowing over the surface of the sponge is accelerated as it is deflected up over the raised oscula
This causes a pressure drop and results in water being dragged out of the oscula thus helps to improve water flow

Question 26

How do sponges feed?

Answer 26

Sponges are extremely efficient filter feeders capable of processing large volumes of water and extracting particles as small as bacteria

Question 27

How does filter feeding work in sponges?

Answer 27

The flagellated choanocytes are capable of actively driving a flow of water through the sponge
Sponges thrive best in environments where fast currents assist by driving a flow of water through the sponge

Question 28

What can sponges build?

Answer 28

Well developed biogenic reefs