Metazoa + Porifera Flashcards
What is a phylum?
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
How many animal phyla are there?
There are 35 animal phyla
e.g. platyhelminths, arthropoda, mollusca
How are evolutionary relationships of phyla identified?
Fossil record limited help
Usually based on anatomical similarities
Developmental/embryological similarities are more reliable
What was the cambrian explosion?
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
What is the Burgess Shale?
Best documented early cambrian fauna
First investigators (1909) expected to find primitive representatives of modern phylaso they placed them in known phyla
What happened in the 1980’s in regards to the Burgess Shale?
Detailed examination found representatives of modern phyla but also unknown phyla, a much greater range of body plans
What are the basic ways to separate phyla?
Symmetry
Grade body organisation
Body structure
What are the evolutionary relationships of bilaterians?
Body cavity (coelom)- presence and arrangement (acoelomate, pseudocoelomate, and coelomates)
Protostomes (annelids, molluscs)
Deuterostomes (echinoderms, and chordates)
What are the characteristics of the porifera?
- 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
What are the different grades of body structure in the porifera?
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
What is the cellular organization of the porifera?
- Osculum
- Choanocyte
- Pinacocyte
- Spicule
- Prosopyte
- Amoebocyte
- Porocytes
What does sponge feeding depend on?
On the surface area of choanocytes and this has to feed the body volume
What are the different spicules?
Megascleres
Microscleres
How are spicules arranged in the porifera?
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
How do the porifera reproduce?
Both asexually and sexually
How does asexual reproduction work in the porifera?
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
How do the porifera reproduce sexually?
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
What are the four classes of the porifera?
- Calcerea
- Hexactinellida
- Demispongiae
- Homoscleromorpha
How is the class Calcerea described?
All grades of body organisation present
Mostly found in shallow marine environments
Spicules composed of calcium carbonate
How is the class Hexactinellida described?
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
How is the class Demospongiae described?
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
How is the class Homoscleromorpha described?
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
What are the growth forms of the porifera?
- Crustose and inconspicuous
- Giant vase or basket shaped sponges
What are the oscula used for?
Oscula are often raised above surrounding surface which improves passive flow of water through the body of the sponge
How does the oscula improve water flow through the sponge?
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
How do sponges feed?
Sponges are extremely efficient filter feeders capable of processing large volumes of water and extracting particles as small as bacteria
How does filter feeding work in sponges?
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
What can sponges build?
Well developed biogenic reefs
