INTRODUCTION TO MARINE LIFE
1. PHYLUM PORIFERA
Porifera are sponges, some of the oldest fossil sponges date back to late Precambrian
era.
There are approximately 5 000 living species.
Sponges are composed of 3 distinct groups:
o Hexactinellida – glass sponges
o Demospongia – cartilaginous sponges
o Calcarea – calcareous sponges
South Africa has around 314 poriferan species.
Australia has 2426 species, mainly situation on the Great Barrier Reef.
Diagram showing cross-section of a poriferan
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,Characteristics
They are primarily marine – 150 species live in freshwater.
They have cellular-level organisation – cells are specialized with different cells
performing different functions.
They have a system of pores (ostia) & canals which water passes through.
Water movement is driven by beating of flagella – attached to choanocytes (collar cells).
Are radially symmetrical or asymmetrical.
Body Structure
Asconoid sponges = simple tube shape
Internal part is the spongocoel which contains the collar cells.
They have a single opening at the top called an Osculum.
Synconoid sponges = larger & have tubular body shape.
The body wall is thicker & pores are longer, forming system of simple canals – lined by
choanocytes.
Leuconoid sponges = largest & most complex
They consist of masses of tissue penetrated by numerous canals.
These canals lead to numerous chambers lined with choanocytes & flagella.
Water moves through canals, out via central canal & out osculum.
Class Calcera = most primitive & have all 3 as members.
Hexactinellida & Demospongiae = more complex & only have leuconoid members.
Asconoid Synconoid Leuconoid
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, Skeletal support
Sponges are supported by skeletons made up of protein (collagen) & spicules
Spicules can be calcareous, siliceous, or made of spongin.
Skeletal elements, choanocytes & other cells are embedded in gelatinous matrix = this is
called the mesophyll/mesoglea.
2. PHYLUM CNIDARIA
Characteristics
Bell-shaped/tubular animals
‘Cnidaria’ is derived from the term for stinging cells – cnidocytes.
Their body has layers:
o Outer protective epidermis
o Mesoglea
o Gastrodermis
o Inner endoderm layer – secretes juices and enzymes directly into gastrovascular
cavity (GVC).
They possess radial symmetry
Their mouth is surrounded by tentacles connected to GVC.
They have no circulatory, respiratory, or excretory organs.
Reproduction has two phases = sexual budding (polyps) and sexual reproduction
(medusa).
All are aquatic – mostly marine species.
They have 2 basic body forms during their life cycle:
o Polyps – mouth directed upwards, tubular/flower-like, sessile.
o Medusa – mouth directed downwards, jellyfish/umbrella shape, mobile.
Diagram showing the Polyp and Medusa
10
1. PHYLUM PORIFERA
Porifera are sponges, some of the oldest fossil sponges date back to late Precambrian
era.
There are approximately 5 000 living species.
Sponges are composed of 3 distinct groups:
o Hexactinellida – glass sponges
o Demospongia – cartilaginous sponges
o Calcarea – calcareous sponges
South Africa has around 314 poriferan species.
Australia has 2426 species, mainly situation on the Great Barrier Reef.
Diagram showing cross-section of a poriferan
8
,Characteristics
They are primarily marine – 150 species live in freshwater.
They have cellular-level organisation – cells are specialized with different cells
performing different functions.
They have a system of pores (ostia) & canals which water passes through.
Water movement is driven by beating of flagella – attached to choanocytes (collar cells).
Are radially symmetrical or asymmetrical.
Body Structure
Asconoid sponges = simple tube shape
Internal part is the spongocoel which contains the collar cells.
They have a single opening at the top called an Osculum.
Synconoid sponges = larger & have tubular body shape.
The body wall is thicker & pores are longer, forming system of simple canals – lined by
choanocytes.
Leuconoid sponges = largest & most complex
They consist of masses of tissue penetrated by numerous canals.
These canals lead to numerous chambers lined with choanocytes & flagella.
Water moves through canals, out via central canal & out osculum.
Class Calcera = most primitive & have all 3 as members.
Hexactinellida & Demospongiae = more complex & only have leuconoid members.
Asconoid Synconoid Leuconoid
9
, Skeletal support
Sponges are supported by skeletons made up of protein (collagen) & spicules
Spicules can be calcareous, siliceous, or made of spongin.
Skeletal elements, choanocytes & other cells are embedded in gelatinous matrix = this is
called the mesophyll/mesoglea.
2. PHYLUM CNIDARIA
Characteristics
Bell-shaped/tubular animals
‘Cnidaria’ is derived from the term for stinging cells – cnidocytes.
Their body has layers:
o Outer protective epidermis
o Mesoglea
o Gastrodermis
o Inner endoderm layer – secretes juices and enzymes directly into gastrovascular
cavity (GVC).
They possess radial symmetry
Their mouth is surrounded by tentacles connected to GVC.
They have no circulatory, respiratory, or excretory organs.
Reproduction has two phases = sexual budding (polyps) and sexual reproduction
(medusa).
All are aquatic – mostly marine species.
They have 2 basic body forms during their life cycle:
o Polyps – mouth directed upwards, tubular/flower-like, sessile.
o Medusa – mouth directed downwards, jellyfish/umbrella shape, mobile.
Diagram showing the Polyp and Medusa
10
