1. Biology 320 Invertebrate Zoology Fall 2005
Chapter 5 – Phylum Porifera

2. Phylum Porifera The sponges Name Porifera means “pore bearers”
First metazoan phylum we will discuss
Posses epithelioid and rudimentary connective tissue
Lack true muscle and nervous tissues
Not considered to be eumetazoans

3. Approximately 8000 spp. of sponges
Mostly marine, with approx. 150 described freshwater spp.
Primitive, sessile filter feeders
Most are asymmetrical, but some display radial symmetry
Can be erect, branching, or encrusting on substratum

4. Body Design
Three main forms of sponges, classified according to complexity
Asconoid
Syconoid
Leuconoid
Asconoid sponges
Simplest body plan
Resemble a hollow tube, with the base attached to the substrate
Possesses one large spongocoel lined with a single layer of choanoderm
Choanocytes beat and draw water through ostia in the epidermis

5. Asconoid sponges cont…
Water exits spongocoel through a single large osculum
Smallest of all sponges (1mm in diameter)
Thinnest body walls
Leucosolenia
Growth is limited by spongocoel diameter
If asconoid sponges had larger diameters, body volume would exceed pumping capacity of choanoderm
Therefore, a only a change in this simple body plan would permit the evolution of larger body sizes in sponges

7. Syconoid Sponges
Body wall contains pockets, known as choanocyte chambers, that are lined with choanoderm
Increases choanoderm surface area
Decreases spongocoel volume
Larger than asconoid sponges (one cm – a few cm)
Body walls are thicker than in asconoid sponges
Grantia and Sycon (formerly Scypha)

8. Leuconoid sponges
Contains thousands of choanocyte chambers, thereby further increasing the choanoderm SA
Spongocoel is further reduced
Therefore, these are the largest sponges (few cm to one meter, or more)
Thickest body walls
May possess more than one osculum

9. Body Wall Composition
The body walls of sponges are classified as either being cellular or syncytial
Cellular sponges have two primitive primary tissues
Epithelioid – resembles epithelium
Mesohyl – connective tissue middle layer
There are two specific types of epithelioid tissue
Pinacoderm – lines inside (except where choanoderm is present) and outside
Choanoderm – choanocytes posses a flagellum and collar of microvilli

11. All mesohyl cells are totipotent and amoeboid
Mesohyl is a fibrous (proteinaceous) ECM containing cells and skeletal elements
All mesohyl cells are totipotent and amoeboid
Archeocytes – can differentiate into any type of sponge cell. Aide in digestion (via phagocytosis) and internal transport
Lophocytes – secrete and maintain collagen fibers
Spongocytes – responsible for producing thick skeletal fibers known as spongin

12. Mesohyl cells cont…
Sclerocytes – secrete spicules, interesting skeletal elements made of silica or calcium
Myocytes – essentially muscle cells; usually concentrated around osculum. Constrict or dilate to control water flow
Germ cells – reproductive cells

13. Syncytial sponges DO posses cells, but not at the same level of organization as cellular sponges
Cytoplasm is continuous and lacks membranes that compartmentalize separate cells
Lack pinacoderm
Lack choanoderm. Posses collar bodies instead; these are located in collar body chambers, individually rather than in epitheliod sheets
Mesohyl is present and contains archeocytes, sclerocytes, and germ cells

14. Syncytial sponges cont…
Body wall resembles a 3D cobweb-like pattern and is called a trabecular syncytium
Each strand of the trabecular syncytium encloses an axis of mesohyl
Collagen and spicules are present

15. Taxonomy
Two subphyla
Subphylum Symplasma (Hexactinellida)
Subphylum Cellularia
Subphylum Symplasma consists of glass sponges that posses syncytial tissues
Most sponges belong to Subphylum Cellularia, which is divided into two main classes, both possessing cellular tissues
Class Demospongiae – have siliceous spicules and spongin
Class Calcarea – have calcareous spicules

16. Skeleton Any cell, organism, etc. needs some form of support
Mesohyl acts as an endoskeleton
Diversity of mesohylar structure
Fine collagen fibers only
May be supplemented with spicules, spongin, or both
Incredible diversity of spicules; and some can project through mesohyl to protect the outside of the sponge

18. Water Pumping
Most pump a volume of water equal to their body volume, every 5 seconds
Can slow / stop water flow to avoid taking in silt
Can control rate of water flow via
Contracting or relaxing myocytes, which controls osculum diameter
Closing ostia
Adjusting flagellar beat of choanoderm / collar bodies

19. Locomotion Some have limited capacity for locomotion
Can move 1 to 4 mm per day
Result of collected amoeboid movement of cells
Osculum contraction
Whole body contraction

20. Nutrition Filter feeders
Typically phagocytize particles of 50µm or less
Particle size determines which cells phagocytize
All cells can phagocytize
Choanocytes transfer particles to vacuoles for digestion
Archeocytes remove wastes / inorganics from system

21. Feed on dinoflagellates, bacteria, viruses, debris, etc.
Some are carnivorous (don’t filter); trap small animals such as crustaceans

22. May posses photosynthetic endosymbionts
Cyanobacteria
Dinoflagellates
Chlorophytes
Symbionts may cause sponge to be brightly colored
Sponges must live in shallow water to photosynthesize
Some obtain up to 80% of nutrients from photosynthate

23. Internal Transport
Gas / waste transport is carried out via simple diffusion
Sponges are “leaky,” so water penetrates almost the entire animal
Sheets of cells are only one cell layer thick
Mobile amoeboid cells
Ammonia is the main metabolic waste
Almost always the case for animals in aqueous environments
Uric acid or urea in terrestrial habitats
Archeocytes transfer wastes / nutrients
Some individual cells posses contractile vacuoles

24. Nervous Tissue Lack nerve cells
Some have localized impulses responsible for myocyte contraction
Glass sponges can generate action potentials that travel all across their syncytium at a rapid rate
Used to arrest flagellar beating

25. Ecology Many produce toxins to prevent predation
Some animals are spongivores
Nudibranchs
Fish
Turtles – Hawksbill turtle feces can be up to 95% siliceous spicules
Some release chemicals that kill competing sessile organisms, such as corals

26. Some animals such as shrimps and brittle stars live in sponges
Decorator crabs may place sponges on their carapaces
Cliona breaks down calcareous shells. Bores into shells for protection

27. Reproduction Sponges are excellent regenerators
Reproduce clonally through several methods
Fragmentation – usually due to wave damage or grazing
Budding
Gemmules (winter bodies) – spore-like structures that are essentially a mass of nutrient-laden archeocytes that are surrounded by a shell. Undergo diapause

29. Sponges frequently reproduce sexually
Sponges are hermaphrodites (monoecious)
Germ cells occur throughout mesohyl
Choanocytes can also release sperm, and form eggs

30. Sperm are broadcasted into water column
Choanocytes phagocytize incoming sperm, but don’t digest
They differentiate into an amoeboid cell and deliver sperm head to egg
Most eggs are fertilized through phagocytosis (therefore, most sponge sperm lack an acrosome)

31. Some sponges are oviparous, and release zygotes into water column
Most are viviparous, and retain zygotes in their body, later releasing larvae
Sponge larvae are very diverse

32. Larvae are short lived Varied lifespans Settle within a few days
Creep across substrate until a suitable spot is found
Metamorphose into a juvenile
Varied lifespans
May live one to a few years in temperate zones
Tropical or deep sea spp. May live 200 years or more
Some only grow 0.2 mm/yr, and could be 5000 years old if that growth rate is constant