Porifera Porifera The phylum Porifera (the sponges) includes The phylum Porifera (the sponges) includes about 5000 species almost all of which are about 5000 species almost all of which are marine (there are about 150 freshwater marine (there are about 150 freshwater species, members of the family Spongillidae). species, members of the family Spongillidae). Sponges occur worldwide at all latitudes from Sponges occur worldwide at all latitudes from the intertidal zone to the deep sea. the intertidal zone to the deep sea. Range in size from a few millimeters to 2 Range in size from a few millimeters to 2 meters across. meters across. Porifera means “pore-bearing” and refers to Porifera means “pore-bearing” and refers to the numerous pores and channels that permeate the numerous pores and channels that permeate a sponge’s body. a sponge’s body.
Transcript
PoriferaPorifera The phylum Porifera (the sponges) includes about 5000 The phylum Porifera (the sponges) includes about 5000
species almost all of which are marine (there are about species almost all of which are marine (there are about 150 freshwater species, members of the family 150 freshwater species, members of the family Spongillidae).Spongillidae).
Sponges occur worldwide at all latitudes from the Sponges occur worldwide at all latitudes from the intertidal zone to the deep sea.intertidal zone to the deep sea.
Range in size from a few millimeters to 2 meters across.Range in size from a few millimeters to 2 meters across.
Porifera means “pore-bearing” and refers to the Porifera means “pore-bearing” and refers to the numerous pores and channels that permeate a sponge’s numerous pores and channels that permeate a sponge’s body.body.
Barrel sponge
Yellow tube sponge
PoriferaPorifera
Sponges are the simplest multi-cellular Sponges are the simplest multi-cellular organisms, but they lack the germ layers organisms, but they lack the germ layers of more complex metazoans.of more complex metazoans. Have a cellular level of organization lacking Have a cellular level of organization lacking
true tissues and organs.true tissues and organs. Body is a mass of cells imbedded in a Body is a mass of cells imbedded in a
gelatinous matrix (mesohyl) which is gelatinous matrix (mesohyl) which is supported by a framework of spicules, as well supported by a framework of spicules, as well as collagen and spongin fibers.as collagen and spongin fibers.
Glass sponge spicules
6.8
Figure 12.06
Spicules form the stiffening skeletal structure of the sponge and may be made ofcalcium carbonate, silica or spongin [collagen].
Porifera feedingPorifera feeding
Sponges are sessile (they don’t move) and Sponges are sessile (they don’t move) and depend on water movement to bring in depend on water movement to bring in food and oxygen and remove wastes.food and oxygen and remove wastes.
Sponges generate their own flow of water Sponges generate their own flow of water having a unique water current system.having a unique water current system.
Porifera feedingPorifera feeding
Water enters through many small pores Water enters through many small pores called called ostiaostia and exits through fewer, and exits through fewer, larger larger osculaoscula. .
Oscula
Porifera feedingPorifera feeding
Openings are connected by a series of Openings are connected by a series of canals, which are lined by choanocytes canals, which are lined by choanocytes (the flagellated collar cells) that maintain (the flagellated collar cells) that maintain the current and filter out food particles.the current and filter out food particles.
Choanocytes
Porifera feedingPorifera feeding
The choanocyte’s collar consists of microvilli The choanocyte’s collar consists of microvilli joined together by delicate microfibrils,which joined together by delicate microfibrils,which filter out tiny food particles. filter out tiny food particles.
The beating of the flagellum draws water The beating of the flagellum draws water through the collar and out the top.through the collar and out the top.
Particles too big to pass through the collar get Particles too big to pass through the collar get trapped in mucus and slide down the collar to trapped in mucus and slide down the collar to the base where they are phagocytized.the base where they are phagocytized.
Figure 12.12c
Porifera feedingPorifera feeding
Sponges can filter enormous volumes of Sponges can filter enormous volumes of water as much as 20,000 times the water as much as 20,000 times the volume of the sponge in 24 hours.volume of the sponge in 24 hours.
Sponges mostly consume bacteria and Sponges mostly consume bacteria and may filter as much as 90% of those may filter as much as 90% of those passing through.passing through.
Carnivorous spongesCarnivorous sponges
A few sponges, however, capture small A few sponges, however, capture small prey, such as crustaceans.prey, such as crustaceans.
Members of the family Cladorhizidae Members of the family Cladorhizidae capture their prey using spicules that act capture their prey using spicules that act like velcro to hold the prey. Cells then like velcro to hold the prey. Cells then surround and digest the prey surround and digest the prey extracellularly.extracellularly.
Porifera feedingPorifera feeding
Some sponges also supplement their filter Some sponges also supplement their filter feeding by hosting symbionts such as feeding by hosting symbionts such as green algae, dinoflagellates or green algae, dinoflagellates or cyanobacteria that provide nutrients to the cyanobacteria that provide nutrients to the sponge.sponge.
Corals (which are Cnidarians not sponges) Corals (which are Cnidarians not sponges) similarly have symbiotic algae that live similarly have symbiotic algae that live with them.with them.
Types of cells in PoriferaTypes of cells in Porifera
Sponge cells occur scattered through a Sponge cells occur scattered through a gelatinous matrix called mesohyl. gelatinous matrix called mesohyl.
Spicules are distributed through the Spicules are distributed through the mesohyl as are several different mesohyl as are several different specialized cells types.specialized cells types.
Sponge cell typesSponge cell types
ArchaeocytesArchaeocytes: move around within the : move around within the mesohyl. They are ameboid in appearance and mesohyl. They are ameboid in appearance and carry out several tasks.carry out several tasks. Phagocytize particles and receive particles for Phagocytize particles and receive particles for
digestion from choanocytes.digestion from choanocytes. Can differentiate into other specialized cell types.Can differentiate into other specialized cell types. Secrete structural components. Specialized Secrete structural components. Specialized
archaeocytes called sclerocytes, spongocytes and archaeocytes called sclerocytes, spongocytes and collenocytes secrete respectively spicules, spongin collenocytes secrete respectively spicules, spongin and collagen.and collagen.
Sponge cell typesSponge cell types
ChoanocytesChoanocytes: (collar cells) engage in : (collar cells) engage in filter feeding. One end is imbedded in filter feeding. One end is imbedded in mesohyl and the other end protrudes.mesohyl and the other end protrudes.
The protruding end of the choanocyte has The protruding end of the choanocyte has a flagellum that moves water through a a flagellum that moves water through a mesh-like collar where small particles are mesh-like collar where small particles are trapped.trapped.
Sponge cell typesSponge cell types
PorocytesPorocytes: These are tubular cells that in : These are tubular cells that in the simplest type of sponge (asconoid the simplest type of sponge (asconoid sponges) form tubes through the wall of sponges) form tubes through the wall of the sponge and allow water to flow into the the sponge and allow water to flow into the central chamber.central chamber.
Sponge cell typesSponge cell types
Pinacocytes: Layers of pinacocytes form a flat, thin Pinacocytes: Layers of pinacocytes form a flat, thin epithelium-like layer (unlike true epithelium [a tissue] the epithelium-like layer (unlike true epithelium [a tissue] the individual cells are not joined by bands of extracellular individual cells are not joined by bands of extracellular proteins). proteins).
Pinacocytes cover exterior and some interior surfaces. Pinacocytes cover exterior and some interior surfaces.
Pinacocytes have some ability to contract and some are Pinacocytes have some ability to contract and some are arranged in bands around pores and use to regulate the arranged in bands around pores and use to regulate the flow of water in and out of the sponge.flow of water in and out of the sponge.
Canal systemsCanal systems
Most sponges have one of three types of Most sponges have one of three types of canal system:canal system: AsconoidAsconoid SyconoidSyconoid LeuconoidLeuconoid
These systems differ from in each other in These systems differ from in each other in the increasing complexity.the increasing complexity.
Canal systems: asconoidCanal systems: asconoid
Asconoid is the simplest system. Water Asconoid is the simplest system. Water enters through pores into a single large enters through pores into a single large central cavity (the spongocoel) which is central cavity (the spongocoel) which is lined with choanocytes. lined with choanocytes.
There is a single large osculum.There is a single large osculum.
Fig 6.3 a
Figure 12.07
Canal systems: syconoidCanal systems: syconoid
In syconoid canal systems there is still a In syconoid canal systems there is still a single spongocoel and osculum, but the single spongocoel and osculum, but the lining of the spongocoel is folded back to lining of the spongocoel is folded back to make radial canals lined with choanocytes.make radial canals lined with choanocytes.
6.3 b
6.5
Figure 12.09
Canal systems: leuconoidCanal systems: leuconoid
Leuconoid organization is most complex and Leuconoid organization is most complex and permits an increase in sponge size.permits an increase in sponge size.
Most leuconoids form large masses with Most leuconoids form large masses with numerous oscula.numerous oscula.
Clusters of choanocyte-lined chambers receive Clusters of choanocyte-lined chambers receive water from narrow incurrent canals and drive water from narrow incurrent canals and drive water into excurrent canals that eventually reach water into excurrent canals that eventually reach the osculum. There is no spongocoel.the osculum. There is no spongocoel.
6.3 c
Figure 12.07
Canal systemsCanal systems
The different grades of sponge canal complexity The different grades of sponge canal complexity do not imply an evolutionary sequence as the do not imply an evolutionary sequence as the leuconoid form has developed independently leuconoid form has developed independently numerous times within different classes of numerous times within different classes of sponges.sponges.
The leuconoid plan offers the significant The leuconoid plan offers the significant advantage of increasing the proportion of advantage of increasing the proportion of flagellated cells relative to total sponge volume.flagellated cells relative to total sponge volume.
Sponge reproductionSponge reproduction
Sponges reproduce both sexually and asexually.Sponges reproduce both sexually and asexually.
Most sexually reproducing species are Most sexually reproducing species are hermaphroditeshermaphrodites (individuals produce both male (individuals produce both male and female gametes at different times). and female gametes at different times).
Sperm are shed into the water and taken up by Sperm are shed into the water and taken up by other sponges. Individuals with eggs use special other sponges. Individuals with eggs use special cells called archaeocytes to transport sperm to cells called archaeocytes to transport sperm to the eggs.the eggs.
Sponge reproductionSponge reproduction
Zygotes develop into ciliated larvae that Zygotes develop into ciliated larvae that are released into the water and eventually are released into the water and eventually settle and develop into a sponge.settle and develop into a sponge.
Asexual reproduction is either by budding Asexual reproduction is either by budding or more commonly the production of or more commonly the production of gemmules which are clusters of cells gemmules which are clusters of cells surrounded by a protective coat.surrounded by a protective coat.
Figure 12.13
Gemmule
TotipotencyTotipotency
Sponge possess several different types of cells. Sponge possess several different types of cells. All sponge cells are totipotent and can give rise All sponge cells are totipotent and can give rise to any of the other types of cell.to any of the other types of cell.
A single cell can give rise to a new sponge or A single cell can give rise to a new sponge or can self-assemble with other cells into a sponge. can self-assemble with other cells into a sponge. (a sponge separated into its constituent cells will (a sponge separated into its constituent cells will spontaneously reassemble).spontaneously reassemble).
TotipotencyTotipotency
Individual cells hook on to other cells Individual cells hook on to other cells almost as if as Dawkins suggests (p484) almost as if as Dawkins suggests (p484) “they were autonomous protozoa with “they were autonomous protozoa with sociable tendencies.”sociable tendencies.”
Origins of multicellularityOrigins of multicellularity
Choanocytes the collar cells of sponges Choanocytes the collar cells of sponges bear a striking resemblance to free-living bear a striking resemblance to free-living unicellular choanoflagellates.unicellular choanoflagellates.
Choanoflagellate
Choanocytes
Choanoflagellates
Origins of multicellularityOrigins of multicellularity
There is general agreement that the origin of sponges There is general agreement that the origin of sponges and metazoans in general lies in a colony of flagellate and metazoans in general lies in a colony of flagellate protozoans.protozoans.
In one type of colonial choanoflagellate (Proterospongia) In one type of colonial choanoflagellate (Proterospongia) the individual cells are embedded in a gel matrix and the the individual cells are embedded in a gel matrix and the cells are almost indistinguishable from choanocytes.cells are almost indistinguishable from choanocytes.
Molecular evidence also supports the close relationship Molecular evidence also supports the close relationship between sponges and choanoflagellates.between sponges and choanoflagellates.
Groups of spongesGroups of sponges
There are three classes of sponges:There are three classes of sponges: Class CalcareaClass Calcarea Class HexactinellidaClass Hexactinellida Class DemospongiaeClass Demospongiae
CalcareaCalcarea
Calcareous sponges whose spicules are Calcareous sponges whose spicules are made of calcium carbonate. The spicules made of calcium carbonate. The spicules are straight or have 3 or 4 rays.are straight or have 3 or 4 rays.
Tend to be small (<10cm) and tubular or Tend to be small (<10cm) and tubular or vase shaped. vase shaped.
May be asconoid, syconoid or leuconoid in May be asconoid, syconoid or leuconoid in structure.structure.
Skeleton is made of six-rayed siliceous spicules Skeleton is made of six-rayed siliceous spicules bound in a glasslike lattice. Nearly all are deep sea bound in a glasslike lattice. Nearly all are deep sea forms.forms.
Body of hexactinellids consists of a single, syncytial Body of hexactinellids consists of a single, syncytial tissue (mass of protoplasm containing many nuclei, tissue (mass of protoplasm containing many nuclei, but not divided into cells). but not divided into cells).
This bilayered syncytium encloses a collagenous This bilayered syncytium encloses a collagenous mesohyl and various cells including choanoblasts mesohyl and various cells including choanoblasts which extend into the flagellated chamber through which extend into the flagellated chamber through openings in the reticulum.openings in the reticulum.
Figure 12.16
Figure 12.15
HexactinellidaCalcarea
DemospongiaeDemospongiae
The Demospongiae includes about 80% of all The Demospongiae includes about 80% of all species and includes the freshwater species and includes the freshwater Spongillidae. Spicules siliceous, spongin or both.Spongillidae. Spicules siliceous, spongin or both.
All members are leuconoid and most of the large All members are leuconoid and most of the large sponges are members of Demospongiae. sponges are members of Demospongiae. Loggerhead sponges may be a couple of meters Loggerhead sponges may be a couple of meters in diameter.in diameter.
Includes the bath sponges, which have only Includes the bath sponges, which have only spongin skeletons.spongin skeletons.
Figure 12.17a
Figure 12.17c
Marine Demospongiae on a Caribbean coral reef
Phylum PlacozoaPhylum Placozoa
Placozoans are tiny (<3mm), odd animals. Placozoans are tiny (<3mm), odd animals. Consist of a few thousand cells that form a Consist of a few thousand cells that form a flat transparent layer, but with ventral and flat transparent layer, but with ventral and dorsal sides that differ in structure.dorsal sides that differ in structure.
They feed by flowing over surfaces and They feed by flowing over surfaces and digesting small items they encounter.digesting small items they encounter.
Only 4 cell types occur in Placozoans (cf. Only 4 cell types occur in Placozoans (cf. 16-20 in sponges and >200 in mammals). 16-20 in sponges and >200 in mammals).
Nothing is known about Placozoan Nothing is known about Placozoan behavior in the wild. behavior in the wild.
They were discovered first in a European They were discovered first in a European aquarium in the 1880’s and have only aquarium in the 1880’s and have only been studied in the lab.been studied in the lab.
PlacozoansPlacozoans Because they are so simple, when these animals were Because they are so simple, when these animals were
first discovered it was thought they were the most first discovered it was thought they were the most primitive metazoans, even simpler than sponges.primitive metazoans, even simpler than sponges.
However, the dorsal surface of Placozoans is a tissue However, the dorsal surface of Placozoans is a tissue layer of ciliated cylinder cells and non-ciliated gland cells layer of ciliated cylinder cells and non-ciliated gland cells which suggests they diverged after the sponges which suggests they diverged after the sponges branched off from other animals. branched off from other animals.
There is some evidence that Placozoans may have There is some evidence that Placozoans may have diverged from other animals after the cnidarians diverged from other animals after the cnidarians (jellyfish) split off and secondarily became simplified, but (jellyfish) split off and secondarily became simplified, but the phylogenetic picture is still unresolved.the phylogenetic picture is still unresolved.
