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This is a lecture presentation for my BIOL 201 Invertebrate Zoology students on Chapter 5: Porifera and Placozoa (Invertebrate Zoology, 7th Ed. by Ruppert, Fox, & Barnes, 2004). Rob Swatski, Assistant Professor of Biology, Harrisburg Area Community College - York Campus, York, PA. Email: [email protected] visit my website, BioGeekiWiki, for more biology learning resources: http://robswatskibiology.wetpaint.comVisit my Flickr photostream for anatomy model photographs! http://www.flickr.com/photos/rswatski/Thanks for looking!
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BIOL 201: Invertebrate Zoology
Chapter 5: Porifera & Placozoa
Rob SwatskiAsst. Prof. Biology
HACC-York1
Phylum Porifera
Porifera = the “pore-bearing” sponges
Not considered to be eumetazoans
Posses epithelioid & rudimentary
connective tissue
Lack true muscle & nervous tissues
2
PoriferaOverview
8000 species, most marine, 150 FW
Primitive, sessile filter feeders
Most asymmetrical, but some display radial symmetry
Erect, branching, or encrusting on
substratum3
Sponge Body Plans
Asconoid Syconoid Leuconoid
4
AsconoidSponges
Simplest body plan: hollow tube with base attached to
substrate
Ex: Leucosolenia
Have 1 large spongocoel (atrium) lined with 1 layer of
choanoderm
Choanocytes beat & draw water through
ostia (aquiferoussystem)
5
AsconoidSponges,
cont.
Water exits spongocoelthrough single large
osculum
Smallest & thinnest of all sponges (1 mm
diameter)
Growth imited by spongocoel diameter
If they had larger diameters, their body volume would exceed pumping capacity of
choanoderm6
SyconoidSponges
Body wall has incurrent canals & outpockets
(radial canals or choanocyte chambers) lined with choanoderm
Increases choanoderm SA & decreases spongocoel
volume
Larger than asconoidsponges (several cm), with
thicker body walls
Grantia & Sycon (Scypha)7
Syconoid sponge (Sycon)
8
LeuconoidSponges
Contains 1000’s of choanocyte chambers,
further increasing choanoderm SA
Smaller excurrent canals further reduce
spongocoel diameter
The largest sponges (several cm – 1+ m), with the thickest body walls; indeterminate growth
May have more than one osculum
9
Leuconoid sponge10
11
Structure of Sponge Body
Wall
Classified as either cellular or syncytial
Cellular spongeshave 2 primitive primary tissues:
epithelioid & mesohyl
Epithelioid tissue resembles epithelium
Mesohyl: middle CT layer of fibrous ECM
12
Epithelioid Tissue
Pinacoderm
Covers outer body & lines inner chambers (around
choanoderm)
Pinacoytes Porocytes
Choanoderm
Flagellated cells with a collar of microvilli
Choanocytes
13
14
Mesohyl Tissue(all cells are dynamic, totipotent & amoeboid)
Archeocytes
Can differentiate into any sponge cell; aide in digestion (phagocytosis)
& internal transport
Lophocytes
Secrete & maintain collagen fibers
Spongocytes
Produce thick skeletal spongin
fibers
15
16
Mesohyl Tissue, cont.
Sclerocytes
Secrete spicules: skeletal elements made
of silica or calcium
Myocytes
Muscle-like cells around osculum that constrict or dilate to control water flow
Germ cells
Reproductive cells: oocytes & spermatocytes
17
FW Leuconoidsponge
18
Syncytial Sponges
Contain simpler, reduced cells in a
syncytium, a continuous
cytoplasm that lacks membranes
No pinacoderm & choanoderm; have
collar bodies instead
Collar bodies are located
individually in collar body
chambers (not in epithelioid sheets)
Mesohyl with archeocytes,
sclerocytes, & germ cells
19
SyncytialSponges,
cont.
Body wall resembles 3-D
cobweb-like pattern: trabecular
syncytium
Each strand of the trabecular
syncytium encloses an axis of mesohyl
Contains collagen & spicules
20
Porifera Taxonomy
SP Symplasma(Hexactinellida)
Glass sponges: syncytial
Subphylum Cellularia(Cellular Sponges)
Class Demospongiae: 80% of all sponges; siliceous spicules &
spongin
Class Calcarea: calcareous
spicules
21
Glass Sponge(SP Symplasma)
22
SP Cellularia(Class Demospongiae)23
SP Cellularia(Class Calcarea)
24
SP Cellularia(Class Calcarea)
25
Sponge Skeleton
Diverse mesohyl acts as an endoskeleton
Some skeletons have fine collagen fibers
only
May contain spicules, spongin, or both
Incredible diversity of spicules: some project
through mesohyl to protect outer sponge
body26
27
28
29
Water Pumping
Most pump a water volume equal to their body volume every 5
seconds
Large SA & flow regulation slows down
velocity
Contract or relax myocytes to adjust osculum diameter
Can also close ostia & adjust flagellar beat of choanoderm & collar
bodies 30
31
32
Locomotion
Some have limited ability to move (1-4
mm per day)
Result of collective amoeboid movement of cells: very dynamic mesohyl environment
(remodeling)
Osculum contraction by myocytes
Whole body contraction
33
Nutrition
Filter feeders able to phagocytize food <
50µm (dinoflagellates, bacteria, viruses,
debris)
Some are carnivores & don’t filter; trap small
animals such as crustaceans
Choanocytes transfer particles to vacuoles
for digestion
Archeocytes remove wastes & inorganics
from system34
35
Symbiotic Relationships
Some have PSN endosymbionts: cyanobacteria, dinoflagellates,
chlorophytes
Symbionts help create the bright colors of
sponges
Sponges must live in shallow water for PSN
Some obtain up to 80% of nutrients from
photosynthate36
Internal Transport
Gas & waste transport via simple diffusion
Sponges are “leaky,” so water penetrates their
entire body
Sheets of cells are only 1 cell layer thick
Mobile amoeboid cells
37
Internal Transport,
cont.
Ammonia is the main metabolic waste
Common nitrogenous waste in aquatic
environments
Archeocytes transfer wastes & nutrients
Some individual cells posses contractile
vacuoles38
Nervous Tissue
Lack nerve cells
Some have localized action potentials responsible for
myocyte contraction
Glass sponges generate AP’s that
travel rapidly across their syncytium
Used to stop flagellar beating
39
Sponge Ecology
Many produce toxins to prevent
predation
Food for spongivores:
nudibranchs, fish, turtles
Hawksbill turtle feces can be up to
95% siliceous spicules!
Some release chemicals that kill
sessile competitors
(corals )40
41
42
Sponge Ecology,
cont.
Habitat for animals (shrimps & brittle
stars)
Decorator crabs place sponges on
their carapaces for defense & gliding
Cliona breaks down calcareous shells
Bores into shells for protection
43
44
Reproduction
Clonal reproduction via fragmentation &
budding
Sponges display incredible powers of
regeneration
Reproduce as a response to wave damage or grazing
Gemmules: spore-like masses of nutrient-
rich archeocytesenclosed by a shell; undergo diapause
45
Reproduction, cont.
Sponges frequently reproduce sexually
Hermaphrodites(monoecious)
Germ cells occurthroughout mesohyl
Choanocytes can also release sperm & form
eggs46
Reproduction, cont.
Sperm are broadcasted into water column
Choanocytesphagocytize incoming
sperm, but don’t digest them
Choanocytesdifferentiate into an
amoeboid cell & deliver sperm head to
egg
Most eggs fertilized via phagocytosis (most
sponge sperm lack an acrosome)
47
Reproduction, cont.
Some sponges are oviparous: release zygotes into water
column
Most are viviparous: retain zygotes within
body
Release larvae at a later period
Sponge larvae are very diverse:
coeloblastula, amphiblastula, parenchymella 48
49
Reproduction, cont.
Larvae are short-lived, settle in a few days, & creep across substrate
until suitable spot is found
Metamorphose into a juvenile
Varied lifespan: live several years in
temperate waters; 200+ years in tropics or
deep sea
Some only grow 0.2 mm/yr & could be
5000 years old with constant growth rate
50
Phylum Placozoa
Trichoplax: superficially resembles large ameba
(2-3 mm diameter)
Upper & lower cell layers, 25 µm thick
Enclosed by single layer of epithelioid cells
Densely ciliated ventral surface for locomotion
51
Phylum Placozoa, cont.
Fiber syncytium: CT layer of watery ECM &
syncytial network; contractile
Resembles ameba in form & locomotion as it glides across substratum
Feeds on algae via extracellular digestion
Reproduces asexually via budding &
fragmentation; sexual repro & larvae unknown
52
PlacozoanPhylogeny
Early evolutionary line of simple metazoans
Intermediate between sponges & cnidarians (RNA sequence data)
Resembles hypothetical protometazoan
Epithelioid layer is more similar to true epithelial
tissue53
54
Creditsby Rob Swatski, 2010
http://robswatskibiology.wetpaint.com
This work bears an Attribution-Noncommercial Share Alike Creative Commons license.
Visit my website for more Biology study resources!
http://www.flickr.com/photos/rswatski
Please send your comments and feedback to: [email protected]