Life science is interesting

1. Multicellular and
Chapter 9
Tissue Levels of
Organization

2. Origins of Multicellularity
• Multicellular life arose quickly in the
100 million years prior to
Precambrian/ Cambrian boundary
• The evolutionary events that leads
to multicellularity is a mystery
• Scientist believe that multicellularity
could have arisen as dividing cells
remained together.
called COLONIAL HYPOTHESIS
(hypothesis)

4. • Second hypothesis –
SYNCYTIAL HYPOTHESIS
- a syncytium is a large,
multinucleated cell. The formation of
plasma membranes in the cytoplasm
of a syncytial protist, could have
produced a small, multicellular
organism

5. (Syncytial refers to protoplasm
that contains numerous nuclei
not separated from each other
by plasma membrane).
Problems with Syncytial Theory
• Radial symmetry occurs in
"Radiates" (sponges,
cnidarians, ctenophores, and
placozoans)
• No evidence of syncytial cells
in basal metazoans.

6. Phylum Porifera - Sponges
• Primarily marine animals that consist
of loosely organized cells; approx 9k
spp, from < 1cm to > 1m

7. Characteristics of members
of Phylum Porifera include:
1. asymmetrical or radial symmetry
2. 3 types of cells - pinacocytes,
mesenchyme cells (amoebocytes) and
choanocytes
3. Central cavity or several branching
chambers, thru which water flows for filter
feeding
4. no tissues or organs

8. Cell types, Body wall, and
Skeletons
1. sponge cells are specialized for particular
functions (division of labor)
a. Pinacocytes
= These cells are the "skin cells" of
sponges. They line the exterior of the
sponge body wall. They are thin, leathery
and tightly packed together.
= may be slightly contractile and help
sponge change shape.
= Some pinacocytes specialized into
porocytes, which regulate water circulation

10. • b. jelly like layer under pinacocytes is
termed mesohyl. Mesenchyme cells are
amoeboid, and move about in the mesohyl.
Specialized for reproduction, transporting
and storing food, secreting skeletal
elements (spicules)
c. beneath mesenchyme, lining inner
chambers are choanocytes - collar cells.
Flagellated cells with ring of microvilli
surrounding flagella. Microfilaments
connect microvilli, forming a net that helps
filter edible particles

12. Sponges are supported by
skeleton that may consist of
spicules - needlelike spikes
• spicules are formed by amoeboid cells
• made of CaCO3 or silica
• may take on a variety of shapes
• alternatively, skeleton may be made of
spongin, a fibrous protein made of
collagen - dried beaten and washed to
produce commercial sponges

13. Spicules

14. Types of spicules

17. Water currents and body
forms
• sponges lives depend on the water
currents that choanocytes create
1. water brings food and O2,
removes wastes
2. methods of food filtration and
circulation reflect body forms in the
phylum

19. Three types of body
forms:
• a. ascon body form - simplest and
least common. Vaselike form
»ostia are outer openings of
porocytes and lead directly to
chamber called spongocoel
»choanocytes line spongocoel
and their flagellar movements
draw water into the spongocoel
thru the ostia
»water exits sponge thru
osculum, single large opening at
the top of the sponge

22. b. sycon body form - sponge
wall appears folded
• water enters thru dermal pores,
which are openings of incurrent
canals
• pores in body walls open to radial
canals, and radial canals lead to
spongocoel
• choanocytes line radial canals and
beating of flagella moves water from
ostia, thru incurrent and radial
canals, to spongocoel and out the
osculum.

24. c. leucon body forms have an
extensively branched canal
system.
• Water enters the ostium and moves thru
branched incurrent canals,
• incurrent canals lead to choanocyte lined
chambers. Canals leading away from the
chambers are called excurrent canals
• proliferation of chambers and canals has
resulted in absence of spongocoel. Often
there are multiple exit points for water
leaving sponge

26. Maintenance functions
1. sponges feed on particles that range in
size from .1 to 50 um.
a. bacteria
b. microscopic algae
c. protists
d. other suspended particles
2. important in reducing coastal turbidity
a. 1 leucon sponge, 1 cm in diameter and
10 cm high, filters 20 liters of water/day!

27. 3. a few sponges are carnivorous - catch
small crustaceans (deep water) with
spicule-covered filaments.
4. feeding methods - choanocytes filter small
suspended particles.
• a. Water passes thru collar near base and
moves into spongocoel at open end of
collar
• b. suspended food is trapped on collar
and moved along microvilli to base of
collar, where it is incorporated into a
food vacuole

28. • c. lysozymal enzymes and pH
changes digest particle in vacuole
• partly digested food passed to
amoeboid cells, that distribute it
• pinacocytes lining incurrent canals
may phagocytize larger food
particles. Sponges may also absorb
nutrients in sea water thru active
transport

29. Feeding – filter feeding

30. 5. Sponges get rid of waste thru
diffusion, since all cells are in close
contact with water
6. Sponges have no nerve cells for
communication/coordination, but
somehow choanocytes can cease
activities more or less
simultaneously, ceasing water
circulation. chemical messages sent
by ameboid cells is one possible
method

31. Reproduction
• most sponges are monoecious - both
sexes occur in same individual; do
not usually self fertilize because eggs
and sperm ready at different times.
• Asexual. buds or, in many freshwater
species, gemmules

32. • Development usually internal.
• Larvae free-swimming, and come in a
variety of forms.

33. • 1. certain choanocytes lose collars and
flagella and undergo meiosis to form
flagellated sperm
2. other choanocytes may undergo
meiosis and form eggs. Eggs retained in
mesohyl of parent
• 3. sperm cells exit one sponge by osculum
and enter another with incurrent water.
they are trapped by choanocytes and put
in vacuoles.
• 4.sperm lose collar and flagella, become
ameboid and transfer sperm to eggs

34. • 5. early development occurs in mesohyl,
then a flagellated larva forms. Larva breaks
free, free-swims for up to 2 days before
settling to substrate and develops into
adult form (Fig. 9.8)
• 6.some sponges form resistant capsules
called gemmules, which contain masses of
ameboid cells. gemmules can survive
freezing and drying (9.8c,d) When
favorable conditions return, ameboid cells
stream out of tiny opening, and organize
into a sponge
• 7. Some sponges can regenerate from an
individual cut or broken apart.

35. Classes of Porifera
• Hexactinellida glass sponges, siliceous
lattice, syconoid forms
• Spicules – hexaxons
• Lattice – siliceous w/ sieve plate over
osculum
• Basal spicules w/ tufts for soft sediment
• Structure and habitat
• Individualized cup, urns or vase shape
• Body wall- w/out pinacoderm, syncitium
externally and internally
• Deep water (200 meters-abyss) /
Cosmopolitan w/ more in Antarctic

36. Euplectella

38. Class Calcarea
(Calcispongeae)
• Spicules - Mon-, tri-, or tetraxon
shapes
• Calcium carbonate, No spongin
• Structure and habitat
• Small (<10 cm)
• Occupy shallow water
• Cosmopolitan
• All 3 body types

39. Leucosolenia

40. Class Demospongiae
• – most common form, leuconoid
forms
• Spicules - Tri- or tetraxon
• Along with spongin
• Structure and habitat
• Brightly colored (amebocytes w/
pigment)
• Shape reflects habitat & resources
available
• Encrusting on vertical surfaces or in
crevices

41. • Tubular (w/ branching) on limited
substrates (conserves space)
• Shallow to deep water
• Algal symbionts- non-motile
zooxanthella or cyanobacters in
mesohyl or amebocytes

42. Grass sponge

43. Class Sclerospongiae
• – Leuconoid forms, Found in grottos
or coral tunnels
• Internal siliceous spicules & spngin
• External calcareous portion

44. The End