Chapter 12
Fig 12-15
Mesozoa
and
Parazoa
Origins of Metazoa
• Syncytical Hypothesis
• Colonial Flagellate Hypothesis
• Polyphyletic Origin
The animal kingdom probably
originated from colonial protists
• Cells in these protists gradually became
more specialized and layered
Digestive
cavity
Reproductive
cells
1 Early colony
of protists;
aggregate of
identical cells
2 Hollow sphere
(shown in
cross section)
Somatic
cells
3 Beginning
of cell
specialization
(cross section)
4
Infolding
(cross section)
5 Gastrula-like
“protoanimal”
(cross section)
Figure 18.2
Reece, campell,
mitchell
Choanoflagellate Ancestors
• nucleic acids match
• large colonies of choanoflagellates,
turned outside-in, would
resemble sponges
small choanoflagellate colony
• Flagellated choanocytes filter food from
the water passing through the porous
body
Choanocyte in
contact with
an amoebocyte
Pores
WATER
FLOW
Skeletal
fiber
Central
cavity
Choanocyte
Amoebocyte
Flagella
Like
hickman
12-5
Phylum Mesozoa
• Parasitic on marine invertebrates
• 20-30 cells arranged in two layers
– Classes
– Rhombozoans renal cephalopod parasite
– Orthonectida plasmodium like reproductive state
Phylum Mesozoa
Fig 12-2
larvae
Rhopalura
Phylum Placozoa
• Plate-like marine.
• Asymmetrical, no organs or systems
• Glides over food secreting enzymes
and absorbing products
Like figure 12-3
• Trichoplax adhaerens
Phylum Placazoa
Dorsal epithelium
cover cells
spheres
Ventral epithelium
ciliated cells
gland cells
12.3
8. Porifera
Sponges, the
Simplest
Animal
Design
Choanocyte of a Sponge
Like Hickman Fig. 12-10
Sponges Are Usually Asymmetrical
compare Hickman Fig. 12-15
Other Sponge Body Forms
Other Sponge Contrasts with
Eumetazoa
• Cellular level of organization
– no muscles or multicellular locomotion
– no nervous or digestive organs
• Unique skeletal structures
– proteinaceous spongin, mineral spicules
• Unique, cellular feeding process
Cellular Level of Organization
•
•
•
•
few kinds of cells (about 7)
dispersed cells reassemble on their own
cells don’t function together as tissues
no coordinated movements
– nerve and muscle cells absent
Start here!
Main Cell Types
like Hickman Fig. 12-10
Sponge
Designs
compare Hickman
Fig. 12-5
Spicules
Like Hickman Fig. 12-11
• mineral needles
• may be calcium carbonate or silica (glass)
• for skeletal support
and defense
Classification
• Kingdom Animalia
– Subkingdom Parazoa
– Phylum Porifera
– (means “pore-bearers”)
Porifora Taxonomy
• Class Calcarea
– Calcium carbonate spicules, 4
rayed
• Class Hexactinellida
– Siliceous six rayed spicules,
syconoid, leuconoid
Venus flower
basket
• Class Demospongiae
– 95% species, siliceous spicules,
spongin,leuconoid canals
Spongilla
Ecology
• Habitat: freshwater or marine
benthos
– Sessile (= attached), often colorful
• Filter-feeders on suspended,
microscopic organisms or detritus
Sponge Anatomy and Water Flow
based on Hickman Fig. 12-5
incurrent canals
spongocoel
radial canal
Cross section of sponge of intermediate complexity
Reproduction
• Sponges exchange sperm
• Zygotes develop in radial canals into
flagellated larvae
– Solid mass of cells, all same type
– Drift in the water and finally settle on
bottom
Reproduction
• Asexual by bud formation
– Regeneration after fragmentation
– Internal buds (gemmules)
• Archeacytes surounded by spongin and
spicules
– Tough Dormant Phase
– Mechanism to spread
Reproduction
• sexual
– Monoecious male and female in one
individual
•
•
•
•
•
A).Oocyetes develop from choanocytes
Sperm taken into the canal
B).both sperm an eggs expelled (oviparous)
Solid bodied parenchymula larva
Amphiblastula inversion
Sponges get respect!
The End.