05 chap 12 sponges and placozoa
TRANSCRIPT
Chapter 12
Mesozoaand
Parazoa
Fig 12-15
Origins of Metazoa
• Syncytical Hypothesis• Colonial Flagellate Hypothesis• Polyphyletic Origin
• Cells in these protists gradually became more specialized and layered
The animal kingdom probably originated from colonial protists
Figure 18.2Reece, campell,
mitchell
1 Early colony of protists;aggregate ofidentical cells
2 Hollow sphere(shown incross section)
3 Beginningof cellspecialization(cross section)
4 Infolding(cross section)
5 Gastrula-like“protoanimal”(cross section)
Digestivecavity
Reproductivecells
Somaticcells
Choanoflagellate Ancestors
• nucleic acids match• large colonies of choanoflagellates,
turned outside-in, wouldresemble sponges
small choanoflagellate colony
• Flagellated choanocytes filter food from the water passing through the porous body
Like hickman 12-5
Pores
WATERFLOW
Skeletalfiber
Centralcavity
Choanocyte
Amoebocyte
Choanocyte incontact withan amoebocyte
Flagella
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
larvae
Rhopalura
Fig 12-2
• Plate-like marine.• Asymmetrical, no organs or systems• Glides over food secreting enzymes
and absorbing products• Trichoplax adhaerens
Phylum Placozoa
Like figure 12-3
Phylum Placazoa
Dorsal epitheliumcover cells spheres
Ventral epitheliumciliated cellsgland cells
12.3
8. Porifera
Sponges, the SimplestAnimal Design
Choanocyte of a SpongeLike Hickman Fig. 12-10
Sponges Are Usually Asymmetricalcompare 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 Typeslike Hickman Fig. 12-10
Sponge Designs
compare HickmanFig. 12-5
SpiculesLike Hickman Fig. 12-11
• mineral needles• may be calcium car-
bonate 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
• Class Demospongiae– 95% species, siliceous spicules,
spongin,leuconoid canals
Venus flowerbasket
Spongilla
Ecology
• Habitat: freshwater or marine benthos– Sessile (= attached), often colorful
• Filter-feeders on suspended, microscopic organisms or detritus
Sponge Anatomy and Water Flowbased on Hickman Fig. 12-5
Cross section of sponge of intermediate complexity
spongocoel
incurrent canals
radial canal
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.