• 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
• 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
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
SpiculesLike Hickman Fig. 12-11
• mineral needles• may be calcium car-
bonate or silica (glass)• for skeletal support
and defense
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