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.