Chapter 12: Sponges and Placozoans

What is an advantage of being multicellular?

low surface to volume ratio

What are the first multicellular animals?

sponges

Sponge cells are embedded in

an extracellular matrix

When are sponges recognized as animals/plants?

19th century

Sponges are sister to

choanoflagellate algae

What do choanoflagellates and sponges both possess

choanocyte cells

Are organisms with choanocytes sessile or mobile?

sessile

Evidence FOR common animals colonial

“prototype” multicellular organism

similar cell communication mechanisms

Evidence AGAINST common animals colonial

choanocytes only in adult sponges

not seen in other phylogenetic groups

Porifera means

porus (pore) and fera (bearing)

Sponge size

2 mm to 2 mm

Phylum Porifera is unicellular or multicellular?

multicellular

Phylum Porifera possess pores that

facilitate water movement

Phylum Porifera has bilaterial symmetry or radial symmetry?

radial

What are the only animals with no organs or true tissues?

sponges

What type of digestion do sponges have?

intracellular

Do sponges have a nervous system?

very limited

Sponges reproduce asexually by

buds/gemmules or somatic embryogenesis

Sponges reproduce sexually by

monoecious, parenchymula, cross or self fertilize

What are embedded in spongin for support

spicules

Pinacoderm

incurrent pores on cells (protective)

Dermal ostia

incurrent pores for the sponge (water)

What does it mean when a sponge is a suspension feeder

phagocytosis for larger particles

pinocytosis for smaller proteins

Mesohyl (mesenchyme)

gelatinous extracellular matrix

Archaeocytes

ameboid cells that move in the mesohyl

Sclerocytes, spongocytes, collencytes, and lophocytes are different types of

archeocytes

Sclerocytes make

spicules

Spongocytes make

spongin

Collencytes and lophocytes make

collagen

What are the closest thing a sponge has to true tissues?

pinacocytes

Myocytes

regulate water flow through contraction

What are the three body forms

asconoid, syconoid, and leuconoid

What puts the flagellated cells on the outside for swimming in Calcarea?

blastula develops and turns outward (inversion)

Asexual reproduction mode advantages

no gene dilution, good for stable environments, all individuals can reproduce

Asexual reproduction mode disadvantages

less dispersal, reduced adaptability, risk of accumulating mutations

Muller’s ratchet

Mutcher’s rachet

negative mutations over time

Sexual reproduction mode advantages

genetic variation, better dispersal

Sexual reproduction mode disadvantages

energy-intensive, requires mates, offspring more fragile

What are the classes of Phylum Porifera?

Calcarea, Hexactinellida, Demospongiae

Class Calcarea

calcium carbonate spicules

Class Hexactinellida

glass sponges

Class Demospongiae

siliceous, but not six rayed

Which class has all three sponge forms

Calcarea

Which class is typically small and vase shaped

Calcarea

Which class is vase or funnel shaped

Hexactinellida

Syncytial cell structure

many nuclei in a single cell

cellular respiration without cytokinesis

Which class has syncytial cell structure?

Hexactinellida

Which class has all shapes but is only leuconoid?

Demospongiae

Which class are freshwater sponges in?

Demospongiae

Placozoa roots

plakos (tablet) and zoon (animal)

Phylum Placozoa contains how many species?

one

How does Phylum Placozoa reproduce?

asexually by budding and fusion

Scavengers

glide over food, secrete digestive enzymes, absorb the products

The only species in Phylum Placozoa is

Trichoplax adhaerens

Somatic embryogenesis

regeneration from fragments