Phylum Porifera and Placozoa

Question 1

Porifera

Answer 1

A phylum of aquatic invertebrate animals that comprises the sponges. They are multicellular organisms that have bodies full of pores and channels allowing water to circulate through them, consisting of jelly-like mesohyl sandwiched between two thin layers of cells. Wikipedia

Question 2

Choanocytes

Answer 2

Flagellated cell with a collar of protoplasm at the base of the flagellum
Assist in food and sperm capture
Assist in water flow through the sponges

Question 3

Mesohyle

Answer 3

Non-cellular gel layer (also called ‘mesenchyme’) located between the pinacoderm and the choanoderm, the cell layer that lines the spongocoel and contains choanocytes.

Question 4

Spongocoel

Answer 4

Large, central cavity of sponges. Water enters the spongocoel through hundreds of tiny pores and exits through the larger opening. Depending on the body plan of the sponge, the spongocoel could be a simple interior space of the sponge or a complexly branched inner structure.

Question 5

Ostia

Answer 5

Small pores that bring water into the sponge

Question 6

Oscula

Answer 6

Large opening where water exits the sponge

Question 7

Archaeocytes

Answer 7

(Or amoebocytes) are amoeboid cells found in sponges.
Totipotent
Digest food extracellularly
Store food
Develop into sperm and egg
Aid in histocompatibility response
Specialize to secrete supporting elements in mesohyle

Question 8

Spicules

Answer 8

Small needle-like or sharp-pointed structures of calcium carbonate or silica which make up the skeleton of a sponge.
Produced by sclerocytes
Support and protection

Question 9

Sclerocytes

Answer 9

Produce spicules

Develop from archaeocytes

Question 10

Spongin

Answer 10

Collagenous protein produced by spongocytes

Develop from archaeocytes

Question 11

Pinacoderm

Answer 11

Equivalent to the epidermis
Made of pinacocytes
Can contract and allow minor shape change

Question 12

Asconoid sponges

Answer 12

Most simple sponge structure
Ostia formed by a single cell (a porocyte)
Sac with holes and central spongocoel

Question 13

Syconoid sponges

Answer 13

Second most complex structure

Folds in the spongocoel form choanocyte chambers

Question 14

Leuconoid sponges

Answer 14

Most complex structure
Folds within the folds in the spongocoel forming choanocyte chambers
Reduction of spongocoel
Ostia formed from several cells

Question 15

Water flow in sponges

Answer 15

• rapid entry
• slow across choanocytes
• rapid exit

Question 16

Gemmules

Answer 16

Packets of essential cells
• archaeocytes feed on other cells to get nutrients
• spongocytes surround archaeocytes - deposit Hard covering like spongin with embedded spicules
– resistant to:
• desiccation, low oxygen levels, low temperatures

Question 17

Class Calcarea

Answer 17

Marine
Calcium carbonate spicules
Contain all three sponge forms
Small percent of species

Question 18

Class Demospongiae

Answer 18

Marine and freshwater
Silica and spongin spicules
Contain primarily leuconoid sponge forms (no asconoid)
>80% of sponge species

Question 19

Class Hexactinellida

Answer 19

Glass sponges
6 rayed, silica spicules
Symmetrical skeleton
Outer layer a syncytium
• no pinacocytes, no pinacoderm, not contractile
Flagellated layer/chambers also syncytial
• contains flagella with collars
• all surfaces exposed to water covered by syncytial strands through which long spicules project

Question 20

Sponge development

Answer 20

Hollow blastula (coeloblastula) inverts to form amphiblastula larva
Larvae swim around and don’t feed

Question 21

Sponge chemicals

Answer 21

Defensive function
Useful in biomedical applications
– respiratory
– cardiovascular
– gastrointestinal
– antiinflammatory – antitumour
– antibiotic
Wound healing

Question 22

Placozoa

Answer 22

1 species: Trichoplax adhaerens 
Motile
Shallow marine and marine aquaria
2 layers of cells
• 1000 cells/layer 
• 4 cell types
Lower (ventral) layer
• columnar cells each with 1 flagellum 
• glandular cells
Upper layer
• thinner - flagellated cells, no glandular cells
Between - fluid-filled space with fibrous cells
That's it!
Disassociated cells reaggregate - like sponges