Phylum Porifera and Placozoa Flashcards
Porifera
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
Choanocytes
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
Mesohyle
Non-cellular gel layer (also called ‘mesenchyme’) located between the pinacoderm and the choanoderm, the cell layer that lines the spongocoel and contains choanocytes.
Spongocoel
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.
Ostia
Small pores that bring water into the sponge
Oscula
Large opening where water exits the sponge
Archaeocytes
(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
Spicules
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
Sclerocytes
Produce spicules
Develop from archaeocytes
Spongin
Collagenous protein produced by spongocytes
Develop from archaeocytes
Pinacoderm
Equivalent to the epidermis
Made of pinacocytes
Can contract and allow minor shape change
Asconoid sponges
Most simple sponge structure
Ostia formed by a single cell (a porocyte)
Sac with holes and central spongocoel
Syconoid sponges
Second most complex structure
Folds in the spongocoel form choanocyte chambers
Leuconoid sponges
Most complex structure
Folds within the folds in the spongocoel forming choanocyte chambers
Reduction of spongocoel
Ostia formed from several cells
Water flow in sponges
- rapid entry
- slow across choanocytes
- rapid exit
Gemmules
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
Class Calcarea
Marine
Calcium carbonate spicules
Contain all three sponge forms
Small percent of species
Class Demospongiae
Marine and freshwater
Silica and spongin spicules
Contain primarily leuconoid sponge forms (no asconoid)
>80% of sponge species
Class Hexactinellida
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
Sponge development
Hollow blastula (coeloblastula) inverts to form amphiblastula larva Larvae swim around and don’t feed
Sponge chemicals
Defensive function Useful in biomedical applications – respiratory – cardiovascular – gastrointestinal – antiinflammatory – antitumour – antibiotic Wound healing
Placozoa
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
