Phylum Porifera and Phylum Placozoa Chapter 12 Flashcards
What are choanoflagellates and discuss the importance of choanoflagellates in
understanding hypotheses multicellular animals.
- Choanoflagellates are solitary or colonial aquatic eukaryotes, with each cell carrying a flagellum surrounded by a collar of tentacles. Beating of the flagellum draws water into the collar, where tentacles collect tiny particles, typically bacteria.
- Choanoflagellate cells are noteworthy because they strongly resemble sponge feeding cells called choanocytes (see Section 12.2). It is very interesting to find a collared cell used in filter-feeding in a colonial eukaryote and in a sponge, the sister taxon of all other animals (see the Cladogram of All Animal Phyla on inside front cover
12.2 What are the synapomorphies that define Phylum Porifera?
Synapomorphies:
- Cellular level of organization (no tissues)
- Possess Choanocytes
- Internal system of pores and canals
12.3 Describe the basic features of sponges in terms of their grade of organization and body
symmetry
No body symmetry (sometimes radial)
* Sessile (don’t move)
- Skeleton: spicules in a fibrous
network of spongin (collagen) - Ostium (pl. ostia) = incurrent
opening (small pores) - Osculum = excurrent opening
(larger) - 3 types of canal systems:
– Asconoid: simplest; choanocytes
line spongocoel
– Syconoid; body wall folded;
choanocytes line radial canals
– Leuconoid; most complex;
choanocytes line internal chambers;
2.4 How are the following classes of sponges distinguished?
Class Calcipongiae (aka Calcarea)
Class Hexactinellida (Hyalophongiae)
Class Demospongiae
-Class Calcipongiae (aka Calcarea) -calcium carbonate spicules
- Class Hexactinellida (Hyalophongiae) - 6-rayed silaceous spicules
- Class Demospongiae- Silaceous spicules not 6-rayed; may be absent
12.5 Describe how sponges acquire and digest food.
Sponges are suspension feeders
* Choanocyte – flagellated “collar cell”
– Flagella beats; pulls water in through ostia
– ‘collar’ of microfibrils traps particles
– choanocytes phagocytize particles & pass them to achaeocytes for digestion
– Digestive system is intracellular
12.6 Describe the three types of canal systems in sponges:
Asconoid
Syconoid
Leuconoid
3 types of canal systems:
– Asconoid: simplest; choanocytes
line spongocoel
– Syconoid; body wall folded;
choanocytes line radial canals
– Leuconoid; most complex;
choanocytes line internal chambers
12.7 Describe the function of each cell type in a sponge:
Pinacocyte
Archaeocytes
Sclerocytes
Spongocytes
Collenocytes
Choanocytes
Mesohyl
- Mesohyl = extracellular gelatinous matrix
- Pinacocytes = outer layer (called Pinacoderm)
– Can ingest food particles (phagocytosis)
– Some contractile (myocytes); especially around ostia or oscula
– Not a true tissue (no basal lamina) - Archaeocytes
– ameboid cells; phagocytize particles esp. particles for digestion
– Differentiate into other types of cells - sclerocytes – secrete spicules
- spongocytes secrete spongin
- Collencytes secrete collagen
- Choanocytes
– Flagellated; create current flow
12.8 Describe asexual reproduction in sponges via fragmentation, budding, and gemmules
Asexual
– Fragmentation (somatic embryogenesis)
– Budding (external buds)
– Gemmules (internal buds; mostly FW sponges)
12.9 Describe the basic method of sexual reproduction in most sponges
Sexual: Most monoecious (have both male & female sex cells)
– Gametes arise from choanocytes (archaeocytes in some)
* Most sponges: sperm released; phagocytized by archeocytes carried to oocytes; parent
releases ciliated larva (parenchymula)
* In others: Egg & sperm released, form parenchymula
12.10 What is a parenchymula?
Most sponges: sperm released; phagocytized by archeocytes carried to oocytes; parent
releases ciliated larva (parenchymula)
* In others: Egg & sperm released, form parenchymula
-The free-swimming larva of most sponges is a solid-bodied parenchymula (see Figure 12.12A), although six other larval types exist, and some sponges exhibit direct development.
