Z250 - Lec6 Outline. Porifera I (2009)

Zoology 250 (2009)

INTRO. TO METAZOA;
Phylum PORIFERA I: General Features

(Porifera study images;
click on tree to see full cladogram)

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1) METAZOA=ANIMALIA. Key traits permitted amazing diversity:
a) multicellularity
b) ability to move (most species; unlike fungi and multicellular plants)
c) collagen (found only in animals), a versatile glycoprotein that functions in many tissues (basal lamina, sponge mesohyl, most connective tissues)
d) heterotrophy- able to consume large-bodied plants and other animals
2) PORIFERA (sponges) are sessile; approx. ~8000 marine, approx. ~200 freshwater spp.
3) Sponges are bizarre and clearly primitive; they show the least cellular differentiation & integration of all Metazoa (not considered true animals until 1765)
- no true tissues (cellular level of organization)
- no mouth or gut!
- no muscles or reproductive, digestive, respiratory, sensory or excretory organs (no organs at all!)
- no circulatory system even though they reach quite large size
- cells are remarkably autonomous (disassociated cells transform into amoebocytes & re-aggregate to form a new sponge!)
- many show no clear axes of symmetry (some superficially radial)
- so different from other Metazoa they are sometimes put in separate sub-kingdom Parazoa (other animals in Eumetazoa)
4) Defining sponge traits include: a) water-canal system (= aquiferous system) includes: many (small) incurrent pores (ostia), one or a few (large) excurrent pores (oscula), spacious spongocoel, and b) mesohyl - massive, mostly non-cellular middle layer.
5) Colony form varies from simple to complex
- ascon type- single flagellated pumping cavity (spongocoel)
- sycon type- many flagellated canals radiate from spongocoel
- leucon type- many flagellated chambers connect by passive canals
- all 3 occur in Calcarea, but Demospongia have only the leucon type

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