||Zoology 250 (2017)
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) fully multicellular
b) ability to move (most species; unlike fungi and multicellular plants)
c) collagen (Type IV, found only in animals), a versatile glycoprotein (also occurs in plants & fungi but not as collagen) functions in many tissues (basal lamina, sponge mesohyl, most connective tissues)
d) heterotrophy- able to consume large-bodied organisms
- 2) PORIFERA (sponges) are sessile; approx. ~8000 marine, approx. ~200 freshwater spp.
- 3) Sponges are bizarre and clearly primitive animals: they show the least cellular differentiation and integration of all Metazoa; not considered true animals until 1765; even Haeckel (~1860) thought were protists!
- no true tissues (cellular level of organization), at least primitively
- 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 (in some, 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: many (small) incurrent pores (ostia), one or a few (large) excurrent pores (oscula), spacious spongocoel, and b) mesohyl - massive, mostly non-cellular, middle layer of spongin, spicules or both.
- 5) Sponge body plans vary 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 class Calcarea, but Demospongia have only the leucon type and Hexactinellida have a 'modified' leucon type
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Copyright (c) 2017 by A. Richard Palmer. All rights reserved.
(revised Dec. 19, 2016)