| Zoology 250 (2002) INTRO. TO METAZOA; Phylum PORIFERA I (Porifera study images; click on tree to see full cladogram) |
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- 1) Metazoa=Animalia: capable of movement (most, contrasts with fungi and multicellular plants), heterotrophic, truly multicellular; pass through a blastula stage; possess collagen
- 2) Porifera (sponges) are sessile; ~5000 marine, ~150 freshwater spp.
- 3) Sponges are bizarre & 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 true endoderm (i.e., 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 differerent from other Metazoa they are sometimes put in separate sub-kingdom Parazoa (other animals in Eumetazoa)
- 4) Three classes of Porifera to note (a fourth class is not covered):
- CALCARAE: calcareous spicules, lack spongin, small: <15cm
- DEMOSPONGIAE: silica spicules, with spongin in some; most successful group of sponges; can be large: >2m
- HEXACTINELLIDA: "glass sponges"; silica spicules, lack spongin; an odd, mostly deep sea taxon; can be large: 10 - 50cm; body formed of syncytial sheets, even choanocytes lack nuclei!
- 5) Water-canal system includes: many (small) incurrent pores (ostia), one or a few (large) excurrent pores (oscula), spacious spongocoel.
- 6) Colony form varies from simple to complex
- ascon type- single flagellated pumping cavity (spongocoel)
- sycon type- many flagellated pumping canals radiate from spongocoel
- leucon type- many flagellated chambers connect by passive canals
- all three forms are found in the Calcarae, but only the leucon type is seen in the Demospongiae
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Copyright © 2002 by A. Richard Palmer. All rights reserved.
(revised Feb. 3, 2002)