Zoology 250 Lecture 6
INTRO. TO METAZOA; PHYLUM PORIFERA I
(Porifera study images)
- 1) Metazoa=Animalia: are capable of movement (most, contrasts with fungi and multicellular plants), heterotrophic, truly multicellular; they pass through a blastula stage & possess collagen
- 2) Porifera (sponges) are sessile; ~5000 marine, ~150 freshwater spp.
- 3)Sponges are bizarre and clearly very primitive; they show the least cellular differentiation & integration of all Metazoa
- 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)
- differ so much from other Metazoa that 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: <15 cm)
- DEMOSPONGIAE (silica spicules, with spongin in some; most successful group of sponges; can be large: >2 m)
- HEXACTINELLIDA (silica spicules, lack spongin; a very odd deep sea taxon; most are 10 - 30 cm)
- 5) Common features of the water-canal system are: 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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