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• 1) Metazoa=Animalia: capable of movement, heterotrophic, multicellular, pass through a blastula stage, possess collagen

• 2) Origin of Metazoa. Choanoflagellates are the likely living sister group; they share key characters with primitive metazoans:

  • a) cells with single cilium/flagellum (=monociliated) surrounded by ring of microvilli

  • b) diplosome- curious anchoring structure for flagellum

• 3) Metazoa exhibit substantial cell specialization: 'division of labor' permits tremendous diversity of form (differentiation & integration)

• 4) Porifera (sponges) are sessile, show the least cellular differentiation & integration of metazoans and lack true tissues, endoderm, mouth & gut (cellular level of organization); difficult to distinguish from colonial protists; hence sometimes placed in subkingdom Parazoa

• 5) Three classes of note: Calcarae, Demospongiae, Hexactinellida

• 6) Specialized cells include: epithelial-like cells, collar cells (pumping, feeding), porocytes (incurrent pores), mesenchyme cells (make spicules, spongin), contractile cells (encircle excurrent pores)

• 7) Common features of the water-canal system are: multiple (small) incurrent pores, only one or a few (large) excurrent pores

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• 8) Colony form varies from simple (ascon type- single pumping cavity) to intermediate (sycon type- multiple radial pumping canals) to complex (leucon type- many distinct flagellated chambers)

• 9) Collar cells feed like choanoflagellates: phagocitize tiny particles (bacteria, spores, gametes, fine organic debris, etc.) from water

• 10) Reproduction: hermaphroditic, internal fertilization, larval stage

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