PoriferaSlides - 1 First up Phylum Porifera(“pore...

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Unformatted text preview: 1 First up: Phylum Porifera (“pore bearers”)-the sponges- ~10,000 living species, mostly marine (Chapter 6) The major lineages of evolution in animals Fundamental evolutionary divergence among metazoan (multicellular) Animalia, but based on what? (cellular vs. tissues) INTRO: THESE ARE ANIMALS?! WHY? Sponges have a long evolutionary history with more than 1000 fossil forms identiFed, the earliest of which is 550 million years old. Sponges were not accepted as animals until the mid 19th century. Hence their grouping in the grade “Parazoa” (“alongside” animals). Sponges are multicellular heterotrophs (hence, “animals”). • Symmetry: asymmetrical • Organization: simplest metazoans with only a cellular grade of organization (no true tissues & no embryonic germ-tissue layers) • specialized cell-types form parts of a whole organism; • cells cannot live alone as do unicellular protozoan cells (e.g., Amoeba , Paramecium ), so… • Very cool: cells removed from sponges can reaggregate and reorganize/regenerate the sponge organism, something not possible with adult animals that have tissues 2 • Locomotion: none; sessile (attached to substrate ) • Sensory/nerves: no specialized structures • Circulation/transport: no specialized structures (diffusion & cell- to-cell) • Osmoregulation/excretory: no specialized structures; simple diffusion with environment (water) • Respiration: simple diffusion with environment (water) • Feeding: suspension/Flter feeders with intracellular digestion • Reproduction: mostly monoecious (usually “sequential” hermaphrodites); both sexual & asexual modes Beating ¡agellated collar cells (= choanocytes) produce currents that bring water & food into incurrent pores in the sponge wall termed ostia (singular ostium) into canals or a central cavity and out through the osculum opening (a 10 cm tall sponge will Flter as much as 100 liters/ day.) Basic architecture (all sponge types) “ostia” *** *** Sponge Canal Systems Three types of sponge architecture: • asconoid (simplest) • syconoid • leuconoid (most complex) (see ¢ig. 6.4) asconoid sponge structure and function (basic “in/out” water flow) osculum NOTE: the spongocoel or atrium is lined with flagellated & beating “collar cells” called choanocytes . * (ostium) (spongocoel) ostium 3 (see Fig. 6.8, b) = water fow = ¡ood route Feeding: choanocytes have a “collar” o¡ microvilli that trap ¡ood particles ¡rom fowing water that get phagocytized (= engul¡ed) by the cell & passes on to other cells (amoebocytes); can become sperm Digestion: intracellular The flagellum beats & pumps water through the sponge, while the microvilli of the “collar” trap food...
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PoriferaSlides - 1 First up Phylum Porifera(“pore...

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