Porifera - First up: The major lineages of evolution in...

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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) 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 neither look nor behave like animals and 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”). asymmetrical , sessile (attached) flter-Feeders simplest metazoans with only a cellular grade of organization (no true tissues & no embryonic germ-tissue layers) - different cell-types become specialized parts of a whole organism; these cells cannot live alone as do unicellular protozoan cells (e.g., Amoeba , Paramecium ), so… … perhaps evolved from a colonial protozoan? cells removed from sponges can reaggregate and reorganize/ regenerate the sponge organism, something not possible with adult animals that have tissues Evolution & characteristics:
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2 Beating fagellated collar cells (= choanocytes ) produce water currents that fow through incurrent pores in the sponge wall termed ostia (singular ostium) into canals or a central cavity and out through the osculum (a 10 cm tall sponge will Flter as much as 100 liters/ day.) Basic architecture (all sponge types) “ostia” *** *** Sponge Canal Systems Three types: 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 * * * (ostium) * * (see ±ig. 6.8, b) = water fow = ²ood route Choanocytes have a “collar” o² microvilli that Flter & trap ²ood particles ²rom fowing water that get phagocytized (= engul²ed) by the cell body.
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3 Choanocytes (“collar cells”) line the interior body walls of sponges. They have a central fagellum that is surrounded by a collar oF microvilli . Their resemblance to the single-celled choanoFagellate protists suggests sponges may be derived from unicellular choanofagellates that were colonial. The flagellum beats & pumps water through the sponge, while the microvilli of the “collar” trap food particles & send these to the cell body to be phagocytized. note transFer oF Food particles From 1 cell to another (see ±ig. 6.4) = water Fow mesohyle archaeocyte/amoebocyte cell types and water flow through an asconoid sponge (be able to identify and label these terms) Pinacocytes - outer sponge cells; thin, leathery and tightly packed together and collectively form the “ pinacoderm
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This note was uploaded on 06/29/2010 for the course BSC2011L BSC2011L taught by Professor Spears during the Summer '10 term at FSU.

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Porifera - First up: The major lineages of evolution in...

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