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Kingdom Animalia. Invertebrates- Phylum Porifera. Sponge Structure. Bodies completely lack symmetry (asymmetrical) Masses of specialized cells embedded in gel-like substance of body wall called mesohyl
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Kingdom Animalia Invertebrates- Phylum Porifera
Sponge Structure • Bodies completely lack symmetry (asymmetrical) • Masses of specialized cells embedded in gel-like substance of body wall called mesohyl • Totipotent- The plasticity of sponge cells and how specialized types can change into others • Not organized into tissues nor organs (Parazoa) • Body wall covered in tiny pores, ostia, water enters • Larger openings, oscula, water exits • Sessile- Do not move • Attach to surface early in life • Can produce toxins as defense
Sponges • Pinacoderm- Outer layer of cells of a sponge • Pinacocytes- Thin, flat cells on the outer-surface • Can be tube-like and contractile (porocytes) • Bag-shaped with large internal cavity (Spongocoel) • Lined by choanocytes, or collar cells (Choanoderm collectively) • Flagellated cells draw in water through pores • Amoeboids (Mesenchyme cells)- Irregularly shaped sponge cells • Float in mesohyl to supply nutrients and carry away waste for other cells
Protistan Ancestors • Choanocytes closely resemble a protist called a choanoflagellate
Feeding Habits of a Sponge • Collar cells function as sieves • Trap plankton and other tiny organisms in the small hair-like projections • Pulls organisms in and digests them intracellularly (within the cell) • Release nutrients and waste into mesohyl • Amoebocytes pick up nutrients from mesohyl and supplies to rest of cells
Sponge Skeleton • Skeletal support is to prevent sponge from collapsing in on itself • Not a fixed skeleton, parts found throughout mesohyl • Most sponges composed of spicules • Tiny needles composed of silica or calcium carbonate • Used for protestion as well • Sclerocyte- Cells that produce spicules • Microscleres- Smaller spicules • Macroscleres- Larger spicules • Few composed of spongin (ex: bath sponges) • Resilient, flexible protein fibers • Some contain both http://player.discoveryeducation.com/index.cfm?guidAssetId=287F0044-982C-4BA6-90E9-BC5863CFB205
Three Types of Sponges • Based on skeleton type • Class Calcarea- Calcareous sponges • Spicules composed of calcium carbonate • Class Hexactinellida- Glass sponges- Found in the deepest parts of the ocean • Spicules made of silica • Hexaxon- Unique six-pointed spicule • - Class Demospongiae- Demosponges • Spicules made of silica • Also contain spongin (proteinaceous)
Three Body Forms • Ascon- Vase-like Porocytes (ostia) lead directly to spongocoel • Sycon- sponge wall is folded. • incurrent canals -water enters from dermal pores • radial canals (lined with choanocytes)- lead to spongocoel • Leucon- Branched canal system lacking spongocoel • Incurrent canals lead to choanocyte- lined chambers (water slows through these) • Multiple oscula from excurrent canals
Reproduction • Asexual reproduction: • Regeneration- Cut pieces will grow back • Budding- Shed fragments constantly to make new individuals • Gemmules- Amoebocytes encased in protective coat • Develop when living conditions become to harsh to survive • Sealed in with food to survive • Cells grow into new sponge when conditions
Reproduction • Sexual reproduction • Most sponges are hermaphrodites (produce both eggs and sperm • Do not self fertilize • Sperm cells of one sponge enter another through pores • Collar cells pass sperm into mesohyl where eggs are located and fertilization occurs • Zygotes develop into larvae and leave the sponge • Inversion- movement of flagellar cells of developing larvae to the outside • Blastula- Hollow larval stage (coeloblastula) • Parenchymula- Solid larval stage • Macromeres- Large cells that form the outer choanoderm • After a brief free-swimming stage they attach to a surface to live as sessile sponges
