Kingdom Animalia

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Kingdom Animalia

• Invertebrates- Phylum Porifera

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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

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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

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Structure of a Sponge
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Protistan Ancestors

• Choanocytes closely resemble a protist called a
  choanoflagellate

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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

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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
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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)

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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

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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

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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

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Sexual Reproduction of Sponges