Biology 320 Invertebrate Zoology Fall 2005

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Biology 320Invertebrate ZoologyFall 2005

• Chapter 5 Phylum Porifera

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Phylum Porifera

• The sponges
• Name Porifera means pore bearers
• First metazoan phylum we will discuss
• Posses epithelioid and rudimentary connective
  tissue
• Lack true muscle and nervous tissues
• Not considered to be eumetazoans

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• Approximately 8000 spp. of sponges
• Mostly marine, with approx. 150 described
  freshwater spp.
• Primitive, sessile filter feeders
• Most are asymmetrical, but some display radial
  symmetry
• Can be erect, branching, or encrusting on
  substratum

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Body Design

• Three main forms of sponges, classified according
  to complexity
• Asconoid
• Syconoid
• Leuconoid
• Asconoid sponges
• Simplest body plan
• Resemble a hollow tube, with the base attached to
  the substrate
• Possesses one large spongocoel lined with a
  single layer of choanoderm
• Choanocytes beat and draw water through ostia in
  the epidermis

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• Asconoid sponges cont
• Water exits spongocoel through a single large
  osculum
• Smallest of all sponges (1mm in diameter)
• Thinnest body walls
• Leucosolenia
• Growth is limited by spongocoel diameter
• If asconoid sponges had larger diameters, body
  volume would exceed pumping capacity of
  choanoderm
• Therefore, a only a change in this simple body
  plan would permit the evolution of larger body
  sizes in sponges

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• Syconoid Sponges
• Body wall contains pockets, known as choanocyte
  chambers, that are lined with choanoderm
• Increases choanoderm surface area
• Decreases spongocoel volume
• Larger than asconoid sponges (one cm a few cm)
• Body walls are thicker than in asconoid sponges
• Grantia and Sycon (formerly Scypha)

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• Leuconoid sponges
• Contains thousands of choanocyte chambers,
  thereby further increasing the choanoderm SA
• Spongocoel is further reduced
• Therefore, these are the largest sponges (few cm
  to one meter, or more)
• Thickest body walls
• May possess more than one osculum

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Body Wall Composition

• The body walls of sponges are classified as
  either being cellular or syncytial
• Cellular sponges have two primitive primary
  tissues
• Epithelioid resembles epithelium
• Mesohyl connective tissue middle layer
• There are two specific types of epithelioid
  tissue
• Pinacoderm lines inside (except where
  choanoderm is present) and outside
• Choanoderm choanocytes posses a flagellum and
  collar of microvilli

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• Mesohyl is a fibrous (proteinaceous) ECM
  containing cells and skeletal elements
• All mesohyl cells are totipotent and amoeboid
• Archeocytes can differentiate into any type of
  sponge cell. Aide in digestion (via
  phagocytosis) and internal transport
• Lophocytes secrete and maintain collagen fibers
• Spongocytes responsible for producing thick
  skeletal fibers known as spongin

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• Mesohyl cells cont
• Sclerocytes secrete spicules, interesting
  skeletal elements made of silica or calcium
• Myocytes essentially muscle cells usually
  concentrated around osculum. Constrict or dilate
  to control water flow
• Germ cells reproductive cells

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• Syncytial sponges DO posses cells, but not at the
  same level of organization as cellular sponges
• Cytoplasm is continuous and lacks membranes that
  compartmentalize separate cells
• Lack pinacoderm
• Lack choanoderm. Posses collar bodies instead
  these are located in collar body chambers,
  individually rather than in epitheliod sheets
• Mesohyl is present and contains archeocytes,
  sclerocytes, and germ cells

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• Syncytial sponges cont
• Body wall resembles a 3D cobweb-like pattern and
  is called a trabecular syncytium
• Each strand of the trabecular syncytium encloses
  an axis of mesohyl
• Collagen and spicules are present

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Taxonomy

• Two subphyla
• Subphylum Symplasma (Hexactinellida)
• Subphylum Cellularia
• Subphylum Symplasma consists of glass sponges
  that posses syncytial tissues
• Most sponges belong to Subphylum Cellularia,
  which is divided into two main classes, both
  possessing cellular tissues
• Class Demospongiae have siliceous spicules and
  spongin
• Class Calcarea have calcareous spicules

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Skeleton

• Any cell, organism, etc. needs some form of
  support
• Mesohyl acts as an endoskeleton
• Diversity of mesohylar structure
• Fine collagen fibers only
• May be supplemented with spicules, spongin, or
  both
• Incredible diversity of spicules and some can
  project through mesohyl to protect the outside of
  the sponge

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Water Pumping

• Most pump a volume of water equal to their body
  volume, every 5 seconds
• Can slow / stop water flow to avoid taking in
  silt
• Can control rate of water flow via
• Contracting or relaxing myocytes, which controls
  osculum diameter
• Closing ostia
• Adjusting flagellar beat of choanoderm / collar
  bodies

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Locomotion

• Some have limited capacity for locomotion
• Can move 1 to 4 mm per day
• Result of collected amoeboid movement of cells
• Osculum contraction
• Whole body contraction

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Nutrition

• Filter feeders
• Typically phagocytize particles of 50µm or less
• Particle size determines which cells phagocytize
• All cells can phagocytize
• Choanocytes transfer particles to vacuoles for
  digestion
• Archeocytes remove wastes / inorganics from system

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• Feed on dinoflagellates, bacteria, viruses,
  debris, etc.
• Some are carnivorous (dont filter) trap small
  animals such as crustaceans

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• May posses photosynthetic endosymbionts
• Cyanobacteria
• Dinoflagellates
• Chlorophytes
• Symbionts may cause sponge to be brightly colored
• Sponges must live in shallow water to
  photosynthesize
• Some obtain up to 80 of nutrients from
  photosynthate

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Internal Transport

• Gas / waste transport is carried out via simple
  diffusion
• Sponges are leaky, so water penetrates almost
  the entire animal
• Sheets of cells are only one cell layer thick
• Mobile amoeboid cells
• Ammonia is the main metabolic waste
• Almost always the case for animals in aqueous
  environments
• Uric acid or urea in terrestrial habitats
• Archeocytes transfer wastes / nutrients
• Some individual cells posses contractile vacuoles

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Nervous Tissue

• Lack nerve cells
• Some have localized impulses responsible for
  myocyte contraction
• Glass sponges can generate action potentials that
  travel all across their syncytium at a rapid rate
• Used to arrest flagellar beating

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Ecology

• Many produce toxins to prevent predation
• Some animals are spongivores
• Nudibranchs
• Fish
• Turtles Hawksbill turtle feces can be up to 95
  siliceous spicules
• Some release chemicals that kill competing
  sessile organisms, such as corals

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• Some animals such as shrimps and brittle stars
  live in sponges
• Decorator crabs may place sponges on their
  carapaces
• Cliona breaks down calcareous shells. Bores into
  shells for protection

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Reproduction

• Sponges are excellent regenerators
• Reproduce clonally through several methods
• Fragmentation usually due to wave damage or
  grazing
• Budding
• Gemmules (winter bodies) spore-like structures
  that are essentially a mass of nutrient-laden
  archeocytes that are surrounded by a shell.
  Undergo diapause

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• Sponges frequently reproduce sexually
• Sponges are hermaphrodites (monoecious)
• Germ cells occur throughout mesohyl
• Choanocytes can also release sperm, and form eggs

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• Sperm are broadcasted into water column
• Choanocytes phagocytize incoming sperm, but dont
  digest
• They differentiate into an amoeboid cell and
  deliver sperm head to egg
• Most eggs are fertilized through phagocytosis
  (therefore, most sponge sperm lack an acrosome)

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• Some sponges are oviparous, and release zygotes
  into water column
• Most are viviparous, and retain zygotes in their
  body, later releasing larvae
• Sponge larvae are very diverse

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• Larvae are short lived
• Settle within a few days
• Creep across substrate until a suitable spot is
  found
• Metamorphose into a juvenile
• Varied lifespans
• May live one to a few years in temperate zones
• Tropical or deep sea spp. May live 200 years or
  more
• Some only grow 0.2 mm/yr, and could be 5000 years
  old if that growth rate is constant