Invertebrate Zoology

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Invertebrate Zoology

• Lecture 5 Phylum Porifera

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Lecture outline

• Phylum Porifera
• Overview
• Body structure and the aquiferous system
• Nutrition, excretion and gas exchange
• Activity and Sensitivity
• Reproduction
• Reaggregation
• Protection
• Sponges as habitat
• Sponges and Humans

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Overview

• Considered to be plants until 1765.
• Diversity three major groups
• 1. Calcarea Calcareous sponges
• Calcium carbonate (calcite) spicules
• Primarily shallow water and tropical (some
  exceptions)

Photo www.meer.org
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Overview

• Diversity three major groups
• 2. Hexactinellida Glass Sponges
• Siliceous, 6-rayed spicules
• Marine, primarily deep water

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Overview

• Diversity three major groups
• 3. Demospongiae Demosponges
• Siliceous spicules (never 6-rayed) and/or spongin
  for support

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Overview

• Simplest multicellular animals
• Considered "multicellular" rather than colonial
  because there are different cell types.
• Key cell type, the choanocyte, resembles a cells
  of a choanoflagellate (Protista)

Choanoflagellate
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Overview

• Key characteristics (see Box 6A)
• Metazoa
• No true tissues or body systems of any type
• Not much, if any. coordination among cells
• Layers lack basement membrane
• Adults are asymmetrical or superficially radially
  symmetrical
• Totipotent cells like stem cells!
• Choanocytes drive water through the various
  canals and chambers aquiferous system

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Overview

• Key characteristics (cont.)
• Almost all species are sessile suspension feeders
• Larvae are motile, usually lecithotrophic
  (dispersed, not brooded carry significant yolk
  supply non-feeding)
• Mesohyle (middle layer) includes motile cells
  plus supporting material (i.e. spicules, spongin)
• Skeletal elements composed of calcium carbonate,
  silicon dioxide and/or collagen

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Body structure/aquiferous system
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Body structure/aquiferous system

• Surface
• Pinacocytes
• cover outside line pores/passageway
• flattened, single cell width
• No basement membrane
• Collagen, may cover sponge instead
• ostia (pores) perforate the pinacocyte layer
  (tiny)
• Porocytes in some sponges
• osculum main exit (large)

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Body structure/aquiferous system

• Main matrix of sponge mesohyle
• Non-cellular, colloidal matrix
• Skeletal elements
• Collagen (spongin)
• Spicules
• composed of calcium carbonate or silicon dioxide
• Often used in sponge ID
• myocytes
• contractile cells that surround major openings
  and channels (not shown)

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Focus spicules
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Body structure/aquiferous system

• Main matrix of sponge mesohyle
• Amoebocytes ( archaeocytes)
• Move in amoeboid fashion
• highly mobile
• Secrete spicules spongin
• Complete the process of digestion
• Store food
• Transport waste to excurrent pore
• Totipotent
• Control of flow rates (How?)
• May leave parent sponge and then return
• Can move the entire sponge

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Body structure/aquiferous system

• Choanocytes key cell type, inner surface
• Provides water current by beating its flagellum
• Beating of flagella is not coordinated
• Captures and engulfs food particles ?
  intracellular digestion

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Body structure/aquiferous system

• Structural conditions of sponges
• Refers to degree of folding and complexity

Ascon Sycon Leucon
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Body structure/aquiferous system

• Structural conditions of sponges
• Trend from one large chamber to numerous small
  chambers.
• Ascon one main chamber (spongocoel) lined with
  choanocytes
• Sycon choanocyte chambers off the spongocoel
• Leucon has multiple layers of choanocyte chambers

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Body structure/aquiferous system

• Consequences of increased complexity
• More surface area for?
• Higher flow rates (overall)
• Causes?
• Advantages of higher flow rates?
• Potential problems of ?flow?
• Where in sponge must flow rates drop and why?
• What causes this slowing?
• NOTE Water current adds to internal current
  created by flagella

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Nutrition

• Water flow brings in food
• Size selectivity at several levels
• Ostia, 5-50 µm small phytoplankton, bacteria,
  detritus
• Ameobocytes, 2-5 µm (smaller phytoplankton,
  bacteria, detritus)
• Choanocyte collar 0.5 1.5 µm (bacteria,
  viruses, larger organic molecules)

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Nutrition

• Food capture by choanocytes
• Beating of flagellum creates negative pressure
  inside collar, draws food to outside of
  mucus-covered microvilli of collar
• What are microvilli made of?

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Nutrition

• Food capture by choanocytes (cont.)
• Food particles caught in mucus, moved via cilia
  (?) or undulations of the collar to cell body
• Food phagocytosed, digested
• Food capture by amoebocytes
• Directly
• Transfer from choanocytes

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Nutrition

• Carnivorous sponges Family Cladorhyzidae!
• Stalked tentacle-like extensions covered with
  hook-like spicules capture prey
• Individual cells engulf and digest prey
  (intracellular)
• Symbionts provide nutrients to some sponges
• Methanotrophic bacteria (in some carnivorous
  sponges!)
• Photosynthetic protists

Photo Michel Phlibert
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Excretion/osmoregulation

• Excretion (ammonia) via diffusion over individual
  cells
• Dissolved ammonia is swept out the osculum via
  water currents
• Water expulsion vesicles (WEV) in freshwater
  sponges

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Gas exchange

• Oxygen brought in with water
• Gas exchange via diffusion (individual cells)
• Dissolved carbon dioxide is swept out the osculum
  via water currents

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Activity and Sensitivity

• No nervous system or discrete sense organs
• Respond to touch (some will close off
  ostia/osculum)
• Respond to excessively high particle
  concentration
• Close off ostia (via myocytes) ? flagellar
  beating
• Some have endogenous rhythmicity
• Takes a few minutes for the entire sponge to
  change rates
• Cells communicate mechanically and chemically
• ?current generation reorganization or
  reproduction
• Class Hexactinellida have a syncytium which can
  conduct electrical signals along its membrane
• Much slower than true neurons.
• Apparently controls water flow into the sponge

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Activity and Sensitivity

• Movement
• Most species are sessile as adults
• Cells frequently move and rearrange themselves
• Amoebocytes are highly mobile
• One species, Tethya seychellensis, Red Sea, has
  sticky, filamentous extensions
• Filaments contract and pull sponge along.

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Sponge reproduction asexual

• Fragmentation ? Regeneration
• Budding ? buds fall develop into a new sponge
• Gemmules resting stage
• Family Spongillidae (freshwater)
• Withstand freezing drying
• Gemmule structure
• Archaeocytes aggregate
• Layer of spongin and spicules
• Micropyle small opening

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Sponge reproduction asexual

• Gemmules (cont.)
• Good conditions Archaeocytes migrate out through
  the micropyle, reconstruct sponge

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Sponge reproduction sexual

• Overview
• Most sponges are protandrous or protogynous
  hermaphrodites
• A few are gonochoristic
• Some species have both hermaphroditic and
  gonochoristic individuals in the same population
• No gonads
• Sperm production choanocytes transform into
  spermatogonia (in choanocyte chambers or after
  migrating into the mesohyle.
• Egg production choanocytes or amoebocytes
  transform into oocytes

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Sponge reproduction sexual

• Location of fertilization
• In the water column (both eggs and sperm are
  spawned)
• Within the body of the sponge (sperm spawned,
  eggs retained)
• Gametes are released via the osculum
• Example Sperm release, barrel sponge

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Sponge reproduction sexual

• Specifics of fertilization (for retained eggs)
• Sperm enters choanocyte, loses tail, is encased
  in a vesicle inside choanocyte
• Choanocyte is transformed (loses collar
  flagellum)
• Transfer choanocyte moves, attaches to an egg,
  transfers the sperm to the egg
• Fertilization occurs

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Sponge reproduction sexual

• Zygote ? larva one type is an amphiblastula
  larva

• Flagellated cells inside first, then the whole
  larva turns inside out
• Larvae released with flagellated cells on outside
• Leaves via osculum

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Sponge reproduction sexual

• Upon settlement, flagellated cells move from
  outside to inside via invagination

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Reaggregation of sponges

• Dissociated cells find each other, reform a
  functional sponge
• Can learn about cell-cell recognition
  development cell differentiation
• Some only reaggregate with members of same
  species, others more flexible
• May help us to understand tissue rejection

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Protection

• Spicules
• Toxins/warning coloration
• Toxic secondary metabolites within spherulous
  cells (type of amoebocyte)
• Some sponge toxins useful to humans
• anti-cancer, anti-viral and anti-bacterial
• NOTENudibranch predators co-opt sponge defenses
  (toxins, spicules)
• Regenerative ability
• Camouflage (if not toxic)
• Bore into shells (parasitic)

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Sponges and humans

• Medical uses (just mentioned)
• Bath sponges
• Sponge farms in some regions
• Sponges over-harvested in Greece, Bahamas
• Declines due to fungal and viral diseases in some
  regions.