Invertebrate Zoology
Lecture 5: Phylum Porifera
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
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
Overview
 Diversity: three
major groups

2. Hexactinellida:
Glass Sponges
 Siliceous, 6-rayed
spicules
 Marine, primarily
deep water
Overview
 Diversity: three
major groups

3. Demospongiae:
Demosponges
 Siliceous spicules
(never 6-rayed)
and/or spongin for
support
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
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”
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
Body structure/aquiferous system
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)
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)
Focus: spicules
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
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
Body structure/aquiferous system

Structural conditions of sponges:
 Refers to degree of folding and complexity
Ascon
Sycon
Leucon
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
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
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)
Nutrition

Food capture by choanocytes

Beating of flagellum creates negative pressure
inside collar, draws food to outside of mucuscovered microvilli of collar
 What are microvilli made of?
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
Nutrition

Carnivorous sponges:
Family Cladorhyzidae!
 Stalked; tentacle-like
extensions covered with hooklike 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
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
Gas exchange
 Oxygen brought in
with water
 Gas exchange via
diffusion (individual
cells)
 Dissolved carbon
dioxide is swept out
the osculum via
water currents
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
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.
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
Sponge reproduction: asexual
 Gemmules (cont.)
Good conditions: Archaeocytes migrate out
through the micropyle, reconstruct sponge
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
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
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
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
Sponge reproduction: sexual
Upon settlement, flagellated cells move from
outside to inside via invagination
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
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
 NOTE:Nudibranch predators co-opt sponge
defenses (toxins, spicules)



Regenerative ability
Camouflage (if not toxic)
Bore into shells (parasitic)
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.