MARINE
Invertebrates
BIOL 505
Understanding Marine
Invertebrates,
Their Environments
and Processes
Poriferans
Poriferan General Features
Phylum Porifera
Defining characteristic: collar cells (choanocytes) with
microvilli surrounding a flagella. Arise from single cells
or syncytia.
Most spp. (98%) are marine. No terrestrial.
5,000 – 10,000 extant spp.
Lack nervous system, musculature, locomotion,
specialized reproductive, digestive, respiratory, sensory,
or excretory systems. No organs at all!
No oral, anterior, or posterior regions.
Poriferans
Poriferan General Features
Only few cell types within individual, but cells function
independently.
When dissociated, cells dedifferentiate into amoeboid
cells, reaggregate, then redifferentiate to form sponge.
Amazingly, sponge cells can recognize other spp., as
well as self cells within same spp. Demonstrated in >25
spp.
Multicelluar? Or organized colonial living by individual
cells?
Poriferans
Poriferan General Features
Typically fairly rigid, perforated bag with inner surface
lined with flagellated cells (choanocytes or collar
cells).
Empty space inside sponge – spongocoel.
Choanocytes:
1. Generate current for ventilation of water through
sponge.
2. Capture food particles
3. Capture incoming sperm for reproduction.
Poriferans
Poriferan General Features
Next to choanocyte layer is layer of gelatinous, nonliving material – mesohyl (“middle stuff”). Although
non-living and acellular, it contains amoeboid cells –
archeocytes that wander through mesohyl by
cytoplasmic streaming.
Poriferans
Poriferan General Features
Archeocytes:
1. Digest food material captured by choanocytes.
Digestion completely intracellular.
2. Store digested food
3. Can differentiate into sperm (flagellated) or eggs
(although gametes can develop through changes to
choanocytes, too!).
4. Likely participate in non-self recognition in contact
with other sponge spp.
5. Act to eliminate waste material.
Poriferans
Poriferan General Features
Archeocytes:
6. Can become specialized to secrete structural elements
in the mesohyl – spicules made of either Si, or
CaCO3 , or fibers made of spongin protein.
Cells secreting spicules – “sclerocytes”
Cells secreting spongin – “spongocytes”
Both derived from archeocytes.
Poriferans
Poriferan General Features
Poriferans
Poriferan General Features
Archeocytes:
Spicules and fibers from spongocytes and sclerocytes
are:
1. used for spp identification (systematics)
2. used by sponge for support, shape, and discouraging
predation.
Poriferans
Poriferan General Features
Archeocytes:
Gemmule formation.
At certain times, sponges produce dormant structures –
gemmules.
1. Archeocytes gather nutrients by phagocytosis.
2. Archeocytes aggregate and cells around the cluster
form a thick capsule around the cluster.
3. When conditions are right, living cells leave the
gemmule and differentiate to form a functional
sponge.
Poriferans
Poriferan General Features
Archeocytes:
Gemmule formation.
Gemmules are more resistant to freezing, desiccation,
anoxia than the sponge that produces it.
They provide mechanism for withstanding unfavorable
conditions by entering period of dormancy.
Gemmule formation can be a form of asexual
reproduction, resulting in many offspring genetically
alike.
Poriferans
Poriferan General Anatomy
Pinacocytes - outer epithelial layer of most sponges,
composed of flattened, contractile cells. Lack a basal
lamina.
Form an outer layer – pinacoderm.
Also form inner layer lining incurrent canals and
spongocoel where there are no choanocytes.
As pinacocytes contract, causes slight shape changes in
sponge and may also help regulate water flow
through incurrent openings.
Poriferans
Poriferan General Features
Poriferans
Poriferan General Anatomy
Ventilation
Because sponges don’t really move and have no muscles
or nerves, they rely on water flow for removing
waste, bringing food, gas exchange, movement of
sperm.
Partly due to action of choanocytes, and partly due to
architecture of the sponge (Bernouli’s principle),
water flow is efficiently utilized by the sponge.
Water flows into the sponge and into the spongocoeld
through ostia (small openings around the sponge),
and out of the sponge through the osculum (large
opening of the spongocoel.
Poriferans
Poriferan General Anatomy
Ventilation
Ostia are always plentiful, but depending on the
structure of sponge, may only be one osculum.
Large sized sponges must filter large volumes of water
per day to obtain sufficient food material.
But water moving too fast will not allow food extraction.
Instead, water flow is slowed in the choanocytes and
speeds up again after entering spongocoel.
Poriferans
Poriferan Diversity
3 basic levels of sponge shape:
1. Asconoid – simple, basic tube structure with one
osculum.
2. Syconoid – increased degree of evagination with one
osculum.
3. Leuconoid – most complex evagination, with
multiple oscula.
Increased evagination away from spongocoel increases
extent of flagellated surface area enclosed by sponge.
Most sponges are of leuconoid structure.
Poriferans
Poriferan Diversity
Spongia sp ?
Poriferans
Poriferan Diversity
All sponges are placed in 3 classes based mainly on the
chemical structure and morphology of the support
structures (spicules).
1. Class Calcarea
2. Class Demospongiae
3. Class Hexactinellida
Poriferans
Poriferan Diversity
1. Class Calcarea
Have spicules made only of
CaCO3.
Class is represented by all 3
types of construction.
All living asconoids are in
this class.
Poriferans
Poriferan Diversity
2. Class Demospongiae
Largest class (>80% of all sponge spp.)
Have spicules made of spongin and/or silica, but
never CaCO3.
Some spp. Have no spicules or fibers.
All freshwater sponges (~300 spp.) in this class, and
possess contractile vacuoles!
Contains a group of deep water, carnivorous sponges
(with no ostia, no oscula, nocanal system and no
choanocytes) feed by entrapping small crustaceans.
Poriferans
Poriferan Diversity
2. Class Demospongiae
Liosina sp?
Xestospongia sp
Poriferans
Poriferan Diversity
3. Class Hexactinellida.
Sponges with six-rayed, silica spicules.
“Glass sponges”
Structurally complex and symmetrical.
May be either syconoid or leuconoid.
Different than other classes because outer layer is
syncytial (have several nuclei in single cytoplasmic
membrane) rather than cellular, and no
pinacoderm layer.
Poriferans
Poriferan Diversity
3. Class Hexactinellida.
Inner layer also syncytial.
Long, thing (~50 um d) silica
fibers produced at base of
Hexactinellida sponges convey
light better than synthetic fiber
optics and are structurally
superior.
Poriferans
Poriferan Reproduction
Sponges reproduce both asexually (fragmentation,
buds and gemmules), or sexually (eggs and
sperm).
Many spp. Hermaphroditic.
Fertilization and early development usually internal.
In some spp. Choanocytes capture incoming sperm,
dedifferentiate to become amoeboid cells, then
transport sperm to mesohyl where egg is fertilized.
Poriferans
Poriferan Reproduction
Steps.
1. In some spp. Choanocytes capture incoming
sperm,
2. dedifferentiate to become amoeboid cells,
3. transport sperm to mesohyl where egg is fertilized.
4. Retain developing embryo for some time.
5. Release of swimming larvae through oscula.
A few spp. are oviparous; fertilized eggs shed into
water and embryonic development external.
Psuedospongioformus bobulous larvae
Poriferans
Poriferan Reproduction
Embryonic Development.
In Calcareous sponges.
1. Embryo develops into hollow coeloblastula.
2. In some spp. fast dividing cells at one end become
flagellated toward blastocoel.
3. Along slower cell division region, blastula breaks
open.
4. Flagellated cells now outside.
5. Flagella propels larva (amphiblastula) through
water flagellated end first.
Poriferans
Poriferan Reproduction
Embryonic Development.
In Calcareous sponges.
6. In some spp. the initially hollow coeloblastula fills
with cells that detach from blastula wall.
7. Fill the blastocoel.
8. Termed stereoblastula.
Poriferans
Poriferan Reproduction
Embryonic Development.
In Demosponges.
1. Most embryos develop directly into
stereoblastula.
2. Differentiate to highly flagellated parechymella
(or parenchymulla) larvae, where each cell has
its own flagellum.
3. Some parenchymella larvae posses spicules,
choanocytes, and basic canal systems.
Poriferans
Poriferan Reproduction
Embryonic Development.
In Hexactnella.
1. Most embryos develop directly into
stereoblastula.
2. Differentiate highly and posses siliceous spicules,
choanocytes, and basic canal systems.
3. Only cells in the larval midsection flagellated.
4. Each cell has several flagella.
Poriferans
Poriferan Reproduction
Embryonic Development.
Sponge larvae cannot feed.
Usually swim for <24 hrs before settling.
Once attached to substrate, cells from different parts
of the larva migrate and differentiate and begin to
form the adult sponge.