Structure générale
Stade ascon d’Olinthus
Les spongiaires ou
porifères
Marc Girondot, Université Paris Sud
Types
cellulaires
de la paroi
Between the two
layers is a thin
space called
mesenchyme or
mesohyl. The
mesenchyme
consists of a
proteinaceous
matrix, some cells,
and spicules.
Sclérocytes et spongocytes
!
The secretion of spicules is carried out by sclerocytes.
Other cells, called spongocytes, secrete the spongin
skeletat fibres when those are present.
Spongin is a protein critical to the structure of sponges and
demosponges in the phylum Porifera. Spongin forms a sort of
skeleton for sponges, shaping spicules that consist of sponging
fiber which allow the free flow of nutrients into sponges while
providing support for the sponge.
90% of all sponges, use spongin as a major component. Because
it is a protein, sponging does not fossilize well.
Choanocytes
These distinctive cells
line the interior body
walls of sponges. These
cells have a central
flagellum that is surrounded by a collar of microvilli. It is their striking
resemblance to the single-celled protists called
choanoflagellates that make many scientists believe that
choanoflagellates are the sister group to the animals.
Choanocytes are versatile cells. Their flagella beat to create
the active pumping of water through the sponge, while the
collars of the choanocytes are the primary areas that
nutrients are absorbed into the sponge. Furthermore, in some
sponges the choanoflagellates develop into gametes.
Archeocytes
!
Archaeocytes are very important to the functioning of
a sponge. These cells are totipotent, which means that
they can change into all of the other types of sponge
cells. Archaeocytes ingest and digest food caught by
the choanocyte collars and transport nutrients to the
other cells of the sponge. In some sponges,
archaeocytes develop into gametes.
Myocytes et Porocytes
!
Poriferans do not have any muscle cells, so their
movement is rather limited. However, some poriferan
cells can contract in a similar fashion as muscle cells.
Myocytes and porocytes which surround canal
openings and pores can contract to regulate flow
through the sponge.
Le squelette
!
Formé de spicules siliceux,
carbonatés ou constitués
de matières organiques.
Calcarea
Demospongiae
Hexactinellida
Calcinea
Homoscleromorpha
Amphidiscophora
Calcaronea
Tetractinomorpha
Hexasterophora
Ceractinomorpha
Pinacocytes
!
Formation des spicules
A: a: diactine; b:
triactine; c:
tétractine
! B, C et D:
formation des
spicules di, tri et
tétractines.
!
Systématique: Archaeocyathes
!
Brusca, R.C., and G.J. Brusca. 2003. Invertebrates. Second Edition. Sinauer Associates, Sunderland, Massachusetts.
These cells are the "skin cells" of sponges. They line
the exterior of the sponge body wall. They are thin,
leathery and tightly packed together.
Archaeocyaths are an extinct group of sponges that had a very brief (geologically
speaking) and spectacular history. The first archaeocyaths appear roughly 530
million years ago, during the Lower Cambrian. Archaeocyath species were very
important members of Lower Cambrian communities. They diversified into
hundreds of species during this time period and some of these species contributed
greatly to the creation of the first reefs. Reef ecosystems tend to support a wide
variety of organisms both in the present and in the past. Despite their great success
in terms of numbers, the archaeocyaths were a short-lived group. They were almost
completely non-existent by the middle Cambrian, some 10 to 15 million years after
their first appearance.
Systématique: Hexactinellides
Squelette siliceux à trois axes
et six pointes (triaxonides
hexactinides), isolés ou en
groupe.
! Souvent de grande taille et le
plus souvent dotés d’une
symétrie axiale.
! Forme de fond calme.
L’euplectelle
Association entre une éponge et un couple de
crevette
!
!
Hexactinellida
Systématique: Calcarea
Spicules calcaire simples ou composés d’origine pluricellulaire.
!
!
!
!
Avec amphidisques, sans hexasters ....
AMPHIDISCOPHORA
Sans amphidisques, avec hexasters ....
HEXASTEROPHORA
A: stade sycon; B: stade leucon
Structure de la paroi
Calcarea is the only class
with asconoid and syconoid
construction. All others
have leuconoid
construction.
Amphidisque: plaque formée par les spicules
hexactines
Hexaster: rosette formée par les spicules hexactines
Détail de la paroi
!
!
Systèmatique des Calcarea
!
! Ap:
apopyle; At: Atrium; C. Ex. Canal exhalant; C. In. :
Canal Inhalant; C.V.: Corbeille vibratile: O. In.: Orifice
Inhalant; P. In. Pore inhalant; Pr. : Porocyte
!
Les deux groupes actuels d’éponges calcarea sont les
Calcinea et les Calcaronea. Ces éponges sont
caractérisées par des spicules régulières à 3 ou 4
branches.
The Calcinea is difficult to characterize and thus may
be paraphyletic. The Calcaronea is more likely a
monophyletic group of sponges since they share
characteristic larvae and nucleus position in
choanocytes, presumably due to common ancestry.
The Calcinea is known from the Permian, while
probable calcaronean fossils have been identified from
the Cambrian. Both groups persist with many
representatives in today's oceans.
Systématique: Démosponges
!
Type de paroi chez les démosponges
Spicules siliceux non triaxones, spicules
siliceux et fibres de spongine, fibre de spongine
seulement ou absence de spicules.
Sans et avec cortex
Synthèse de fibres
de spongine (A) et
relations entre
fibres de spongine
et spicules (B-E)
Systématique: Chaetidés
!
The chaetetids compose a small group of organisms that was most often
presumed to be among the anthozoan corals, more specifically allied to the
Tabulata. However, with the discovery of a living representative, it was learned
that chaetetids are actually sponges. Previously, chaetetids were known from the
Ordovician to the Miocene. The overall body form varied from flat encrusting to
upright columns. Some achieved a size of over 3 meters. Their fossil record
suggests that they were mostly warm shallow water organisms often associated
with photosynthetic algae. They apparently required hard substrates for
settlement and the onset of growth. They contributed to the development of reefs
during the Paleozoic and Mesozoic, both overgrowing and serving as substrate
for other reef-associated organisms.
The general chaetetid growth form can be described
as a cluster of closely packed tubes with floors or
tabulae. The rigid skeleton is calcareous. The living
chaetetid, Acanthochaetetes wellsi possesses
siliceous spicules and soft parts that clearly place it
within the demosponges. Spicules are rarely
preserved in fossil chaetetids. It is unknown if
chaetetids form a monophyleticgrouping, although the
hypothesis of monophyly has not been falsified at
this point in time.
Systématique:
Stromatoporoïdes
The stromatoporoids had massive calcareous skeletons that are preserved as rather
conspicuous fossils. A cross-section is shown above, while a view down on the living surface
is presented below. Some stromatoporoids formed domes in excess of 5 meters in diameter.
The stromatoporoid grew by secreting calcareous sheets. This growth process resulted in
layers, termed laminae, parallel to the substrate and rod-like pillars perpendicular to the
laminae. The layers closest to the surface of the skeleton probably contained living tissue;
those layers away from the surface appear to have been back-filled with calcite. The surface
of the skeleton, where most of the living tissue resided, has raised structures called
mamelons, presumably serving as sites for excurrent openings. Associated with mamelons
are canals called astrorhizae. Very similar structures, observed on living sponges of the genus
Astrosclera, represent excurrent canal systems. This is strong evidence that fossil
stromatoporoids were poriferans (demosponge).
Polyphyly of "sclerosponges" (Porifera,
Demospongiae) supported by 28S
ribosomal sequences
!
!
!
Chombard C, Boury-Esnault N, Tillier A, Vacelet J.
Laboratoire de biologie des Invertebres Marins et Malacologie (CNRS URA 699), Museum National
d'Histoire Naturelle, Paris, France
To test the competing hypotheses of polyphyly and monophyly of
"sclerosponges," sequences from the 5' end of 28S ribosomal RNA
were obtained for Astrosclera willeyana, Acanthochaetetes wellsi, and
six other demosponge species. Phylogenetic relationships deduced
from parsimony and neighbor-joining analyses suggest that these
sclerosponges belong to two different orders of Demospongiae:
Astrosclera willeyana, being closely related to the Agelasidae,
belongs to the Agelasida, Acanthochaetetes wellsi, being closely
related to the Spirastrellidae, belongs to the Hadromerida. These
results contradict the hypothesis that sclerosponges are monophyletic
and imply that a massive calcareous skeleton has evolved
independently in several lineages of sponges.
Reproduction
!
Fécondation
Sponges reproduce by both asexual and sexual means. Most poriferans
that reproduce by sexual means are hermaphroditic and produce eggs
and sperm at different times. Sperm are frequently "broadcast" into the
water column. That is, sperm are created, concentrated and sent out the
excurrent openings, sometimes in masses so dense that the sponges
appear to be smoking. These sperm are subsequently captured by
female sponges of the same species. Inside the female, the sperm are
transported to eggs by special cells called archeocytes. Fertilization
occurs in the mesenchyme and the zygotes develop into ciliated larvae.
Some sponges release their larvae, where others retain them for some
time. Once the larvae are in the water column they settle and develop
into juvenile sponges. Sponges that reproduce asexually produce buds
or, more often, gemmules, which are packets of several cells of various
types inside a protective covering. Fresh water sponges of the
Spongillidae often produce gemmules prior to winter. These then
develop into adult sponges beginning the following spring.
Ecologie
!
Développement de Sycon
Sponges come in an incredible variety of colors and an amazing array of
shapes. They are predominantly marine, with the notable exception of
the family Spongillidae, an extant group of fresh-water demosponges
whose fossil record begins in the Cretaceous. Sponges are ubiquitous
benthic creatures, found at all latitudes beneath the world's oceans, and
from the intertidal to the deep-sea. Generally, they are sessile, though it
has been shown that some are able to move slowly (up to 4 mm per day)
within aquaria. It is unknown whether this movement is important for
sponge ecology under natural conditions. Some sponges bore into the
shell of bivalves, gastropods, and the colonial skeletons of corals by
slowly etching away chips of calcareous material.
Cliona sp.
Le bernard l’hermite
Bernardhus impressus
Un cas particulier
L’avantage de l’utilisation de Suberites
domunculus
L’exception carnivore
!
Sponges of the family Cladorhizidae are especially unusual in
that they typically feed by capturing and digesting whole
animals. These sponges are actually carnivorous! They capture
small crustaceans with their spicules which act like Velcro when
they come in contact with the crustacean exoskeletons. Cells
then migrate around the helpless prey and digestion takes place
extracellularly.
Nourriture
!
Water flowing through sponges provides food and oxygen, as well as a
means for waste removal. This flow is actively generated by the beating
of flagella. The water movement through some sponges is aided by
ambient currents passing over raised excurrent openings. This moving
water creates an area of low pressure above the excurrent openings that
assists in drawing water out of the sponge. Sponges are capable of
regulating the amount of flow through their bodies by the constriction of
various openings. The volume of water passing through a sponge can
be enormous, up to 20,000 times its volume in a single 24 hour period.
In general, sponges feed by filtering bacteria from the water that passes
through them. Some sponges trap roughly 90 percent of all bacteria in
the water they filter. Other sponges, in particular hexatinellids, appear to
be less efficient at capturing bacteria and may specialize in feeding on
smaller bits of organic matter. Still other sponges harbor symbionts
such as green algae, dinoflagellates or cyanobacteria, from which they
also derive nutrients.