1,33 Mo
Collecting
sea urchins and their gametes.
Sea urchins (Paracentrotus lividus and Arbacia
lixula can be collected in the bay of Villefranche sur mer. Five
male or five female gonads are found inside the shell.
1,26 Mo
Male and female
sea urchin release sperm and egg in sea water.
Abundant sperm and millions of eggs are released in the sea water and
mix to produce zygote, embryos and larvae which are part of the plancton.
1,17 Mo
Thierry and Christian are starting a large culture of sea urchin embryos. Millions of synchronous embryos can be collected for reseach purpose in this way.
370 ko
Uppon adding a dilute sperm solution all eggs are synchronously fertilized and release thousands of cortical granules whose content assemble into a fertilization envelope.
400 ko
A single sperm fuses with the egg and triggers the elevation of a fertilization envelope.
From
sperm fusion to egg division.
The tip of the acrosomal process extended by the spermatozoid fuses with
the egg membrane. A calcium wave propagates. Nuclei of egg and sperm meet
because the sperm introduces a centrosome nucleating an aster of microtubules.
After the male and female pronuclei meet, mitosis and cleavage divide
the egg in two.
1,39 Mo
370 ko
This elevation of this proteinacious barrier participates in the block to the entry of multiple sperm (polyspermy).
530 ko
The nuclei of sperm and egg containing the male and female chromosomes meet using microtubules, and then fuse in the center of the egg.
1,40 Mo
Fertilization causes the egg to become a zygote dividing rapidly (every 30-60 minutes) forming a hollow ball of 1000 cells : the blastula, 5-7 hours after fertilization.
1,50 Mo
The ciliated epithelial cells forming the blastula secrete enzymes witch digest the fertilization envelope surrounding the blastula wich swims away using its ciliated cells.
800 ko
The larva skeleton
develops from small cells produced at the 16 cell stage.
A skeleton made of calcium crystals is secreted by small cells produced
at the 16 cell stage giving mesenchyme cells inside the embryo. These
cells form triradiate spicules which are berefringent in polarized light.
1,22 Mo
Spicules, the skeleton of the larvae are quasi-crystalline calcium carbonate structures wich are birefringent. They can be made iridescent when observed in polarized light and have shapes characteristic of the species.
400 ko
A digestive system forms from endoderm cells. The larvae feeds on small algae and grows.
2,1Mo
A small number of cells survive metamorphosis and the destruction of most larval tissues. The young urchin develops from these cells and moves using tubefeets.