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- The sea urchin is a
spiny and hard-shelled sea animal which lives on the rocky seafloor,
from shallow waters to great depths. These globular marine invertebrates
move very slowly along the seabed. There are about 700 different species
of sea urchins worldwide.
- Two common species of
sea urchins are the red (Strongylocentrotus franciscanus) and purple
(S. purpuratus), in shallow waters of California. Both species have been
implicated in the decline of kelp beds.
- In Japan, sea urchins
are protected rather than destroyed. Many sea urchins have venomous
spines. The biggest sea urchin is the red sea urchin (Strongylocentratus
franciscanus); having a test about 7 inches (18 cm) in diameter.
- Sea urchins eat plant
and animal matter, including kelp, decaying matter, algae, dead fish,
sponges, mussels, and barnacles.Sea urchins are eaten by snails, sea
otters, crabs, sunflower stars, some birds, fish (including wolf eels),
- Fertilization of sea
urchin is external. Female Sea Urchins release several million tiny,
jelly-coated eggs at a time. Eggs or sperm are released through five
gonophores. As they develop, the tiny larvae (called the pluteus, which
have bi-lateral symmetry) swim in the sea and are a component of
- It takes several
months for juvenile sea urchins to form. The time from fertilization to
a reproductive adult is from 2 to 5 years.
- Sea urchins are
creatures that live in oceans all over the world. Similar to sea stars,
sea urchins have a water vascular system. Their spherical shape is
typically small, ranging from about 3 cm to 10 cm in diameter, and their
body is covered with a spiny shell.
- A common place
to find a sea urchin is in coral reefs. Examples of where sea urchins
are very commonly found are on the reefs of Hawaii, of the Caribbean and
of Australia. Sea urchins have also been reported to cause erosion of
reefs in places such as the eastern Pacific, Kenya and the Red sea.
- So although sea
urchins are important to the survival of an ecosystem, they can also
become dangerous in great numbers. Other family members include the sea
cucumber, sea star and sand dollar.
- Unfertilized egg,
Fertilized egg, Two cell stage, Four cell stage , Eight cell stage,
Sixteen cell stage, Thirty two cell stage, Morula stage, Blastula stage,
Gastrula stage, Pluteus larval stage are the stages of Fertilization of
- Urchins are prized
for their edible gonads, known as uni in Japan. High quality uni can be
worth as much as $80 or more per pound. The fishery in Maine peaked in
1993 at around 40 million lbs. and employed over 1,800 people; by 2009
less than 5 million lbs. were harvested.
- 2010 Dock prices for
whole urchins exceeded $5/lb. during peak demand. Farming methods
include sea ranching, cage systems, and land based tank farms. Urchin
gonad bulking, holding for harvest on demand, and value added processing
are all ways to optimize a limited resource.
- The harmful effects
of sea urchins to the marine communities called for a reduction in their
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