The symbiotic relationship is commensalism because the tiny fish gets a place to hide while the sea urchin is unaffected.

yes they do.

http://www.enchantedlearning.com/subjects/invertebrates/echinoderm/Seaurchin.shtml

Yes, they use a gas exchange (oxygen in and carbon dioxide out) taking place by diffusion across cell membranes of the tube feet.

Seahorses are fish; therefore, like all vertebrates, they have bilateral symmetry. This means they have symmetry across one plane (known as the sagittal plane, and directly down the centre of their body), which means one side of their body approximately mirrors the other side.

a sea sponge,well it depends what kind of sea sponge.a soft sea sponge can feel like wet pasta.a hard but squishable sea sponge will feel lumpyer.

-They produce a large amount of gametes

-They synchronize spawning so there are both sperm and eggs present at the same time

-Males usually spawn upstream so sperm gets carried to eggs

-Eggs adhere to the spines of the female urchin to keep them from floating away to make it easier for sperm to reach them

Nope. They are nekton because they actively swim and catch their food.

Echinoderms.

no, mammals are grouped together because they all posses hair, lungs and mammary glands (hence the name) to produce milk, and a few other features. the urchin does not posses any of these quality's and therefore is not a mammal

they have a lot more than 2

The most dangerous fish in the ocean is the piranha.

The piranha is a freshwater fish for Christ's sake!

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There's no such thing as one "most dangerous fish."

In venomous fish, the stonefish stands above all. Its spines pack a poison that can kill a human who steps on it, and the thing looks like a rock so you're likely to.

In predatory fish, there are a lot of contenders but I'll have to go with the shortfin mako shark, which is a seriously predatory animal.

Those are both marine animals. In freshwater fish, I give the nod not to the piranha--a fish not considered the most dangerous even in the Amazon River basin where it lives (people there consider the candiru, a catfish known for lodging itself in people's urethras, the most dangerous fish in the Amazon) but to one of two pangasiid catfish, the Paroon shark (p. sanitwongsei) or the Mekong catfish (p. gigas). These are huge fish--the Paroon shark grows to 10 feet in length and the Mekong catfish is larger--that are renowned for eating dogs and for tearing the guts out of fishermen with the spines in their pectoral fins.

Sea urchins eat very slowly but like many other animals, they eat on a daily basis. A sea urchin's diet consists of things like algae and seaweed. If this food is not available, they will eat things like dead animals and sponges.

The Painted Cave located on the Channel Island of Santa Cruz is home to many marine animals. Sea anemones and sponges normally brightly colored near the entrance to the cave will lose their color in the dark sunless reaches. Sea Lions also make their home on exposed ledges in the cave most of the year.

The classification of a Sea Urchin is Echinoidea

Soooo easy! Very peaceful animals that make fantastic pets. Everyone should have a seahorse!

Yes, In fact, A female sea urchin can lay up to 500 million eggs in her lifetime. These eggs are released out into the sea. A male sea urchin releases billions of sperm cells. When the egg and sperm meet, the baby sea urchin floats around until it matures.

• Sea star or starfish (Asteroidea)
• Brittle stars, basket stars, serpent stars (Ophiuroidea)
• Sea urchins, heart urchins and sanddollars (Echinoidea)
• Holothurians or sea cucumbers (Holothuroidea)
• Feather stars and sea lilies (Crinoidea).

So that the sea urchin can protect itself from is enemies, it also has venomous spines. They also use their spines to kill other sea ceatures, so they can eat them.

Sea stars are in the phylum Echinodermata and the subphylum Asterozoa.

No, atually they live in massive groups, searching for kelp and other sea grasses to munch on. A large mass of urchins can clear massive kelp forests in a short amount of time. Most urchin groups live in shallows, but some species prefer deeper waters.

dolphin