Sea Stars
A student web page designed by Sheila Hollanders and Iona To


Anatomy:
Sea stars are radially symmetrical, and their arms are arranged around a central disk. Most species have five arms, however sun stars can have as many as 40 arms or more! Most sea stars are small usually measuring 12-24 cm across, but there are some species that can be very small or very large. For example, Pycnopodia, the many-rayed star of the Pacific Northwest can be as big as 1 meter across! The mouth of a sea star is found in the centre of the underside of the sea star (called the oral surface). Several rows of tube feet run from the mouth down each arm of the sea star. These rows of tube feet are guarded by movable spines that line the edges of the arms for protection. The back side of sea stars can be smooth, spiny, or slimy.

Movement:
Sea stars walk using their tube feet to move themselves along a surface. Their tube feet have suckers on the ends, which they use to attach themselves to rocks and to trap prey items. Sea stars that live on soft surfaces (such as sand) do not have suckers. These sea star uses their longer tube feet instead, to penetrate into the sand and other soft surfaces.

Feeding Habits:
Most sea stars are carnivores (which means that they eat other animals) that feed on gastropods, barnacles, sea anemones, sea snails, sea urchins, bivalves (shellfish) and some times even crabs, dead fish, and other sea stars. Pretty much any animal they can get their feet on! Instead of their food into their mouth as we do, sea stars instead flip their stomachs out through their mouth and digest their prey from the inside out. When the animal is completely digested the stomach is pulled back into the sea star's body.

Reproduction:
Sea stars are dioecious, meaning that the males and females are in separate individuals, and have as many as ten gonads (two at the end of each arm)!! Sea stars reproduce by free spawning which means the eggs and sperm are released into the water from the male and female at the same time. The eggs and sperm then drift off until they meet up with each other and fertilization occurs. Hundreds of thousands of larvae are released into the ocean during one breeding season, however a large portion of these do not survive. As sea star larvae float along through the plankton they are food to fish and other sea creatures.

Regeneration:
Sea stars have the remarkable ability to regrow their arms if they are damaged or eaten by predators. In fact, in some cases an entire sea star can be regenerated from just a single arm! However, this process is slow and it may take up to a year for a sea star's arm to grow back to its original size.


Three common sea star species of the Pacific Coast are:

Dermasterias imbricata:

Common name: Leather Sta

Alternate name: Garlic Star

Description:

The Leather Star is a slimy creature that can be up to 10 inches in size, most however are only 8 inches across. Leather stars are usually reddish brown in colour mixed with gray. Often times leather stars can be found with elements of purple between the red. This sea star has a strong garlic odour as its alternative name suggests.

Habitat and Distribution:

Leather stars live in rocky areas of the seashore from Alaska to California.

Other interesting facts:

Leather Stars cause an extreme response in the sea anemone, Red Stromphia. When the anemone feels the touch of a Leather Star, it immediately begins to sway back and forth until its base detaches from the sea floor. The anemone will "dance" through the water to distance itself from its enemy. Once it feels it is far enough away from the leather star, it will settle down on the sea floor once again.


Mediaster aequalias:

Common name: Vermilion Star
Alternate name: Equal-arm Star

Description:

Vermilion sea stars are bright red on their dorsal side (side facing the water) and are orange on the under side.

Habitat and distribution:

Equal-arm stars are found along the west coast of North America from Alaska down to California, on gravel, rocks, and sand in the low intertidal zone.


Pteraster tesselatus

Common name: Cushion Star
Alternate name: Slime Star

Description:

Cushion stars are usually 6 inches across. They are yellow to tan to gray in colour and can even be checkered sometimes.

Habitat and distribution:

These sea stars are found from the Bearing Sea down to California, usually resting on broken or solid rocks.

Other interesting facts:

To help protect itself from fish and other predators, the cushion star releases huge amounts of mucus.

click here for more about intertidal sea stars...


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