Stars of the Sea, Sea Stars also known as Starfish

from Provinceown MA on Cape Cod

Starfish, which are neither a star nor a fish are commonly called Sea Stars in other parts of the world, but here in the states we insist on calling them Star Fish. My mother always said, "Felicia, what are these things...we should look them up on the inner-net." She would say this often at the store when we would string the beads by hand for our Provincetown star fish ornaments. Capes Treasures has uncovered some interesting Starfish facts to share with you. 10/12 finish

There are over 1,800 known species of starfish, and they live in all of the world's oceans. The most diversified collections exist in the tropical-temperate regions around Australia, the tropical East Pacific, and the cold-temperate waters of the North Pacific. In these seas starfish can be found in tropical coral reefs, kelp forests, and deep on the ocean floor. Relatively rare North of Massachusetts, they are mostly shallow water dwellers although some have been found in more than 500 fathoms of water. The best time to hunt for Starfish is at low tide, in the crannies and crevices of tide pools, under or along the sides of rocks and empty shells. They must maintain a delicate internal balance and cannot survive in freshwater environments.

Starfish are composed of a central disc from which arms radiate out in pentaradial symmetry, with five being the most common number of arms. Due to autotomy (the ability to cast off a body part) and abnormality of subsequent regenerations,some starfish can be found with six, seven, or eight arms. The mouth is located on the underside of the animal on the oral or ventral surface. The spiny upper (aboral) surface is where both the anus and the madreporite are located. The madreporite is a small white spot, usually observable to the naked eye, located off center from the central disc. It acts as a filter and feeds into the Starfish's water vascular system to allow the creature to move. Many starfish have dense rows of spines on their exterior surface that serve as a means of protection, surrounding these spines are tiny white objects called pedicellariae which prevent encrusting organisms from invading and colonizing the starfish. Across each arm is a radial canal which has tooth-like structures called ampullae and brightly colored pustules , mottles, or spots that act as camouflage or warning coloration. The starfish is unable to hear and can only register the differences of light and dark with a simple photoreceptor eyespot located at the end of each arm.

The body cavity contains the vascular system that operates the tube feet, and the circulatory (hemal) system. Hemal channels form rings around the mouth on the top of the starfish around the digestive system and a portion of the body cavity called the axial sinus connects the rings. Each arm has hemal channels running next to the gonads.

Starfish are carnivores, and prey on mollusks (oysters, quahogs, and mussels) and crustaceans (barnacles, crabs, and shrimp). Two stomaches are used in the digestion of food. A starfish wraps it's arms around it's chosen prey and pries open the shell by wearing out the adductor muscle. It just needs a small opening to be able to insert it's cardiac stomach (from the center of the body) into the shell to engulf and ingest the animal. The cardiac stomach is then retracted back into the starfish's body and the partially digested food is transfered into the pyloric stomach with final digestion occurring in the intestine. Waste is either expelled through the anus on the aboral side of the animal or is excreted through the mouth.

Some starfish live several weeks without food under artificial conditions, possibly because they are able to receive some nutrients form organic matter dissolved in seawater.

Lacking a centralized brain, the starfish does have a complex nervous system composed of interlacing nerves called a nerve plexus, which lies within and below the skin. The esophagus is surrounded by nerve rings and radial nerves that run parallel with the branches of the water vascular system. These nerve rings coordinate the starfishe's balance and directional systems. They are sensitive to touch, light, temperature, orientation, and status of water surrounding them.

Starfish move using a water vascular system with water entering through the madreporite. It is circulated from the stone canal to the ring canal and then to the radial canals which propel water to the ampllae and provide suction to the tube feet. The tube feet latch onto surfaces and move the starfish in a wave like fashion, one body section attaching as another releases. Most starfish cannot move rapidly but some burrowing species are able to swiftly glide across the ocean floor with the aid of specially adapted pointed tube feet.

Starfish are either male or female, and are capable of A sexual, and sexual reproduction. Using environmental clues, starfish coordinate their mating. A female will release several million eggs over the course of two hours, the average diameter being just .16-.19 mm. After being fertilized by gametes released by the male, the eggs form into hollow balls, called the bastulas. These balls are cilliated ( with small hair-like cells) for swimming. After 24 hours, a deep groove leading to the gastrula develops. The starfish develops a bipinnaria larva with ciliated bands running about it's periphery. After several weeks, the larva take a more elaborate form with longer projecting arms and a gut with cilia inside to inhale and transport food (plankton) to the large round stomach situated on the ventral surface. Starfish undergo a metamorphosis from bilateral symmetry to radial symmetry in two months, and is ready for reproduction after about one year. Asexual reproduction is achieved when an arm of the animal is removed, (with some of the central disc attached), and a new independent starfish is formed. Before this ability came to be understood, fisherman whose haul of shellfish were greatly diminished by the relentless predatory starfish, would remove them from their nets and chop the animals in half, returning them back to the sea. Finally, fisherman started watching the Discovery Channel and stopped accidentally doubling the number of starfish.