halfway through essssay

When somoneone hears the word starfish, usually they automatically think of a five armed sea creature that looks rather lifeless. However, these asteroids are more complex than most would realize and play an important role in the ecosystem, at least, most of the time. In the ocean, there are many different kinds of starfish with different physical attributes and behaviors. Despite their diversity, they all reproduce,develop and grow within their habitat and just like any other living organism, they face dangers and can only live so long.

They live in just about any habitat in the ocean; such as tidal pools, rocky shores, sea grass and kelp beds, beneath rock rubble, on coral reefs, sand, and mud. They are seafloor predators. They have certain attributes which allow them to withhold rough conditions, such as their suctions which allow them to stay stuck in seabeds or close to shore despite the crashing waves. As for diversity, there are roughly 1500 different species in the Asteroidea class(CITE). Considering there are so many different species, there are two starfish in which I will go into further detail about. The Asterias rubens and the crown-of-thorns starfish Acanthaster planci are both very different. The Asterias rubens are what most consider the common starfish, and the Acanthaster planci is a very different, unique starfish that most wouldn’t even realize is a starfish.

Physically, most starfish have five arms radiating off a central disk, such as the Asterias rubens. On the other hand, some star fish may have up to fourty arms, while the crown-of-thorns as between 10-20 arms. Starfish come in a vast variety of colors which include bright red, cobalt blue, yellows, and the familiar orange-brown (http://science.jrank.org/pages/6450/Starfish.html). For size there have been sea stars as small as 2cm in diameter yet as big as one meter in diameter.
On average, starfish are between 12 and 24 cm in diameter. They have a very rough surface, some with short bumps and ridges, while others may have thorn-like spikes, such as the crown-of-thorns.

Another neat thing about starfish is that they can produce sexually and asexually. Although they are known to be able to regenerate arms if necessary, seven species (that tend to be very small) are known to willingly pinch off one or more arms that then redevelop a complete new disc and arms.

However, most asteroids reproduce sexually. Each arm holds a pair of gonads that become almost filled with eggs or sperm during the time of breeding. Most species are broadcast spawners, which means that the eggs and sperm are released into the water column to be fertilized. To increase the chances of fertilization, sea stars come together when they are ready to spawn. The crown-of-thorns sea star, for instance, releases a potent chemical into the water column to attract the opposite sex. As for the Asterias Rubens, the female produces small eggs that are released into the sea and fertilized externally to develop as planktotrophic larvae. This type of reproductive strategy is known as indirect-development.

Some females hold their fertilized eggs in a brood space either under the arm, in the stomach, or keep them warm in the gonads. If they are kept in the stomach or gonads, they develop within and escape through small openings the female's body wall called gonopores.