Research Paper Example
Water covers about seventy percent of the Earth. A large portion of that amount is the immense oceans. There are lots of different creatures that live in these oceans that surround us. From sharks to whales, sea rays to fish, sea otters to penguins, seaweed to coral reefs, all have a variety of characteristics and a unique way of living. One that stands out is the sea star. This animal has interesting methods of movement, eating and surviving the dangers of the sea.
Sea star or starfish are Echinoderms, which is a Greek work meaning "hedgehog" and "skin" (Sayre, 1996). The subphylum is Stelleroidea, which has two classes, Asteroidea and Ophiuroidea. Asteroidea includes sea stars. Ophiuroidea includes the Brittle and Basket Stars. The difference between these two classes is the way the arms of the sea star are attached to their bodies. The sea star's arms are connected together to their body's central disk. Brittle and Basket Stars have a central disk, which is connected to their arms, but their arms aren't connected together (Bird, 2012).
Sea stars can be found in various habitats. They will cluster on rocky beaches, middle intertidal in tide pools until the tide rises again, and lower intertidal where seaweed, anemones and sea slugs are found (Sayre, 1996). Sea stars are also found in the epipelagic zone or the euphotic zone, which is zero to two hundred meters. In this area there is sunlight and photosynthesis occurs (Day, 1999).
Sea stars have an intricate body. When sea stars are born they are bilaterally symmetrical, which is when the left and right side are identical. As they mature they become radially symmetrical, when like appendages branch out of a central area. Their skin is spiny (Amaral, 2012). They can be found in different colors and different numbers of arms (Knight, 2008). Sea stars don't have eyes or brains (Sayre, 1996). Sea stars have
| Fig. 1 |
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| This is a close up picture of what the top of a Pycnopodia helianthoides looks like. The pinchers, pedicellariae, derma gills and spines are visible (Shimek, 2012) | |
calcareous plates that are linked together by muscle and tissue instead of spines (
Columbia, 2012). There are nervous cells within the sea star. They have large fine nerves that help the sea star move around on the sea floor (Shimek, 2012). On the top of their body there are pinchers called pedicellania (see Figure 1) (Bird, 2012). These pick off any barnacles or parasites off of their bodies. Also on the top part, they have dermal gills. This is where gases are exchanged. Dermal gills are slimy, skinny, finger like things on the top of the sea star, which are covered with tissue that can enter or exit the body by cilia (Shimek, 2012).
| Fig. 2 |
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| These are the tube feet on the bottom of the sea star's arms (Amaral, 2011). | |
On
top of the sea star there is a single colored circle, this is the madreporite. It has very small holes that filters the water as it enters and exits the sea star's body (Bird, 2012). At the tip of each arm there are eyespots (Columbia, 2012). The eyespots are sensitive to light. The specific type of sea star will depend on whether they prefer light or no light (Amaral, 2012). Around the tips of the arms there are tube feet (see Figure 2) that detect sound, smell and chemicals in the water (Sayre, 1996). On the
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