Echinodermata+6th+Period

ECHINODERMATA The phylum of Echinodermata is the largest phylum to lack any freshwater or land organisms. It contains organisms such as sea stars, sea urchins, sea cucumbers, and sand dollars. ** CLASSES ** Phylums are divided into classes based on certain characteristics of the organisms in each class. The phylum Echinodermata happens to have 5 different classes: Criniodea, Asteroidea, Ophiuroidea, Echinoidea, and Holothuroidea. Crinoidea are sea lilies, Asteroidea are starfish, Ophiuroidea are brittle stars or snake stars, Echinoidea are sand dollars and sea urchins, and Holothuroidea are sea cucumbers.



** SYMMETRY **

There are 4 different types of symmetry an animal can have: No symmetry, Bilateral symmetry, Radial symmetry, and pentaradial symmetry. If an organism has no symmetry, it is not the same no matter which way you divide it. If an organism had bilateral symmetry, it can be divided down one midline and it will be the same on both sides. Radial symmetry is when you can divide the organism on any midline and it will be exactly the same on both sides. Pentaradial symmetry is when there are 5 different midlines that the organism can be divided down and still be symmetrical. Most Echinodermata have pentaradial symmetry, such as sea stars, though some other members of the phylum happen to have radial symmetry.



** CHARACTERISTICS ** Echinodermata have very unique characteristics. Five of the characteristics that they possess are tube feet, the fact that they are deuterostomes, the fact that they are coelomates, pentaradial symmetry, and a tissue-level of organization. **//TUBE FEET //** All Echinodermata have tube feet. Tube feet are connected to another trait that all echinoderms possess, a water vascular system. The water vascular system in Echinodermata is a series of water transporting canals that run throughout their bodies, ending in tube feet. Echinoderms can have hundreds of these tube feet, and by controlling their internal water pressure they can expand and contract their limbs, allowing for movement and mobility.



**//COELOMATES //** All organisms in kingdom animalia can be classified into three categories based on the presence of a body cavity. In animals, a body cavity is the space between the outer covering (skin) and the outer lining of the internal organs. An organism with a fully formed body is known as a coelomate, an organism with a partially formed body cavity is known as a pseudocoelomate, and an organism that lacks a body cavity is known as an acoelomate. All organisms in Echinodermata are coelomates, which means that they have a body cavity.



As discussed earlier, most Echinodermata have pentaradial symmetry. This means that they have five midlines that they can be divided down, and that each midline will result in two identical halves to the organism. This is very apparent in sea stars, for each midline goes through one of the 5 legs it has. Most, but not all, organisms in the phylum have this trait. The ones who don’t have pentaradial symmetry, however, have a form of symmetry known as radial symmetry. Organisms with radial symmetry can be divided down any midline and will still be identical in both halves. Examples of this are sea urchins and sea cucumbers.
 * // PENTARADIAL SYMMETRY //**



**//DEUTEROSTOMES //** All echinoderms are deuterostomes. The term deuterostome applies to a process that occurs during embryonic development. As a blastula, which is a hollow ball of cells, an organism can develop in two ways. Their blastopore (a small opening in the hollow ball of cells) can develop into a mouth, and then the side opposite can develop into an anus, or the blastopore can develop into an anus and then the other side can develop into a mouth. When an organism develops a mouth first, they are known as protostomes. When an organism develops an anus first, they are known as deuterostomes. Deuterostomes are known as more advanced evolutionarily, and all echinoderms are deuterostomes.

**//TISSUE LEVEL OF ORGANIZATION //** There are three different possible levels of organization in an organism. These levels are cellular, tissue, and organ organization. Cellular would be like a one celled organism. Tissues are made up of many cells, and so the next level of organization would be a tissue level of organization. When many different types of tissues work together they create organs, and animals with organ systems are normally considered to be the most complex organisms. Organisms in Echinodermata have a tissue-organ level of organization. They are made up of many cells and have an organ system made up of all the different tissues in the organism.

** EVOLUTIONARY ADVANTAGES ** Echinoderms are evolutionarily successful and prosperous in their environments for a number of reasons. Their combination of characteristics and abilities has allowed them to survive natural selection and continue on as a phylum. Their water vascular system allows them to move through the water efficiently and smoothly. It also helps them to get food for energy and it helps with respiration under water. Their ability to grow back their limbs should they be severed allows for survival even when a limb has been removed, and their pentaradial symmetry helps with streamlined movement and better all-around body functions for living in the ocean. They have an internal skeleton with flexible joints that allow for easy movement in the ocean. They are advanced as a phylum, for they are deuterostomes and coelomates with an organ system. Being a deuterostome is considered evolutionarily advanced, as with being a coelomate. Having that inner body cavity allows for better organization of an Echinoderm’s organs, and therefore being a coelomate is an evolutionary advantage. Having different kinds of tissue is also evolutionarily advanced, because when these tissues work together to create organs then the organism functions better as a whole. This is why Echinoderms have been able to survive and thrive over time. They have a unique combination of characteristics that allows them to thrive in their environment, and they have been able to survive natural selection. They have a evolutionarily advanced system (they are deuterostomes, coelomates, and have an organ level of organization) that has allowed for survival on their niche.




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