More Similar Than We Know
Echinoderms as a fascinating group of organisms that includes the sea pig, as pictured here. This organismA living individual made up of cells. allows parasites to live in its leathery yet translucent exterior, carries its respiratory organs in its butt, and is just downright strange. Echinoderms such as sea stars, sea urchins, and the unfortunate sea pig are more closely related to Chordates (a phylum including vertebrates) than to other invertebrates. In early stages of developmentThe process of growth and differentiation., chordates and echinoderms both create a digestive tract with two openings.
Spiny Skin & Special Symmetry
The term Echinoderm means spiny skinThe body’s largest organ, providing protection and regulation.. These organisms all have a tough skin with roughness. They also have a very particular respiratory systemThe organ system responsible for gas exchange (oxygen and carbon dioxide). called a waterThe universal solvent essential for life. vascular system. Echinoderms all have five-sided or pentamerous symmetry. This is a very specific type of radial symmetry common to the adult forms; larval forms are bilateral. You may already be familiar with these strange organisms like sea stars, brittle stars, sea pigs, and urchins. As you know, I like to remind you of extinct life forms; this is what is known as a sea lily or crinoids. These were like sea stars on top of a stalk. When they die, the sea star part would break off and the stalks would become fossilized. On the west side of Canandaigua Lake, near the physical location of FLCC, there are shale deposits with millions of the talk remnants. They look like stacks of lifesavers. I have some large rocks in a stone walkway at my house that have tons of these.
Horrifying Hunters
Let’s use the sea star as an example for anatomyThe study of the structure of the human body. of echinoderms. The arms of a sea star are called rays and in each ray is a digestive organ and a reproductive organ. The digestive glands are attached to two stomachs at the center of the sea star. One stomach is really for digestion and the other is a cardiac stomach that pulses, creating pressureThe force exerted by gases in the respiratory system, affecting airflow and gas exchange. differences to move water. The digestive stomach can be extruded from the mouthThe opening of the digestive tract where food enters and mastication begins., which is on the underside of the sea star. What they do is they find a shelled organism here and throw up their stomach and digestive enzymesProteins that speed up chemical reactions in the body. into the shell, digesting the clam in its own house. The sea star then takes back its stomach and recently digested meal. Horrifying for the clam.
Water for Blood
Echinoderms have what is called a water vascular system. They have an internal system of tubes, like our blood vessels, but they are not filled with blood, but the water from the environment. In this way, the organism floods its internal environment with water and exchanges gases between cellsThe basic structural and functional units of life. and the interstitial fluids. Water enters through an opening called the madreporite, on the opposite side of the mouth, circulates in the ring canal, then flows through radial canals in the ray of a sea star. This radial canal is connected to the tube feet that are basically water filled suckers. These tube feet are used for locomotionThe ability to move using coordinated muscle contractions.. You can see them here on an urchin, pulling the urchin along as they connect and disconnect with the substrate underneath him.
List of terms
- organism
- development
- skin
- respiratory system
- water
- anatomy
- pressure
- mouth
- enzymes
- cells
- locomotion