Cephalopod
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| Cephalopod |
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| Scientific Classification |
| Orders |
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Subclass: Nautiloidea
Subclass: Ammonoidea Subclass: Coleoidea |
Contents |
Introduction
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Anatomy
The Class Cephalopoda has the most developed form in phylum mollusca. It is divided into 3 parts of the body; head, trunk, and the limbs. Also they can be cut in halves equally. The sizes of cephalopoda are various, usually 1" to 7". They have small head with sharp and beak-like mouth. Mostly behind its mouth, radula, tooth tongue is placed. Using both mouth and radula, they grasp, tear and bite the prey.[1] However, class cephalopoda mean ‘head-footed’ by its tentacles and arms, the most noticeable structures. Tentacles looks like long arms but shorter than arms. On the surface of each arm, there are suckers to have enough strength to catch the prey. Members of orders sepiolida and teuthidea have eight arms and two tentacles while octopoda and vampyromorphida have only eight arms. The body is supported by its mantle or shell. Especially only nautilida has an external shell while others have internal ones. [2]
Digestive and Excretory system
All members of cephalopoda are carnivorous. When the arms and tentacles catch the prey, cephalopds put the food into the beak-like mouth getting help from tentacles and arms. Before swallowing, the food goes into the buccal cavity imidiately and then it goes to the digestive tracts. Sometimes they excreted the digestive juices to disassemble the connection between the flesh and the bone of the prey to digest it effectively. At first, it passes through the esophagus and crop. The food is stored at the crop a moment and goes directly to the stomach and be broken down. In caecum, the most of digestion happens and the nutrients are absorbed. [3]
The excretion in cephalopods occurs by a pair of nephridia which has tubular looks. From the coelom, it gathers all fluids in its body and filters. Also it exchanges substances like salt with body tissues. The wastes are released into mantle cavity and finally excreted outside by pore. [4]
Locomotion
To move in water, cephalopods need a special structure that helps their locomotion. Order octopoids use their arms to walk on the sea floor, sepioids and teuthoids owns lateral fins to propel their body to move. However, the most common way cephalopods move is jet propulsion. [5] They are pumping water into the gills and through out the siphons or funnel called hyponome. Oxgenated water comes into the cephalopods' gills and provides oxgen all over the bodies. After giving oxgen, the water then expelled through the hyponome by muscular contraction. When water is expelled, they get energy to move to the opposite direction that the water went out. [6]
Circulatory and Respiratory system
Class cephalopoda has closed circulatory system which the blood is contained within vessels. A muscular enlarged portion of a vein that forces the blood into the gills is called branchial heart and cephalopods have two of it also called gill heart. [7] Their heart contribute in providing oxgen over the bodies from oxgenated water by contraction. Moreover they use hemocyanin, similar to hemoglobin but bluish protein, contains copper, and carries oxgen.
[8]
For respiratory system, the most important organ is gill. The outside of the gill called mantle cavity, receives the oxgenated water. After they get the water, mantle contracts itself and forces the water to the entire body to provide oxgen. Unusally they get the oxgen from the oxgenated water received by the gills.
Nervous system and Senses
Cephalopods have the most developed and complex nervous system among the all invertebrates. They have groups of ganglias and form a brain. The brain is seperated into parts that each of them controls specific functions like the way vertebrate do.
Cephalopoda not only have advanced nervous system but also great senses. Especially, they have good vision to detect the prey or predators. For example, common octopus can determine the brightness, size, shape, and horizontal or vertical orientation of objects. Although they can detect those well, but poor at deciding colors. According to Hanlon and Messenger 1996, most of cephalopods are blind in colors. Moreover, they have only one pigment using in vision while humans have three. [9] For structure of their eyes, they have square-shaped pupils and change its shape of pupil to narrow rectangle by the amount of lights. To get the image, they receive lights through the pupils and focused by lens.
Reproduction
Class cephalopoda are gonochoric that they have seperation in sexes. The females have only one oviduct and the males produce spermatophore. There are many ways that they transfer the spermatophore to the females. Most of species, they have an arm called hectocotylus is used to transfer spermatophore to the females. Then the spermatophore goes into the oviduct and get fertilized.
During the courtship between cephalopods, there might be color changes or body movements, and sometimes both of them happen. [10] The male changes his color into the brightest color as bright as he can and if the female becomes pale, it means that she accepts him. However, she remains in her color, it represents that she recognizes it as a dangerous situation to her.
Also most of them are semelparous that they lay eggs a lot at one time and die, but nautiloidea is exception. Nautiloidea lays eggs in each time and lives long.
Uniquely cephalopods have no larval stage to grow up. They just grow up directly in the image of adults. [11]
Ecology
The cephalopods are absolutely marine animals. They live in open sea freely. (Porch, Batdorf, p470) At the Baltic Sea, no cephalopods can be observed because of low salinities. However, they are found in Suez Canal where the salinities are much higher than the oceans. [12] This shows that concentration for salinities affects the habitat for cephalopods.
As they live in open sea which is a dangerous place to survive, they own some defense features. Some speices can change their color to fit in the environment.
Other
Gallery
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References
- Class Cephalopoda Kristen Wheeler, Daphne G. Fautin, Animal Diversity Web, 2001.
- The anatomy of swimming in cephalopods Carl Howard, jrscience.wcp.muohio.edu, 2003.
- Cephalopod wikipedia.
- Cephalopod vision Dr. James Wood, Kelsie Jackson, publisher, date.
- Cephalopod(class of mollusca) encyclopedia of Britannica.
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