Cephalopod Respiration
Being aquatic animals, cephalopods respire using gills to filter oxygen out of the water and into their bodies. In cephalopods, the gills are attached to the mantle, which covers the visceral mass of mollusks. On each gill, there is a branchial heart attached at the base that pumps blood to the gills. The rhythmic pumping of these hearts causes the mantle to expand and contract, which results in the surrounding water flowing through the gills, allowing for gas exchange to take place and bring oxygen into the blood which will soon be pumped throughout the entire body (1).
The gills in cephalopods are designed to bring in as much air as possible. On each gill, there is a central axis with a row of lamellae on each side. Lamellae are thin, plate-like structures with open space between. In cephalopod gills, the lamellae are folded together, leaving more space on the gills for lamellae to occupy. With all these lamellae, there is a lot of surface area for the gills to make contact with the surrounding seawater. This efficient means of respiring allows for more oxygen to enter the body (2). Shown is a diagram of a gill. It is displaying the various structures that are important in the process of obtaining oxygen from the water, like the blood vessels and the lamellae.
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Pictured is the inside of a squid. The gills are the two long, grayish regions starting near the middle of the squid.
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Evolution
Cephalopods are much more complex than their fellow mollusks, with a closed circulatory system and having developed appendages in the form of tentacles. Also, they have developed a sophisticated eye and an advanced defense system, using ink to repel possible predators and cloud its escape. Earlier cephalopods must have faced multiple environmental pressures that other mollusks did not have to endure for all of these different morphological changes to occur over millions of years, but these changes resulted in cephalopods being some of the most sophisticated invertebrate animals in our biological world.
(1) Voss, Gilbert L. "Cephalopod - Form and Function." Encyclopedia Britannica Online. Encyclopedia Britannica, 9 May 2016. Web. 15 June 2016.
(2) Young, Richard E., and Michael Vecchione. "Cephalopod Gills."Cephalopod Gills. Tree of Life Web Project, 2008. Web. 15 June 2016.
(2) Young, Richard E., and Michael Vecchione. "Cephalopod Gills."Cephalopod Gills. Tree of Life Web Project, 2008. Web. 15 June 2016.