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Choose a word or words from the box below to complete the following sentences. blood circulatory gills tissue capillaries countercurrent flow opposite Fish use specialized organs called (2.lls . to take in oxygen dissolved in water. Gills are large sheets of frilly Tiss Me filled with blood Fish systems pump blood in a single loop through a heart with two main chambers. is the movement of water against the flow of in the fish's gills. cartilage electrical lateral line sensory chimeras Holocephali muscular sharks Elasmobranchs. internal rays skates Members of phylum Chondrichthyes have skeletons made of . The two groups within phylum Chondrichthyes are the and the The Holocephali include also called ratfish. The Elasmobranchs include and While the cartilaginous fish as a group may be ancient, they have many advanced features. They have fertilization, and many species give birth to live : CHAPTER 25 Vertebrate Diversity. young. Fish can sense their prey's movements at a distance with a sensory system called the Many fish also have organs that detect the electrical currents made by contractions in other animals. These sensory organs are called 12 cells because they receive electrical signals. . Countercurrent Flow