chapter 8 -Critical thinking

1. Hagfishes and lampreys are the only living representatives of a very ancient group. Why do you suppose there are still some of these jawless fishes around?
- The reason is that jawless fish are the earliest vertebrates of the class Agnatha, and their only living representatives are the cyclostomes- the lampreys and the hagfishes. Jawless fish still around today because they eat the dead or dying fish and other things that float on the bottom of the ocean. Their unusual feeding habits and slime-producing capabilities have led members of the scientific and popular media to dub the hagfish as the most "disgusting" of all sea creatures.

2. A deep-water shark, new to science, is collected for the first time. The specimen is studied in detail, but its stomach is empty. How could you get a rough idea of its feeding habits? The specimen is a female, and its reproductive tract is found to contain 20 eggs. Can you tell the type of development characteristics of this species?
- The cat shark species are found from 1988-2001. The cat shark species are opportunistic scavengers, with their main prey being fish and crustaceans. A “high intake” group received a given quantity of food twice a week; a “low intake” group received the same quantity of food only once a month. Cat shark feeds on deep water prey such as small fish, crustaceans, and cephalopods. The cat shark laid their eggs in huge and they have 20eggs beds up to 30 feet (10 meters) apart. Cat sharks are oviparous, producing eggs that develop and hatch outside the body of the female. Related species have been bred successfully in captivity.

3. Individuals of some species of bony fishes change sex, some to maintain more males than females, others more females than males. What are the advantages and disadvantages of each situation? Are there any advantages and disadvantages in having an equal number of males and females?
- in the biology theory , if there are more males than females, they will get more different of bony fishes, because female have more chance to mate with males and then have high production results. Also, they will choose the best gene male to production their generation and the next bony fish will be better than their parents generation. If there are more females than males, it will have low production results, because there has completion of the many females to mate the fewer males. Also, the gene to the next generation is not very good. If there are equal number of the both female and male, there will have the normal population on the next generation. Also, they will have not a lot of the gene on the generation.