Chapter 7: Non-Bony Fish

Classification

Kingdom Animalia
Phylum Chordata
Class Agnatha - Jawless Fishes
Chondrichthyes - Sharks and Rays
Order Agnatha
Petromyzontiformes - Lampreys
Myxiniformes - Hagfish

Chondrichthyes
Rajiformes - skates and rays
Squatiniformes - angelfish sharks
Pristiophoriformes - sawfish sharks
Squaliformes - dogfish sharks
Carcharhiniformes - ground sharks
Lamniformes - mackerel sharks
Orectolobiformes- carpet sharks
Heterodontiformes -bullhead sharks
Hexanchiformes - frilled and cow sharks

Interactive journey through the shark classification

HagfishClass Agnatha (Jawless Fishes)

When you first look at a hagfish, you maybe more likely to think its a worm of some sort. They have no eyes, no jaws, no fins and nothing that resembles a modern fish. Yet fish they are, some of the most primitive fish on Earth. They can be found in both the Atlantic and Pacific oceans, where they live at depths of 100 to 3,150 feet. They will often play the role of decomposer and dependent on their sense of smell to find food. Hagfish can also invade the bodies of sick fish by entering through their mouths and settling in their stomachs.Once logged inside, they can death their hosts from the inside out. Hagfish are also known as slime hags because of their ability to produce copious amounts of slime. This slime protects them from the digestive juices of their hosts. The slime also is a great deterant for potential predators. Click here to see serveral YouTube videos of hagfish using their slime to defend themselves. (Image from: pbs.org) lamprey

Lampreys are parasites. They attach themselves to fishes, latch on with their teeth, and secrete an anticoagulant into their hosts blood stream. Just like a leech or a mosquito, this keeps the fish's blood from clotting and allows a lamprey to drink their victims blood. Sometimes a lamprey will kill its host, other times it will detach leaving its host wounded but alive. Much like salmon, adults spawn in freshwater. Young lampreys will make their way into saltwater as adults, returning only when they are ready to reproduce themselves. At least one species of lampreys have become landlocked in the Great Lakes where they have caused significant damage to the sport and commercial fishing industry. (Image from: pbs.org. )

Class Condrichthyes (Sharks and Rays)

spotted bat rayThe class condrichthyes includes all sharks and rays.To most untrained eyes sharks and rays look nothing alike. With the noticeable exception of ray's kite-like body and mouth underneath instead of in front of their body, sharks and rays are structurally very similar. All members of the class Condrichthyes have a skeleton made of cartilage rather than bone.  This is useful because cartilage is lighter and more flexible than bone.   Condrichthyes lack an air bladder, which means they have a natural tendency to sink. As such, most sharks have pectoral fins that are shaped and function much like airplane wings. Water moving over their fins, gives them lift. Ray's wings are nothing more than oversized pectoral fins, and also serve to provide lift while swimming.

Sharks and rays will have 5-7 gill slits instead of the one that their cousins the bony fish have. Almost all sharks and rays have a movable jaw and well developed teeth.  Sharks and rays have placoid, or hook-shaped scales that give them a rough and armor like skin.

Special ampullae of lorenziniAdaptations of Sharks and Rays 

Ampullae of Lorenzini - The AOL are tiny pores on the ventral side of a sharks snout.  These pores sense tiny electrical pulses that are created by the muscle movements of other fish.

Lateral Line - Similar (in some respects) to the ampullae of lorenzini, the lateral line is a row of pressure sensitive pores that run the length of the sharks body.  The lateral line allows the shark to orient to particle movement or sound.  It consists of structures called neuromasts which are located in canals that lie just below the surface of the skin or the scales.

Sharp Rough Skin - Sharks and rays also share the same kind of skin: instead of scales, they have small tooth-like spikes called denticles. The spikes can be so sharp, in fact, that ocean going cultures have long used shark skin as sandpaper.

Teeth Thanks to the novel and movie "Jaws." Sharks are know for their teeth, but no two shark species has exactly the same teeth. As such, teeth or bite marks can be used as an identifying characteristic of individual species. Those huge, triangular teeth familiar from Jaws have serrated edges that equip the white shark for cutting into a fare of seals, sea lions, porpoises, even sea turtles.  Other species will have teeth that are more pointed and spear-like which are much better adapted for grabbing than for cutting. Not all sharks have teeth. In fact there are several shark species (like the basking shark pictured at the top of this page) that are strictly filter feeders.

Shark and Ray Diversity

There are several hundred shark and ray species that inhabit all of the oceans habitats. Check out some of the links to learn about a variety of shark and ray species.blue shark caught in a net

Sharks are in Trouble

Sharks are especially vulnerable to habitat destruction and fishing pressure because they have slow rates of maturation and low reproductive rates. Sharks are unusually long lived and give birth to a relatively small number of young when compared to other types of fish. Many species breed only every other year and have gestational periods as long as thirteen months.

Sharks are often caught as bi catch by tuna fishermen using long lines or drift nets. However, for the last 30 years sharks have been increasingly targeted for their fins.  Sharks can be eaten (some are very tasty), but most are taken only for their fins.  Shark fin soup is a very popular (and very expensive) dish served in many Asian countries.

Questions to Research:

  1. With no jaws, explain how lampreys and hagfish eat.

  2. Draw a simple sketch of a shark and label all of its fins.

  3. Visit any of the sites in the shark and ray diversity section.  Pick your favorite (the one that is most interesting to you). Describe your favorite shark or ray and explain why it interests you.

  4. Anatomically speaking sharks and rays are really more alike than they are different.  However, they use their bodies very differently.  Watch a video of a manta ray swimming and a hammerhead shark swimming.  Describe the difference.

  5. Examine the picture to the right.  Then go to the Shark-O-Matic to identify what species of shark this is.

  6. To check your answer in #4, click here to watch a video of this shark species. After watching the video, how would you describe this sharks feeding strategy?

  7. Whale sharks and basking sharks are the largest of the sharks.  Yet they feed on the smallest of prey (plankton.) Watch either video and describe in your own words what this looks like.  

  8. We often consider salmon sharks a "local species" in South central Alaska.  TOPP has been actively tagging and tracking salmon sharks for the last five years.  Go to the interactive map and explain where salmon sharks go after a summer spent in Prince William Sound.

  9. Explain how the Ampullae of Lorenzini and the lateral line help sharks locate prey.

  10. In 2010 about 60 people were killed world-wide by sharks. In the same year, estimates are that people killed 73 million sharks. The hunter is now the hunted. Use the two following links to do a little research, then explain why the survival of sharks is increasingly under threat.