jawless fish

features of jawless fish

Jawless fish are missing the following parts: 1. Jaws. 2. Paired fins. 3. A stomach. Characteristics they do have include: 1. A notochord, both in larvae and adults. Recall a notochord is a support rod that runs along the back of the fish. 2. Seven or more paired gill pouches. These organs take dissolved oxygen from water. 3. The branchial arches, a series of arches that support the gills of aquatic amphibians and fishes. They lie close to the bodys surface. 4. A light sensitive pineal eye, an eye-like structure that can detect light. 5. A cartilaginous skeleton, a skeleton made of a flexible rubber-like supportive material called cartilage. This is similar to the skeleton of cartilaginous fish, which includes sharks and rays. 6. A heart with two chambers. 7. Reproduction using external fertilization. 8. They are ectothermic. This means that their internal temperature depends on the temperature of their envi- ronment.

classification of jawless fish

Most scientists agree that the jawless fish are part of the the superclass Agnatha. They belong to the phylum Chordata, subphylum Vertebrata. There are two living groups of jawless fish, with about 100 species in total: lampreys and hagfish ( Figure 1.1). Although hagfish belong to the subphylum Vertebrata, they do not technically have vertebrae (though they do have a skull), whereas lampreys do have vertebrae. For this reason, scientists still disagree on the classification of jawless fish. A hagfish.

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jawless fish

What defines a jawless fish? You can probably guess. A jawless fish is a fish without a jaw. But there are other features that are shared by this class of organisms. Why would such an organism evolve? These fish were the first vertebrates to evolve. Logically, this makes sense, in that the vertebral column would evolve first, with the more complex jaw bones evolving later. The early jawless fish are thought to have relied on filter feeding to capture their food, and most likely would have sucked water and debris from the seafloor into their mouth, releasing water and waste out of their gills. As other sea life evolved, these jawless fish began to feed on other fish species, and are now considered a pest in their habitat. Lampreys have no natural predators.

instructional diagrams

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questions

jawless fish were the first fish to evolve.

-->  a. true

b. false

both groups of jawless fish have a notochord.

-->  a. true

b. false

jawless fish are missing

a) jaws.

b) paired fins.

c) a stomach

-->  d) all of the above

the skeleton of the jawless fish is made of

a) bone.

-->  b) cartilage.

c) rubber.

d) bone and cartilage.

characteristics of lampreys include

-->  a) a huge sucker lined with teeth.

b) a skull but no vertebrae.

c) internal fertilization.

d) all of the above

characteristics of hagfish include

a) a huge sucker lined with teeth.

b) a internal fertilization.

-->  c) a skull but no vertebrae.

d) all of the above

which statement is associated with jawless fish?

a) they have a series of branchial arches that support the gills.

b) they have an eye-like structure that can detect light.

c) they have at least seven pairs of gill pouches that take dissolved oxygen from water.

-->  d) all of the above are associated with jawless fish.

diagram questions

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