Cyclostomi facts for kids
Quick facts for kids Cyclostomes |
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| Sea lamprey from Sweden | |
Scientific classification  |
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| Kingdom: | Animalia |
| Phylum: | Chordata |
| Superclass: | Agnatha |
| Superclass: | Cyclostomi Duméril, 1806 |
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Cyclostomes are a fascinating group of vertebrates that includes two types of living jawless fish: lampreys and hagfishes. The name "Cyclostomi" comes from ancient Greek words meaning "circular mouth," which perfectly describes their unique mouths!
These animals don't have jaws like most fish you know. Instead, they have round mouths with special, tough structures that work like teeth. Their gill arches, which help them breathe, are located inside their bodies, unlike the external gills of many other fish.
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Amazing Jawless Fish: Cyclostomes
What Are Cyclostomes?
Cyclostomes are a very old group of animals. They are special because they are the only living vertebrates that do not have jaws. This means they are quite different from sharks, tuna, or even humans, who all have jaws.
There are two main groups of cyclostomes alive today:
- Hagfishes: These are often called "slime eels" because they can produce a lot of protective slime.
- Lampreys: These fish have a distinctive funnel-like mouth.
Both hagfishes and lampreys have soft, scaleless bodies. They are important for understanding how vertebrates, including humans, first evolved.
How Scientists Study Their Family Tree
For a long time, scientists wondered how lampreys and hagfishes were related to each other and to other vertebrates. Some thought lampreys were more closely related to jawed fish than to hagfishes. Others believed lampreys and hagfishes were closer relatives, forming a single group called Cyclostomi.
Today, most studies that look at the DNA and genes of these animals suggest that lampreys and hagfishes are indeed close relatives. This means they likely share a common ancestor that was also jawless. Scientists use many clues, like how their bodies are built and their genetic information, to figure out these ancient family trees.
Some ancient jawless fish, like conodonts and anaspids, might also be related to cyclostomes. These ancient fish sometimes had hard, mineralized parts, like armor or teeth. This suggests that the very first vertebrates might have had these hard parts, but lampreys and hagfishes later lost them over millions of years.
Unique Features of Lampreys and Hagfishes
Lampreys and hagfishes share some interesting traits, but they also have clear differences.
Life Cycle and Development
Hagfishes develop directly from an egg into a small hagfish. They don't have a larval stage. Lampreys, however, have a more complex life cycle. They start as tiny larvae called ammocoetes. These larvae live in freshwater and filter tiny bits of food from the water. Ammocoetes have a special organ called an endostyle, which helps them filter feed. This endostyle later changes into the thyroid gland when the lamprey grows up. After a few years, the ammocoetes change into their adult form through a process called metamorphosis.
Their Special Mouths and "Teeth"
Both hagfishes and adult lampreys have unique mouths without jaws.
- Lampreys have a round, suction-cup-like mouth. Inside, they have tough, horny "teeth" on a tongue-like structure that helps them latch onto prey.
- Hagfishes also have horny "teeth." These teeth are on plates that slide back and forth, like a conveyor belt, to help them scrape food. They also have a special tooth hanging from the roof of their mouth.
Other Cool Differences
- Reproductive Organs: Both hagfishes and lampreys have only one gonad (reproductive organ). In hagfishes, one of their two original gonads disappears as they grow. In lampreys, the two gonads fuse together to form one.
- Internal Organs: Unlike many other vertebrates, hagfishes and lampreys do not have a thymus or a spleen. They also lack myelin, which is a fatty layer that helps nerve signals travel fast in other animals.
- Senses: Both groups have only one nostril and one olfactory organ (for smell). Their inner ears are also simpler than those of jawed vertebrates. Lampreys have two semicircular canals in each ear, while hagfishes have only one. Jawed vertebrates usually have three.
- Blood: Hagfishes have blood that is very similar to seawater in its saltiness. Lampreys, however, can control the salt levels in their blood, much like marine fish do. Scientists think hagfish ancestors might have lived in freshwater long ago and then adapted to saltwater over a very long time.
- Intestines: Lampreys have a special fold in their intestine called a typhlosole. This fold increases the surface area for absorbing nutrients, similar to a spiral valve found in some other fish. Hagfishes have a simpler, zigzag pattern in their intestines.
