Ancient Creature of the Deep
To compare and classify a "living fossil," the coelacanth, in
relation to a moray eel and a bull shark.
- copy of the "Fish Anatomy" student handout
- Access to Internet and print resources for research
Review with students the meaning of the phrase "living fossil" (an organism with a basic body design that has remained unchanged for millions of years). Tell students that they will be comparing a living fossil, the coelacanth, with moray eels and bull sharks.
Organize students into groups and provide each group with a copy of the "Fish Anatomy" student handout.
Review with students the descriptions of fish anatomical structures on the student handout. Explain that these descriptions only represent a few of the different features of fishes.
Have students use additional resources to find more information about coelacanths, eels, and sharks. Ask students to research the skeletal types of each fish, its body covering, how the fish stays buoyant, and whether it bears live young. Then have them draw and label the body parts of each fish.
After students label all the fish body parts, review their answers (see Activity Answer).
Ask students if they think the coelacanth is more closely related to the eel or the shark, and have them explain their reasoning. List the reasons supporting each choice on the board. Then have a discussion to try to reach a consensus.
As an extension, have students research the characteristics of other living fossils, such as the horseshoe crab or the Ginkgo biloba tree. What makes these organisms distinctive? What might have enabled them to remain unchanged for so long?
A fish is an animal in the phylum Chordata and the sub-phylum Vertebrata. Most are covered in protective scales. Fish have fins, and most have swim bladders. The coelacanth has all these characteristics and is thus classified as a fish. The coelacanth is a unique fish because it has an extra lobe in its tail, paired lobe fins that move like our arms and legs, an incompletely developed vertebral column, and an intercranial joint that allows it to lift the front part of its head to feed.
The coelacanth and the eel are more closely related than the coelacanth and the shark. The coelacanth and the eel belong to the class Osteichthyes, the bony fishes. Bony fishes, as their name implies, have a bony skeleton. The shark is a cartilaginous fish (class Chondrichthyes). Cartilaginous fishes have a skeleton made of tough, flexible connective tissue. Most fish species are bony fishes. The class of bony fishes includes:
Subclass Sarcopterygii (fleshy-finned fishes): includes the coelacanth and a few species of lungfish.
Subclass Actinopterygii (ray-finned fishes): includes all other living bony fishes, such as salmon, trout, cod, eel, anchovies, and herring.
Here are some other comparisons:
Scales: Shark skin is covered by a layer of small tooth-like structures called dermal denticles. The denticles make the skin feel smooth when rubbed from head to tail and rough when rubbed the other way. Most bony fishes have large, overlapping scales. Eels have thick, non-scaly skin covered with more mucus than other fishes. Coelacanths have scales.
Buoyancy: Most bony fishes have gas-filled swim bladders that keep them afloat. The shark has an oily liver that serves the same purpose. The coelacanth has a fat-filled swim bladder.
Reproduction: Most sharks give birth to live young, but some deposit eggs to hatch outside the mother's body. Reproduction in bony fishes varies; most lay eggs that hatch later, but some give birth to live offspring. Coelacanths give birth to live offspring.
Walker, Sally M.
Fossil Fish Found Alive: Discovering
Minneapolis: Carolrhoda Books, 2002.
Traces the scientific detective work that led to identification of this species, and describes
findings about its physiology, habits, and habitat.
A Fish Caught in Time: The Search
for the Coelacanth.
New York: HarperCollins, 2000.
Provides firsthand accounts from coelacanth researchers, including Marjorie Courtenay-Latimer.
Jewett, Susan L.
"On the Trail of the Coelacanth, a Living Fossil."
The Washington Post, November 11, 1998,
page H1. Online at: www.washingtonpost.com/wp-srv/national/horizon/nov98/fishstory.htm
Tells the story of the accidental spotting of a coelacanth by a biologist vacationing in Sulawesi, Indonesia, and his subsequent efforts to acquire
a specimen for scientific study.
NOVA's Web Site—Ancient Creature of the Deep
In this companion Web site for the NOVA program Ancient Creature of the Deep, examine the anatomy of a coelacanth, take a true-false quiz on the coelacanth, read the letters sent between the woman who discovered the coelacanth and the scientist who named it, and take a look at other fossil fish.
Coelacanth: The Fish Out of Time
Includes sections on biology and behavior,
conservation, recent news, and video clips.
Find a Fish: Coelacanth
Relates the discovery of the first living coelacanth off the Comoros Islands, the subsequent discovery of the species near Indonesia, and the ways in which coelacanths differ from other living fishes.
The "Fish Anatomy" activity aligns with the following National Science Education Standards.
Science Standard C:
Structure and function in living systems
Living systems at all levels of organization
demonstrate the complementary nature of
structure and function. Important levels of
organization for structure and function include cells, organs, tissues, organ systems, whole organisms, and ecosystems.
Diversity and adaptations of organisms
Millions of species of animals, plants, and microorganisms are alive today. Although different species might look dissimilar, the unity among organisms becomes apparent from an analysis of internal structures, the similarity of their chemical processes, and the evidence of common ancestry.