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Types of Echinoderms

Describes the four main classes of echinoderms.

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Here Piggy Piggy
Teacher Contributed

Pigs In The Deep

The Mighty Sea Pig (Scotoplanes sp.). Can you tell the front end from the back?


Deep-sea Holothurians

Student Exploration

Little Pig, Little Pig...What Are You doing?

Some of you may have encountered the echinoderms known commonly as sea cucumbers (Holothurians scientifically). This encounter may have occurred in a restaurant or aquarium or along the sea shore, but it probably didn't occur in the deep-sea. Still, sea cucumbers are well known members of deep-sea communities, and by well known I mean we know they are there, but not what exactly they are doing there. The deep-sea contains magnificent ecosystems, but they are difficult and expensive to study and much work remains to be done. One thing that has become apparent is animals acquired some amazing forms to deal with the challenges they face. Take a look at this sea cucumber (Scotoplanes globosa) that lives in the deep-sea and doesn't look like your average sea cucumber.


One thing that is striking about this organism is its "legs" or podia. This sea cucumber doesn't crawl or stay put like some of its cousins, that much is clear, but what survival advantage do these podia convey? It could be as simple as podia are a faster mode of locomotion and allow them to find more food in an area of variable resources. But they sure don't seem to move fast. It could be they are avoiding stirring up the sediments and disturbing the "scent trail" they may use to find food, but for now we really don't know.

One of the characteristics of Scotoplanes scientists do know is they can occur in large groups and their population abundance seems highly variable. In this video, you can see a modest-sized grouping moving across the sea floor. Notice how they are all oriented in the same direction. This phenomena may be related to how they find food. Scientists think they may use smell (as mentioned above) to determine the location of "fresh" food and these groups form from the organisms following a scent.


Extension Investigation

Use the resources below to answer the following questions:

  1. How much can the abundance of Scotoplanes vary annually? How do scientists think this phenomena may be linked to occurrences at the ocean surface? Design an experiment (luckily you have unlimited funding) to determine what is the cause of these fluctuations.
  2. What appears to be the relationship between size and abundance for species in the deep-sea? Can you think of a reason that would explain this relationship?
  3. What kinds of fertilization and development (i.e. internal vs. external fertilization, asexual vs sexual reproduction, parental care vs.no parental care) do we see in sea cucumbers as a group? Do these relationships surprise you? Why or why not?
  4. Where does most of the deep-sea get its "food" from? How does this food supply vary in time and space? What does this mean for organisms that live in the deep-sea?
  5. What have scientists learned about biodiversity in the deep-sea? Why was this result unexpected?
  6. Notice in the videos that feeding sea pigs will move two "tentacles" to their mouth at a time and seem to always pair the same two tentacles. Can you think of a reason why this might be the case? Can you design an experiment to test your hypothesis?

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