Back to the past, looking for sea urchins and other deep sea life Sea urchin (Araeosoma belli) with poison sacs on the end of its spines. (Lower, left) Zoologist Dave Pawson ready to descend in a submersible for a deep sea dive. (Smithsonian/Dave Pawson)
Back to the past, looking for sea urchins and other deep sea life
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While this animal looks like a pincushion, you would not find it in a sewing kit. This venomous sea urchin, A. belli, lives on the ocean bottom as deep as several thousand meters. Scientists study it, and other deep ocean dwellers, from submersibles or remotely operated vehicles (ROVs) that explore the ocean depths equipped with cameras and collecting gear. 

But, original observations of these deep-water urchins were made before research submersibles or ROVs were in use. How did scientists back then learn about animals that lurked way beyond the reach of scuba gear?

In 1938 a Danish zoologist, Ole Theodor Jensen Mortensen, described the stomach contents of relatives of A. belli that a trawling ship had brought to the surface. While he was not able to observe the animals alive in their deep habitat, the remarkable observation of plant material inside their bodies led him to propose that some sea urchins were vegetarians. These individuals had apparently fed on plants that had broken off from shallow sea grass beds, or floated down rivers, then drifted down to the deep sea.Drawing of USS Albatross research ship showing its two sailing masts and central smokestack.

Decades later, Mortensen’s discovery was confirmed by other scientists, including Smithsonian Zoologist Dave Pawson, who found sea grass in specimens of A. belli. The specimens are from the historic US Fish Commission Steamer Albatross, the first dedicated U.S. ocean research ship, which made expeditions from 1883-1921. Trawling with long nets for months, the Albatross collected millions of specimens, often from great depths. Aboard the Albatross in 1906 was a young Austin Clark, the ship's lead naturalist. Among the animals Austin catalogued were hundreds of species of sea urchins and relatives that greatly expanded the echinoderm collection at the Smithsonian’s “U.S. National Museum.”  

Echinoderms also include sea stars, sea cucumbers, brittle stars, and crinoids. Their diverse body shapes reflect the range of marine habitats they occupy, from shallow reefs to deep ocean bottom. While sea urchins do justice to the name (echino = “spiny”; derm = “skin”), other echinoderms may be soft, smooth, feathery, or bumpy. What they all have in common is a body with five-part symmetry, obvious in a five-armed sea star but hidden under the skin of a sea cucumber. Austin Clark, in his later work at the U.S. National Museum, described nearly 500 new species of echinoderms. 

Today, scientists continue to study echinoderms, probing mysteries about their life histories. Zoologist Dave Pawson, at what is now called the National Museum of Natural History, combines data from museum specimens, research at sea, and observations of live animals to see what echinoderms reveal about life in the deep sea and its connection to shallow-water habitats. Learn more about his discoveries in a "Smithsonian Science How" webcast video. During “A Century of Discovery of Sea Urchins and Relatives,” Dave will take you on a historical research journey. You can also get teaching resources to use with the webcast.

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CRITICAL THINKING QUESTION
Why was it more difficult to study the deep sea when these sea urchins were first discovered?
Write your answers in the comments section below


COMMENTS (1)
  • annec-cel
    10/27/2017 - 12:14 p.m.

    When the sea urchins were first discovered, the technology for deep sea exploration was not available. They could study the bodies of the creatures that were found in trawler nets but not see how they lived in their environments. Once deep sea animals are brought to the surface, their bodies are generally deformed as the change in pressure causes the animals to expand, burst, and die.

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