Brittle Star

Associated Smithsonian Expert: Kathy Hollis, M.S.

Kathy Hollis with Triceratops obtusus, collected in 1890 by John Bell Hatcher

Courtesy of Adrienne Block

Kathy Hollis is the collections manager in the Smithsonian National Museum of Natural History Department of Paleobiology. As a kid she would give rocks as gifts, assuming everyone thought rocks were as cool as she did. She majored in geology at the College of Wooster in Ohio and went on to finish a master’s in geology at the Ohio State University in 2005. It was at Ohio State that Kathy realized her love for museum collections. She finished a master’s in Museum Studies at the University of Colorado at Boulder in 2008 specializing in collections care and museum-based research. Kathy has been at the Smithsonian since 2010 and helps to care for one of the largest fossil collections in the world. Her work involves getting the information about what organisms lived when and where out of the collection drawers and making it digital, accessible, and searchable online. Kathy brakes for fossil echinoderms.

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This image was obtained from the Smithsonian Institution. The image or its contents may be protected by international copyright laws.
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Fossil Jurassic brittle star (Ophioderma gaveyi)
Photo by Smithsonian Institution, Department of Paleobiology

About Brittle Stars (Class Ophiuroidea): Paleobiology

Brittle stars first show up in the fossil record in the early Ordovician (almost 500 million years ago). The earliest brittle stars had five arms arranged around a central body (pentaradial symmetry), like modern brittle star. Some species looked like they had zippers on their arms because of the two parallel rows of skeletal parts on each arm (modern brittle stars have just one). Brittle star fossils are rare because their skeletons are delicate (brittle) and tend to fall apart. A common brittle star fossil is Ophiopetra lithographica, perhaps because its unusually heavy, spiny arms and stout jaws fossilize well. It may have been a carnivore, eating small organisms on the sea floor. Brittle stars were nearly wiped out in the mass extinction event at the end of the Paleozoic (about 250 million years ago) but became widespread and diverse again during the Cenozoic. Today, there are more than 2,000 species.

Body plans of types of fossil echinoderms
Photo by Mary Parrish, Department of Paleobiology, Smithsonian Institution

About Echinoderms (Phylum Echinodermata): Body Plan

Echinoderms stand out as the only organisms on Earth with five arms or other elements spaced evenly around a central point. This pentaradial symmetry (penta = “five;” radial = “around a central point") is obvious in some echinoderms, such as sea stars or brittle stars that have five arms. It’s more subtle on others, such as the five rows of tube feet on a sea cucumber or five grooves on a sand dollar. This unusual symmetry of adult echinoderms is not found in juveniles. In fact, echinoderm larvae have two-sided (bilateral) symmetry like humans, and must undergo a metamorphosis to become pentaradial adults. Body plans of animals during their development often say something about their ancestry. The bilateral bodies of developing echinoderms are a reminder that, aside from other back-boned animals (vertebrates), echinoderms may be our closest relatives. Unlike most living echinoderms, many fossil echinoderms did not have pentaradial symmetry.