The white projections from the arm stalks in this closeup view are called pinnules. This crinoid has its arms retracted. Though many may feed during daylight hours, crinoids normally are nocturnal, and commonly keep the arms in a retracted position during the day. The tiny cilia lining the pinnules are also retracted and not visible in this photo.
To cite this page:
Myers, P., R. Espinosa, C. S. Parr, T. Jones, G. S. Hammond, and T. A. Dewey. 2018. The Animal Diversity Web (online). Accessed at https://animaldiversity.org.
The Animal Diversity Web is an educational resource written largely by and for college students. ADW doesn't cover all species in the world, nor does it include all the latest scientific information about organisms we describe. Though we edit our accounts for accuracy, we cannot guarantee all information in those accounts. While ADW staff and contributors provide references to books and websites that we believe are reputable, we cannot necessarily endorse the contents of references beyond our control.
This material is based upon work supported by the
National Science Foundation
Grants DRL 0089283, DRL 0628151, DUE 0633095, DRL 0918590, and DUE 1122742. Additional support has come from the Marisla Foundation, UM College of Literature, Science, and the Arts, Museum of Zoology, and Information and Technology Services.
The ADW Team gratefully acknowledges their support.