Many ophiuroids move by powerful arm strokes that lift their disks and thrust them forward. Some species may even swim short distances in this manner. Other species, particu larly those with very long arms, move with a slithering type of motion that pulls them along the substrate. Because of this motion, they are sometimes referred to as "serpent stars" or "snake stars." Only a few species use their tube feet for moving about. Ophiuroids are good climbers; filter-feeding species may cling to rock outcrops or to such other filter feeders as gorgonians and corals in order to position themselves in stronger currents above the sea floor.

Ophiuroids show a range of responses to light intensity, ranging from rapid escape, feeding at night, or color change to behavior that indicates relative indifference to light. For example, Ophiocoma wendtii is a highly photosensitive species that changes color from dark brown during the day to banded gray and black during the night; it moves rapidly away from shadows by crawling into crevices. It has been shown in this species that the arm plates function as compound eyes, focusing light through nerve bundles on the dorsal arm plates.

The best-known adaptation to partial predation in motile animals is probably autotomy, or the self-amputation of ap

Self Amputation
Brittle star (Ophiothrix sp.) scavenges on Alcyonarian coral at night. (Photo by ©Jeff Rotman/Photo Researchers, Inc. Reproduced by permission.)

pendages. Ophiuroids may lose arms and even disks in some amphiurid species. The brittle star's ability to shed parts of its arms has to do with the mechanical properties of the ligaments between the vertebral ossicles of the arms. Stimulation of the nerves at an arm joint causes this particular tissue—mutable collagenous tissue or MCT—to disintegrate, and the arm breaks off. The lost body parts are subsequently regenerated. Regeneration of missing arms may take a few months in warm tropical water but more than a year in cool temperate water.

Several species of ophiuroids are bioluminescent. It has been shown that the nocturnally active Ophiopsila riisei and Ophiopsila californica deter predators by luminescent flashes from their arms, and that their bioluminescence also functions as an aposematic (warning) signal to discourage crustacean predators.

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

Get My Free Ebook

Post a comment