While most sea stars have five arms they use for grasping prey and holding on to rock, the sunflower star (Pycnopodia helianthoides) is a large exception with up to 24 arms, and an overall larger body size compared to most other species on the coast of North America.
As can be seen in this post's photo, the common name is derived not only from its large, disc-like appearance, they can achieve a maximum diameter of 36 inches (91 cm); but also because of the myriad protuberances covering its upper surface like the seeds in a sunflower. These include external gills, tube feet and small pincer-like appendages called pedicellaria that help keep the upper surface clean.
Besides being among the largest sea stars in the world, the sunflower star is also notable for its fast cruising speed and extra flexible body compared to other sea stars. Able to sprint at about 39 inches per minute (1 m per minute), the sunflower star can track down mobile prey that other sea stars would be unable to catch. And while most sea stars have a rather rigid body structure made of interlocking pieces, the sunflower star's internal structure is only loosely connected, allowing it to easily move over the reef, squeeze into spaces other stars can't, and even expand its mouth wide enough to swallow whole sea urchins, which it digests internally, spitting out the un-digestible hard parts. Because of this ability, aggregations of sunflower stars can often be found lurking around the edges of urchin barren areas snacking on easy prey.
When it comes to reproduction, sunflower stars can reproduce by either asexual fragmentation, or sexual broadcast spawning. By casting off an arm or two that can crawl away and grow into a new individual with an identical set of genes, sunflower stars can reproduce by themselves. With separate sexes, sunflower stars also breed by releasing sperm and eggs into the water where fertilization occurs. To spawn, individual sunflower stars will push themselves up off the bottom on a number of arms and release their gametes (eggs or sperm) into the water. After fertilization, the egg divides to form a larva that will drift on ocean currents for 2 to 10 weeks before settling to the bottom.
This photo was taken with a Canon EF100 mm f/2.8 macro lens on a Canon EOS 10D in an Ikelite underwater housing. Lighting was provided by two Ikelite DS-125 Substrobes in eTTL mode. The exposure was set to 1/60 sec at f/22 and ISO 800.
Visit www.chuckkopczakphotography.com to read more blogs or see more of my photos.