Thursday, August 2, 2012

Tide Pool Touch Tank - Echinoderms

I've had a few opportunities lately to work in the visitor center at Hatfield Marine Science Center where I'm interning and it's a lot of fun!  But I feel that I don't know as much as I should about all the animals.  People like to hear interesting things about each of the creatures.  The VC has a book with one page about each animal.  Most, but not all, include some interesting "fun facts" which are the things people want to hear.  So I hope to do a bit of research and find more fun facts about each.  I'll try to site sources for things.  If it says HMSC for the source, it's from the fact sheets in the volunteer binder.

Phylum Echinodermata (Echinoderms)
Class Asteroidea
First, a word on sea stars in general.  I found this site (A Snail's Odyssey), which is amazing!  I have sited it frequently here, and will probably continue to use it, so please check it out if you want to learn about shallow-water benthic/ marine invertebrates (aka mainly tide pool creatures) of the west coast of North America.

Spiny pink star (Pisaster brevispinus)
  • Has a raised, hump-like central disk (
  • Lives below the low tide mark, which is why they are unfamiliar to tide poolers (HMSC)
  • Largest 5-armed sea star in the world (Snail's Odyssey)
  • Has pedicellariae (see explanation below)- little clusters of pincers to ward off predators (Snail's Odyssey)
  • When a sunflower star predator comes along, most sea stars will run away, but the spiny pink star will stand its ground, relying on its pedicellariae to defend itself (Snail's Odyssey)

Side bar (even though it's not on the side): An explanation of pedicellariae (cause I had no idea what they are).  This is taken from a most excellent explanation on Snail's Odyssey, which I will summarize here.  To save me from having to link every single thing: *All pictures, videos, and summarized info is from Snail's Odyssey.

Pedicellariae are small pincer-like jaws used for defense and found on skin surfaces of sea stars, mostly from the order Forcipulatida.  Members of this order found at the HMSC touch tank and explained here in this post are the Spiny pink star, Rainbow star, Ochre star, and False ochre star.
Purple clusters of open pedicellariae
Watch a video of a pedicellaria biting the end of a pin
Pedicellariae of the Velcro Star

One species, the aptly named Velcro star (Stylasterias forreri), has a sophisticated system of pedicellariae which is quite fascinating.  The clusters of pedicellariae around a spine are drawn up when stimulated and this species actually uses this system in the acquisition of small fish to eat!


As you can see, these are pretty serious little structures.  Below, you can see a diagram of the muscles involved in the action of these jaws. 

Watch an animation of a pedicellaria cluster elevating and opening (Snail's Odyssey)


Rainbow star (Orthasterias koehleri)

Rainbow star in normal state (Snail's Odyssey)
Rainbow star with spines erected in response to an
unknown disturbance.  The pedicellariae are also extended
in tufts around each spine, which accentuates the spiny
appearance of this individual

Leather star (Dermasterius imbricata)
Leather star at HMSC
  • Have a garlic or sulfurous odor
  • Soft corduroy appearance is from their skin gills
  • Usually swallows prey whole and digests internally
Bat star (Patiria miniata)
Bat star at HMSC

Ochre star (Pisaster ochraceus)
  • Has pedicellariae (explained above)
  • Orange and purple varieties
  • Can last longest of any sea star out of water - up to 50 hours in shade or under moist algae
False ochre star (Evasterias troschelii)

Dwarf brittle star (Amphipolis squamata)

Daisy brittle star (Ophiopholis aculeata)

California sea cucumber (Parastichopus californicus)

Purple sea urchin (Strongylocentrotus purpuratus)

red sea urchin (Strongylocentrotus franciscanus)

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