Can you please clear something up to me on the matter of sea cucumbers?
My invertebrates professor told us that, like starfish and sea urchin, the cucumber is spherically symmetrical, because it was like taking a sea urchin and elongate it. But it doesn't seem reasonable to me because they have a dorsal side and a ventral side, or they wouldn't be able to move on the sea bed, no? Surely, they're of bilateral symmetry.
I'd be very grateful if you'll riddle me this, it's been bugging me since my first year's first semester...
Sea cucumbers are in fact much like urchins that are elongated along the oral-aboral axis. Remember that urchins and sea stars have a dorsal and ventral side too. The ventral side is where their tube feet and mouthparts are. Sea cucumbers also have tube feet and mouthparts on their ventral side, but their tube feets are modified for feeding and are located around the mouth.
The Echinoderms are radially symmetrical, not spherical, meaning that a radius is drawn out from a central point of origin. Sea cucumbers are 5-rayed, like urchins and most sea stars. You can see this best in cross-section. These 5 rays are really longitudinal lines, called ambulacria, also with tube feet. These 5 ambulacria, 5 rows of tube feet, and the presence of ossicles in their in their leathery skin (reduced to small spicules which make them more felxible) are the other reminder of their sea star ancestry.
I hope this helps, feel free to ask anything else about marine invertebrates.
Kevin works at the Duke Marine Lab as a researcher at the Marine Conservation Molecular Facility studying the population genetics of vent fauna. He has an M.Sc. in Biology from Penn State where his research focused on marine invertebrate systematics and the community structure of chemoautotrophic foundation fauna at hydrothermal vents. Visit Kevin's personal website, where his CV lives, and follow him on Twitter, Flickr, Friendfeed, YouTube, Nature Network, Amazon, Research Blogging and Facebook.
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Eric worked in Satellite communications, computers and design for many years, but returned to school to pursue his early love of marine sciences. He is curently working on his Masters in Biological Oceanography at the University of Connecticut's Avery Point Campus. Eric also photo-blogs at Larval Images, has a personal site at Eclectic Echoes and his images are available on Flickr.
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ReplyDeleteCan you please clear something up to me on the matter of sea cucumbers?
ReplyDeleteMy invertebrates professor told us that, like starfish and sea urchin, the cucumber is spherically symmetrical, because it was like taking a sea urchin and elongate it.
But it doesn't seem reasonable to me because they have a dorsal side and a ventral side, or they wouldn't be able to move on the sea bed, no? Surely, they're of bilateral symmetry.
I'd be very grateful if you'll riddle me this, it's been bugging me since my first year's first semester...
Good question meirav,
ReplyDeleteSea cucumbers are in fact much like urchins that are elongated along the oral-aboral axis. Remember that urchins and sea stars have a dorsal and ventral side too. The ventral side is where their tube feet and mouthparts are. Sea cucumbers also have tube feet and mouthparts on their ventral side, but their tube feets are modified for feeding and are located around the mouth.
The Echinoderms are radially symmetrical, not spherical, meaning that a radius is drawn out from a central point of origin. Sea cucumbers are 5-rayed, like urchins and most sea stars. You can see this best in cross-section. These 5 rays are really longitudinal lines, called ambulacria, also with tube feet. These 5 ambulacria, 5 rows of tube feet, and the presence of ossicles in their in their leathery skin (reduced to small spicules which make them more felxible) are the other reminder of their sea star ancestry.
I hope this helps, feel free to ask anything else about marine invertebrates.