Living Fossils: Crinoids

Stalked Crinoid/Sea Lily/Flower Impersonator Extraordinaire

Stalked Crinoid/Sea Lily/Flower Impersonator Extraordinaire

This past week, two crinoid scientists, Charles Messing and Tomasz Baumiller, were visiting the island to continue research on the crinoid populations here in Roatán. Primarily, they were interested in the regeneration of crinoid arms after predation. A few individuals in the Lophelia Reef area have given them a sense of the relatively slow regeneration process of these creatures. If a crinoid was a land-based creature, no doubt we would already have tomes dedicated to their life histories, physiology, and genome. But, as with many deep sea creatures, there’s a lot we don’t know about crinoids. So let’s at least visit what we do know…

Crinoids are animals, not plants. Yeah, I know. These floral impostors had me tricked, too. Crinoids are echinoderms – think starfish, sand dollars, and sea urchins. All echinoderms are pentamerous, which means they are radially symmetric with five arms. In the case of crinoids, the arms are organized in patterns of five: some individuals may have more than five arms, but the number will always be a multiple of five. And yes, crinoids are damn good piano players (just take a look at the video we shot).

So in that pentamerous sea of arms, where the heck is the mouth? And how do they possibly eat with those pine needle protrusions? Good questions. Let’s take a look at crinoid anatomy for a quick sec:

crinoid anatomy

Modified from Bather, F.A. 1900. The Echinodermata. pp. 344p. IN: Lankester, E.R. (eds.) A Treatise on Zoology, Part III. Adam and Charles Black, London. © 1998 William I. Ausich

If you were to strip off the pinnules of the crinoid’s crown, you’d essentially have a mutant chicken claw. And that, my friends, is exactly what fossilized crinoids look like. If you ever find yourself in the midst of a fossil expedition, trudging through the foothills of Montana and you see something like this:

Crinoid Fossil

Crinoid Fossil. Image from http://www.fossilmuseum.net

You can impress your fellow fossil foragers: “Just your friendly Paleozoic suspension feeder, ya’ll!” But seriously, here’s how crinoids eat: the pinnules are pivotal for capturing food; each is comprised of many tube feet (you can see them juuuust barely in the photo below) that enable the crinoid to flick food into this feeding groove, which facilitates the transport of delicious blobs of mucous-covered morsels (diatoms, invertebrate larvae, etc.) to the mouth.

Tiny little tube feet protruding from the pinnules.

Tiny tube feet protruding from the pinnules. Image from http://www.nova.edu

After setting up shop on a rock, they just sway to and fro with currents and upwellings, allowing the water to push bits of morsels into their pinnules. This type of feeding behavior relegates crinoids to possibly the laziest group of animals ever: the couch potatoes of the sea!

Crinoids can crawl, fly, and boogie. There are two main types of crinoids: sea lilies, which refer to the stalked (aka stationary) variety and feather stars, which refer to the sessile (aka mobile) variety. Take a look at this Monterey Bay Research Aquarium video for an awesome shot of a dancing feather star.

Here in the deep waters off of Roatán, we see primarily sea lilies, although feather stars make an appearance every so often. The primary physical difference is the absence of a stalk in the mobile feather stars. Instead, they have cirri, which are used to grip on to hard substrate or act as feet to crawl along surfaces. Scientists speculate that the motile feather star evolved from the stalked variety some 250 million years ago in response to predation by sea urchins (Baumiller et al. 2010).

Feather start gripping a rock with its cirri. Photo by BN Sullivan (http://scienceblogs.com/photosynthesis/2009/08/12/getting-to-know-crinoids-throu/)

Feather start gripping a rock with its cirri. Photo by BN Sullivan (http://scienceblogs.com/photosynthesis/2009/08/12/getting-to-know-crinoids-throu/)

 

Crinoids are one of the oldest living fossils on Earth. Quite a few marine species hold this title, including the frilled shark, nautilus, sponge, coelacanth, and horsehoe crab. Crinoids, for some reason, don’t even make it into the honorable mention category for “oldest species on Earth” Google search websites. In fact, for quite some time people thought they had gone extinct because our access to the deep sea was so limited for so long. And it’s not like a deep sea crinoid is ever going to wash up on shore. But the 150 million year-old Frilled Shark ain’t got nothing on Crinoid’s 400 million year track record! Here’s a sweet pic of a fossilized croinoid:

Crinoid Fossil

Crinoid Fossil

We are planning to start a marathon of dives within the next two weeks, so check back soon for some fresh footage!

——-

Sources:

http://www.paleosoc.org/Crinoids.pdf

http://tolweb.org/Crinoidea

Baumiller et al. 2010 Post-Paleozoic crinoid radiation in response to benthic predation preceded the Mesozoic marine revolution. Proc Natl Acad Sci 107:13

doi: 10.1073/pnas.0914199107

 

 

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~ by twonakedapes on May 13, 2014.

One Response to “Living Fossils: Crinoids”

  1. […] Changing Seas. This episode features the visiting crinoid scientists mentioned in the Living Fossils: Crinoids post from […]

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