What are crinoids? Carboniferous life of Texas. Part 2.

Let’s take a look at the general body structure of a crinoid. It consists of a crown, which is essentially a cup with brunched feather-like arms and a long stem attached to the ocean bottom. It resembles a flower and this is why the common name of this animal is sea lily.
Here we have a cup, arms and distal part of arms with tiny branches with pinnules. The specimen were flattened, as often happens with fossils covered with multiple layers of sediments.
Let’s see how different can be the stems of sea lilies. They consist of tiny discs or columnals) with a hole in the center - kind of like donuts or beads. In facts, the discs of fossilized crinoids are often called “Indian beads”.
The discs often have scars in places were small brunches or cirries (one sirrus) were attached. The hole inside of the stem is called lumen. The columnals with cirries are called nodals, others are internodals.
This is a curious specimen, a crinoid stem with another organism, a solitary coral, attached to it. Many crinoids stems are round but there are plenty of those that have a profile in the form of a star or a pentagon.
Now, we will take a closer look at bases of the cup from various species. In the place where the stem is connected to a cup the plates of the cup stick to each other more firmly and can be found together in one piece.
The form of the cup is one of the most distinct features that help scientists to identify the species.
The plates of the cup can also be in single pieces but now you can easily figure out where they are coming from. They are like pieces of a Nature’s jig-saw puzzle or LEGO.
This teeny-tiny plate with pentagonal symmetry was probably attached to the crinoid’s cup serving as a protective scale. But that’s just a guess…
The plates of an upper portion of the cup could have additional parts that were sticking out like thorns providing protection against predators. This is how they looked like. It is said that each spine is a single calcite crystal growing slowly but continuously during lifetime of the animal.
This is a piece of a crinoid arm that was used to collects floating food particles and to direct them toward the cup along the special groove, which is called food groove.
This particular specimen has fragments of side braches or pinnules still attached.
Thank you very much for watching! Please like us if you think this video is interesting and continue to watch other specimens from our 300-million years old collection of Carboniferous fossils. We have specimens of wood, gastropods, brachiopods, nautiloids, clams, sponges, sea urchins, and corals.
All are shown in great details!
Good luck on your trips to search for fossils and other treasures!
Link to the first part:
   • 300-million-year-old fossils like you...  
and to video about microfossils from same localities:
   • Hunting fossils at home - cool microf...  

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