Blastoidea

Echinoderms are awesome

Echinoderms (translated to ‘spiny skin’) are still alive today and you can find their skeletons washed up on the beach. These organisms include sea urchins, sea stars, brittle stars, and sea cucumbers. There are several factors that make an echinoderm an echinoderm!

  • Some sort of five-ish-ness – sea stars have arms in sets of five meaning they have pentaradial symmetry
  • They have a water vascular system. This means that they have a hydraulic system that allows water to be moved through tubes in their body.
  • Mesoderm skeleton made of high magnesium calcitic plates with stereom, a sponge-like, very fine porous internal structure. Stereom is a very echinoderm-specific feature, they are the only group known to possess it.
  • They have connective catch tissue, which is a special type of tissue that can change its properties. Meaning it can be stiff and rigid or loose and flexible!
  • Echinoderms lack a head (cephalization) and they can grow to be relatively large for invertebrate animals.
  • Echinoderms do not have a nephridial system – in animals, this system removes metabolic waste from the body. In humans, this system includes your kidneys that help your body filter and remove waste! Since echinoderms do not have this system they cannot regulate their internal system. This restricts their environmental tolerances, such as changes in salinity. Salinity is the salt content of the ocean and echinoderms can only live in saltwater environments, not freshwater! This is termed stenohaline.

Blastoidea

Blastoidea is the proper name for blastoids – a more colloquial way to talk about them. When scientists talk on a daily basis we tend to use the term blastoid because it is easier to say… although Blastoidea sounds a lot more regal.

How long did they live?

Blastoids lived from the Silurian to the Permian, that totals ~192 million years! That is an incredibly long amount of time and they were a pretty successful echinoderm group. Unfortunately, the end Permian mass extinction was too extreme and they perished alongside many other marine organisms.

What did they look like

Example of how you find blastoids in the fossil record. The well sutured body is all that remains!

If you have ever heard of crinoids (another group of echinoderms, still alive today), blastoids look quite similar. Blastoids, unlike modern echinoderms, do not have the ability to move around. This type of lifestyle is called sessile, it simply means immobile. Blastoids have a root-like structure that helps keep them in place so they can live without being thrown about by currents. There is a stem to elevate them into the water column to feed. They have a body which we call a theca (plural = thecae) and arm like structures to aid in feeding. Unfortunately, the arms, roots, and stem are all made up of many little plates that fall apart very quickly after death. This means that all that remains is the well-sutured (stuck together) theca (body).

Many reconstructions have the arm-like structures as sort of flowing over the body like in this figure but that is what these structures look like when they are dead. It’s more likely that the arms would have stuck out straight from the body (perpendicular to the body) to provide some direction to the water flow over the body.

Respiratory structures

Much of Jen’s research centers on understanding the internal respiratory structures of blastoids. Humans, such as yourself, use their lungs to get oxygen into the blood-stream to get energy to perform various daily tasks. Blastoids have hydrospires. Hydrospires are internal structures (endothecal = inside the body) and they are arguably the most complex of all the extinct echinoderms. They are lightly calcified so they do show up inside the specimens that you can collect but they would have been mesh-like to allow for oxygen exchange into the main body cavity.

An example slice through a Pentremites species with the plates and respiratory structures outlined.

These structures have different morphology on the outside or external part of the body. Consider your own lungs – we don’t really see them on the outside but we know the general shape by examining our torso and rib cage shape. Blastoids have this bud-shaped body that often makes it difficult to envision what their hydrospires look like. We are currently working to create 3D models from 2D slices of specimens, with the end goal of being able to visualize the entire structure in 3D and be able to rotate it on the computer!

Having hydrospires has united (brought together) blastoids as a group. Think of hydrospires as a specific feature – similar to humans having two forward-facing eyes. We would be able to tell that your pet fish was not a human but maybe would have more trouble separating your pet dog or cat. We use these similarities to group extinct animals! Many other really ancient echinoderm groups were separated on the basis of having or not having specific respiratory structures. One of Jen’s research focuses is on determining how accurate that idea really is. Do respiratory structures define the group? Or is it something else? Or is it a group of somethings?! There is much work to be done on respiratory structures. Remember that organisms (even you) need oxygen to perform daily functions. It is an important element in generating energy!

Why should anyone actually care about blastoids?

For starters, they are super cute!!!

Stable morphology

Although blastoids are extinct they still have a lot they can tell us about the 200 million years they were alive. In particular, blastoids have very stable body plates – much like the human skeleton is very stable. Underneath your flesh everyone is nearly identical! We can pick out the same pieces on everyone – blastoids are very similar but they take on a variety of strange forms throughout their entire existence. Since they have such a stable body plan we may be able to pinpoint these changes in their anatomy to specific times in Earth history. Did they change to accommodate changing environmental conditions? Did it have to do with nutrient input? What about the changing climate? Sea level dropping or rising? These are all questions we can address once we have a better understanding of the evolutionary relationships within Blastoidea.

Examples of stable plates on blastoids. Notice the wide variation in shape but the colors indicate the same plates on each specimen. Some are hidden either on top of the specimen or tucked underneath!

Crinoids versus blastoids

Crinoids, commonly called sea lilies or feather stars, are still alive today. Superficially blastoids and crinoids look quite similar, more so in the past than they do to modern forms but why is it that the crinoids made it through the end Permian extinction and blastoids didn’t? What made crinoids more successful? Was it random chance? This is another question that I could team up with fellow echinoderm workers to attempt to address. It gets at the larger question of what makes a successful organism and what traits allow these organisms to thrive even in times of extreme crisis.

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