Phylum Echinodermata Part 1: Form and Function

With the hemichordates covered let's check out the echinoderms. Echinodermata is the other phylum in the clade Ambulacraria, and they are found all around the world. The most familiar organisms in this clade are starfish or sea stars, sea urchins, sea cucumbers, and more. Let's get an introduction to their form and function.

Script by Ryan Helcoski

Check out "Is This Wi-Fi Organic?", my book on disarming pseudoscience!

[thetboys]

Thank you for making this video and helping me with many things over the years!

[TheShinyShrimp]

he knows a lot about the science stuff for sure

[magroves]

I was excited for this one. I don't know nearly enough about them. It was cool to see what their larvae look like.

[DavidBarrera-ez]

Please professor Dave continue these series, you are great!

[NickArcolla]

I looked deep in her eyes and said: "Signorella, phylum echinodermata"... and she melted in my arms...

[alexhopkins]

In high school, we had a kind of backwoods science teacher, but he was excellent at it! He set up the class exactly like Intro Bio in college. We had several pretty in-depth dissections, including a starfish. Like almost every other group, I accidentally severed the stone canal. The teacher walked up sadly, saying "I thought if anyone, you would get it." I was known as a science guy even back then.

[jamiegallier]

Thanks again Dave. I love this series of tutorials so much.❤

[Siphuncularity]

Fascinating stuff. Seeing how radically different their biology is to ours, it's pretty surprising we're so closely related to these bizarre organisms.

Thanks again, Professor Dave, for all the effort you put into researching & producing these wonderful tutorial videos.

[RyanStrine]

I wish you would do one of these daily...its my favorite series so far

[ErmiusJillian]

please more phylum videos and taxonomy, I'll use it in my Science Olympiad review

[fugamantew]

Long live the empiricists like Prof. Dave! Long live the history of them all, for they are giants and we only are stepping on their shoulders to see

[snowcat]

This one goes out to that guy who was whining about you "moving away from your tutorial content" LMAO

[aisharjabaruachowdhury]

Dear sir, please upload videos on feather stars

[powpuckmobile]

2:30 I think you mean to say autotomy, not autonomy?

[markocrni]

God these species were creepy when I saw them in sea, there were so many

[vertabrate]

this is why Patrick star was my favorite sponge bob character.

[glennpearson]

I often wonder what biochemistry exists in these creatures that allows them to regenerate. Whatever it is, I suppose Deadpool figured it out.

[IGLUPhylogeny]

Regarding the classification of living organisms, I hope someone finds the following thoughts interesting. Any disagreement with what I have written below is welcome.

The sentences like "birds are dinosaurs" or "humans are apes" are a consequence of the "language of monophyletic taxa" which is fundamentally unsuited to speaking about evolution.
(This is also explained in the links below:
Two Youtube videos:
- Ronald Jenner: Seeing Evolution Through a Cladistic Blindfold
- Telling linear stories with branching evidence: tales from the history of narrative phylogenetics
Lineage Thinking in Evolutionary Biology: How to Improve the Teaching of Tree Thinking (Springer article).)

On the other hand, the language of paraphyletic taxa is well suited to telling evolutionary stories. So it makes more sense to say "birds evolved from theropod dinosaurs" or "humans evolved from apes". One must realize that the scope of taxonomic categories is artificial and subjective because anagenesis proceeds in enormously tiny steps (never happened that an Australopithecus female gave birth to a Homo daughter; and no one says Homo is Australopithecus despite the fact that an australopithecus is the ancestor of "genus" Homo). The language of monophyletic taxa then can lead to sentences like "whales are fishes" because fishes are paraphyletic, in other words Devonian fishes are ancestors to tetrapods. Maybe if we want to be pedantic we may disagree that humans evolved from monkeys because humans did not evolve directly from Miocene monkeys but via paraphyletic ape "grade". And now imagine if we do not distinguish between the words and categories of "monkey" and "ape" as in some other languages. Another misleading name is Osteichthyes ("bony fishes") - recently it was found that ancestors of cartilaginous fishes (Chondrichthyes, like sharks and stingrays) lost their bony skeleton secondarily so a shark is also bony fish although it doesn't belong to the taxon Osteichthyes. It just shows how languages, systematics and taxonomy can distort perception of evolution. It also leads to somewhat erroneous sentences like "crocodiles are older than birds" - but if we stopped calling Mesozoic "crocodiles" as crocodiles (and many such "crocodiles" were very different, e.g. herbivorous, aquatic with fins, with long legs and upright posture etc.) then crocodiles suddenly become younger than birds.

One can define a taxon as the living and extinct descendants of the last common ancestor ("LCA"), because it is a natural and unambiguous way how to obtain a taxonomic category (a one single sharp unblurred line dividing birds from the rest). Such clade is called a "crown group". For example all living birds have a LCA which lived in Cretaceous. But one must realize that this LCA was not the first bird and this LCA was not special because the stem lineage of living birds (the crown group) sprouted many now extinct lineages of birds which all had every trait of the crown group.

Unfortunately most of living organisms are extinct - but if there were much less extinctions then we would have much less "modern" "phyla" or "classes", and fossils are one of more reasons why taxonomy becomes somehow redundant. The statement "birds are dinosaurs" is obvious and banal just like "cetaceans are mammals" - it’s not wrong of course, it’s just static monophyletic taxonomy (i.e. hierarchy of nested clades). But the statements that "birds evolved from theropod dinosaurs" or "cetaceans evolved from artiodactyls" is much more better because they contain an explanatory evolutionary story about the origin of birds and cetaceans (the stem lineages of derived taxa are places where massive evolution happens and where monophyletic taxa fail). Also paraphyletic theropods and artiodactyls are morphologically both quite uniform and are in stark contrast with derived crown-group birds and cetaceans. What is misleading are statements like "birds/humans didn’t evolve from dinosaurs/apes but they still are dinosaurs/apes". Such statements don’t take into account that both birds and humans are the most derived theropods/apes. Recently it was found that excavates (biflagellated eukaryotic unicells) are paraphyletic to all the other known eukaryotes. Does it also mean that "echinoderms and cacti are excavates"? Yes, according to monophyletic taxonomy (hierarchy of nested clades). Does it mean that cacti evolved from excavates? Yes, although not directly from excavates but via numerous intermediate organisms which we don’t call excavates. What’s the amount of shared traits dividing a derived taxon from its paraphyletic stem taxon? I.e. how different birds would have to be from theropods not to be considered a dinosaur? What if penguins evolve so drastically that the animal no longer looks like a bird? For example the future animal will be so different from penguin as a cactus is different from an aquatic alga. Apparently such descendant of penguins will also be a dinosaur, a chordate, an animal and newly also an excavate. For example myxozoans are animals although they have lost almost all animal traits. No one can change who their ancestors were. Isn’t then taxonomy somewhat redundant in such extreme cases? Clearly cladograms with higlighted informal paraphyletic taxa are superior because they are explanatory and evolutionary. Isn’t then the name Excavata synonymous with Eukaryota? Shouldn’t then the name Eukaryota be reserved for total group? But we may never discover extinct or living stem eukaryotes which are not descended from excavates.

[MaikKellerhals]

A little dry, and i understood about half of the words. I guess i'm not the target audience. But still very interesting!

[Megtzz]

BRO UR THE MOST GOATED TEACHER EVER PLS LIKE AND REPLY TO MY COMMENT I WANNA FELX TO MY FRIENDS❤