"Imagine protists that walk on legs like bugs, or paddle with arms.
Q: How do they do it?
The “arms” that swing back and forth are made of bundles of microtubules, which grow from unique subnuclear microtubule organizing centers (MTOCs) that are unlike the more familiar axonemes of cilia. Surprisingly, this protist can move without the “arms” but gets along faster with them.
Bumps are visible along the lateral arms;
Q: Where did they come from?
Q: And must the commentators beg the question of evolution in the phrase “evolutionary eukaryotic diversity” instead of just describing “eukaryotic diversity”?
These two protists possess only distant morphological similarities to other members of their taxa, so imagining a phylogeny between them seems strained. For now, behold and wonder!
This creature is so weird, you have to watch it in motion to believe it.
The cell body is slightly elongated, and from the major axis two long filaments extend twice its body length forward and backward. This is the axis along which it glides with cilia. But now, picture “arms” extending out to the sides that paddle back and forth, one sweeping forward while the opposite arm sweeps backward.
It’s rare to find the word “incredible” in a formal scientific paper’s title, but Eglit et al., writing in the same issue of Current Biology, must have been astonished when they announced this creature as “a protist with incredible cell architecture.”
This creature is so weird, you have to watch it in motion to believe it.
It’s rare to find the word “incredible” in a formal scientific paper’s title, but Eglit et al., writing in the same issue of Current Biology, must have been astonished when they announced this creature as “a protist with incredible cell architecture.”
“Kingdom-level” branches are being added to the tree of eukaryotes at a rate approaching one per year, with no signs of slowing down. Some are completely new discoveries, whereas others are morphologically unusual protists that were previously described but lacked molecular data.
For example, Hemimastigophora are predatory protists with two rows of flagella that were known since the 19th century but proved to represent a new deep-branching eukaryote lineage when phylogenomic analyses were conducted. Meteora sporadica is a protist with a unique morphology; cells glide over substrates along a long axis of anterior and posterior projections while a pair of lateral “arms” swing back and forth, a motility system without any obvious parallels."
The “arms” that swing back and forth are made of bundles of microtubules, which grow from unique subnuclear microtubule organizing centers (MTOCs) that are unlike the more familiar axonemes of cilia. Surprisingly, this protist can move without the “arms” but gets along faster with them.
Bumps are visible along the lateral arms;
Q: what are those?
A: They are called extrusomes. These granules can move up and down along the arms and can be “fired” at bacterial prey. Once it surrounds the target, the extrusome delivers the bacterial burrito to a food vacuole where it is phagocytosed (digested).
Seen from the side, this protist looks like a cockroach or pill bug scooting along the floor, but it is much tinier. Insects have legs made of cells. This protist is a single cell.
Like all other eukaryotes, M. sporadica is equipped with organelles: a nucleus, mitochondria, longitudinal bundles of microtubules, and molecular motors like dyneins to animate the microtubules. Of course, it also contains all the machinery for metabolism, mitosis, DNA storage, transcription, and translation, in addition to motility.
This is no simple animal.
Q: How can it sprout legs and walk?
The paper describes the coordination between the cirri (sing. cirrus) when the protist moves. There are 10 frontoventral cirri and 5 transverse cirri arranged in an asymmetrical pattern, plus 4 caudal cirri at the tail end. “Distinct cirri are involved in generating distinct gaits,” the authors observe. Each cirrus moves with a power stroke and recovery stroke, like a swimmer. The cilia that line our airways move in a similar fashion, but in Euplotes they stroke in large bundles.
The authors identified three stereotypical movements performed by Euplotes with their cirri:
The paper describes the coordination between the cirri (sing. cirrus) when the protist moves. There are 10 frontoventral cirri and 5 transverse cirri arranged in an asymmetrical pattern, plus 4 caudal cirri at the tail end. “Distinct cirri are involved in generating distinct gaits,” the authors observe. Each cirrus moves with a power stroke and recovery stroke, like a swimmer. The cilia that line our airways move in a similar fashion, but in Euplotes they stroke in large bundles.
The authors identified three stereotypical movements performed by Euplotes with their cirri:
---the swim,
---the forward walk,
---and the sidestep reaction (SSR).
The first two strategies allow the protist to move forward.
The SSR allows it to quickly back up and turn.
While swimming, the asymmetrical pattern of cirri makes it rotate in a helical fashion. But while walking on a surface (like the cover slip of a microscope slide), it scoots along like a cockroach. The authors notice the functional purpose of cirri when they describe them as “compound leg-like structures comprising many cilia.”
It’s exciting to ponder that the world is filled with examples of cellular motility beyond the iconic bacterial flagellum — and we probably don’t know even half of what exists.
The fact that many of them show no clear phylogenetic connection with other microbes, and may contain unique morphological structures, poses a severe challenge to Darwinism. The more isolated diversity, the weaker the argument for common ancestry.
The more unique purposeful motion is discovered,
It’s exciting to ponder that the world is filled with examples of cellular motility beyond the iconic bacterial flagellum — and we probably don’t know even half of what exists.
The fact that many of them show no clear phylogenetic connection with other microbes, and may contain unique morphological structures, poses a severe challenge to Darwinism. The more isolated diversity, the weaker the argument for common ancestry.
The more unique purposeful motion is discovered,
the more the evidence that the biosphere has been engineered for action."
EN&V/Coppedge