Shocking Revelation about Starfish Anatomy: Just a Head

Two starfish on the beach
Recent research reveals that starfish anatomy is even stranger than previously thought

Most animals in the world are what biologists refer to as “bilateral”—their left and right sides mirror one another. It is also typically easy to tell which part of most animals is the top and which is the bottom. The anatomical arrangements of certain other animals, however, are slightly more confounding, for instance in the case of echinoderms, which include sea urchins, sand dollars and starfish. These animals are “pentaradial”, with five identical sections of the body radiating from a central axis. The question of how these creatures evolved into such a state has been a puzzle pondered by many a biologist, with little progress made until recently. In a new study published in Nature, scientists closely examining the genetic composition of starfish point to some key evidence that suggests a starfish is mostly just a head.

Starfish are a deuterostome, belonging to the superphylum Deuterostomia. Most deuterostomes are bilateral, leading scientists to believe that, despite their peculiar body plan, starfish evolved from a bilateral ancestor. This is supported by the fact that starfish larvae actually start out bilateral, and eventually transform into the characteristic star shape. But where the head of the starfish is, or whether it even has one, has proved difficult for scientists to parse out, especially since their outward structure offers no real clues.

There have been a number of theories posited, such as the duplication hypothesis—where each of the five sections of a starfish could be considered “bilateral”, placing the head at the center—and the stacking hypothesis, which asserts that the body is stacked atop the head. In a bilateral body plan, anterior genes broadly code for the front, or the head-region, and posterior genes code for the trunk, or the “torso”, and tail. Researchers in this new study looked at the expression of these genes throughout the body plan as a possible source of clarity as to which part of the starfish is its head and which parts comprise the body.

To this end, researchers used advanced molecular and genetic sequencing techniques including RNA tomography and in situ hybridization. RNA tomography allowed them to create a three-dimensional map of gene expression throughout the limbs of the sea star Patiria miniate. In situ hybridization is a fluorescent staining technique that offered them a means by which to examine where exactly anterior or posterior genes are expressed in the sea star’s tissue, providing a clearer picture of genetic body patterning.

Remarkably, scientists found that anterior or head-coding genes were expressed in the starfish’s skin, including head-like regions appearing in the center, or midline, of each arm, while tail-coding genes were only seen at the outer edges of the arms. Perhaps even more remarkable was the lack of genetic patterning accounting for a trunk or torso, leading scientists to the conclusion that starfish are, for the most part, just heads.

Whether this holds true for other echinoderms remains to be proven, and further investigations into starfish anatomy may seek to pinpoint where in the timeline the trunk was lost. Overall, research like this helps scientists understand how life came to look the way it does. Oddly shaped creatures like the humble starfish can offer insight into the strange evolutionary processes that result in such rich biodiversity across the animal kingdom.


Works cited:

  1. ‘A disembodied head walking about the sea floor on its lips’: Scientists finally work out what a starfish is | Live Science
  2. Molecular evidence of anteroposterior patterning in adult echinoderms | Nature
  3. Starfish Are Heads–Just Heads – Scientific American
  4. Study reveals location of starfish’s head | Stanford News

Uncovering the Origins of the Commensal House Mouse

Figure of house mouse. Copyright George Shuklin.
📷: George Shuklin

When I encounter my cat fixated on specific locations in my kitchen, her behavior shows me that she has heard some mice in those areas. In fact, mice have been attributed as a reason that cats became companions to humans. Mice start gathering and reproducing so cats followed the food source and hunted the rodents, thus endearing themselves to humans, who were storing food for their own use. However, new evidence described in Scientific Reports has shown that mice have been associated with humans even before grain storage was widespread. In fact, by making our dwellings comfortable, we also created an inviting place for mice to live.

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Which Came First: The Virus or the Host?

They existed 3.5 billion years before humans evolved on Earth. They’re neither dead nor alive. Their genetic material is embedded in our own DNA, constituting close to 10% of the human genome. They can attack most forms of life on our planet, from bacteria to plants to animals. And yet, if it wasn’t for them, humans might never have existed.

3D structure of a coronavirus, viral evolution
A depiction of the shape of coronavirus as well as the cross-sectional view. The image shows the major elements including glycoproteins, viral envelope and helical RNA. This file is licensed under the Creative Commons Attribution-Share Alike 4.0 International license.

No, that’s not the blurb for a new Hollywood blockbuster, although recent developments have proven, once again, that truth is decidedly more bizarre than fiction. Now that “coronavirus” has become a household word, the level of interest in all things virus-related is growing at an unprecedented rate. At the time of writing, coronavirus and COVID-19 topics dominated search traffic on Google, as well as trends on social media. A recent FAQ on this blog addresses many of the questions we hear on these topics.

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Science Visitors Only: Watching Life Grow on a New Island

We spend a lot of time looking at history and imagining—”what was it like when…?” As a biologist, I find myself most drawn to stories about the evolution of life. Why does this plant have purplish leaves? How did this species end up in a symbiotic relationship with this other species? How did this animal get to this tiny island 20 miles off the Southern coast of Iceland?

The volcanic island of Surtsey erupting in 1963.
The newly formed island of Surtsey erupting in 1963.

That last one was too specific to be rhetorical, wasn’t it? The volcanic island of Surtsey broke the ocean surface on November 14, 1963, and continued to erupt until June 5, 1967, reaching its maximum size of 2.7 km2 (about the size of Central Park in New York City). At this size, it was large enough to be a good site for biocolonization. Only a few scientists are allowed to visit the island, ensuring that colonization of the island can occur without human interference. Continue reading “Science Visitors Only: Watching Life Grow on a New Island”

Common Misconceptions About Scientific Terms

science-lecture-DNAScience touches our lives every day, yet far too often, scientific concepts become misrepresented in the media. This problem is not an innocent one; swaying public opinion on policies about climate change and vaccination has a large impact on public health. It is the responsibility of every person to achieve a basic level of scientific literacy. More important than being able to recall a library of scientific facts is the decision making process we go through; a mindset that is asking questions and addressing uncertainty can serve as a barrier against deception. Understanding the words common among scientific studies should help non scientists navigate through the sea of information they encounter online.

This article covers nine common misconceptions about scientific terms. We recognize that there are hundreds of words that are misused, so we encourage your contributions below.

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