Starfish don’t have brains

Star shaped echinoderms belong to the class Asteroidea, appropriately, perhaps due to their class name, they have also been known as asteroids.? For the un-initiated their biological shape gives rise to their naming convention.?

The?fossil?record is ancient and sparse, as they tend to disintegrate once dead, information that is available dates them to the?around 450 million years ago in the Ordovician period (known for its meteor strikes).? The Ordovician Period dates from the end of the Cambrian Period, some 486.85 million years ago, to the start of the Silurian Period, 443.1 million years ago.

Starfish don’t have brains, well actually they do, but not centralized like the human brain.? The are rather decentralized into each arm, where Starfish house most of their vital organs.? Perhaps the decentralization allows for some redundancy in a complicated physiology.? They can reproduce via sexual reproduction, there is no external genitalia to distinguish the sexes. Starfish are capable of regeneration, this is considered by some, as a form of asexual reproduction.?

Speaking of arms, a starfish can have up to 12-15 arms, the usual is around 5, that radiate from a central disc. Labidiaster annulatus which lives in the Antarctic, has been recorded with over fifty arms, and with this strange anatomy, that means 50 brains. At the tip of each arm there is an eye, capable of discerning light from dark, a starfish has the same number of eyes as it does arms.

Regeneration

Starfish and chameleons have the ability to regrow parts of their body after amputation, the cells of the starfish are able to correctly differentiate as the limb regrows, to become a functional arm.? Fascinating to think how the new cells regenerate and are able to differentiate to form a new limb, with its vital organs, brain and eye.

What is the mechanism at play, what directs the regrowth and what memory are they drawing from to grow a functional arm?? Some species can even regenerate an entire new starfish from a remaining arm and a bit of the central disc, the system working both ways.? As they say it won’t happen overnight but it will happen, usually in about 12 months.

Starfish regrowing arms picture

All of this physiological activity occurs without blood, or a vascular system that we would be familiar with, or that you would expect would be needed to enact all the molecular signalling.

On the top of the disc there is a small opening called a madreporite, visible usually as a lighter coloured patch.? This spot is like an intake value, where seawater is pumped the starfish and down into tube feet, extending the arms.? Tiny muscles are located in the tube feet, which contract to retract the arms.

Starfish enjoy a hearty carnivorous diet of bivalves, small fish, snails and barnacles.? Its mouth is located on the underside of the disc, and perhaps a good thing it only has one!? It catches it prey, holding the prey in place with it arms and then turns its stomach out.? Once the prey is digested the stomach involutes back into its bodily place, taking the digested animal with it.?

The regeneration powers of this class are fascinating, the mechanism eludes science.? And the current debate about cellular memory, aided and abetted by genetic expression, comes into play.? So to interpret the starfish there must be some memory of how to differentiate or some mechanism by which the correct response to trauma, allows the expression of plural-potent cells.? But the question remains: what directs these cells?

Cellular memory is being explored, with a main posit that body memory, is formed from multi-sensory information, is remembered and stored in the body, is it this mechanism that advises the cell lines how to regenerate?[1]

In many respects starfish live in microgravity, and they have become one with their habitat, replacing blood with seawater, adapted their carnivorous ways to creatively ensure nourishment.? And again, great that they have a mouth count of one.? With their skin made from calcium carbonate, their unusual physiology and regenerative abilities, perhaps another look for potential and novel space medicine should be explored?

[1] Flores A I, Liester M B (November 05, 2024) The Role of Cells in Encoding and Storing Information: A Narrative Review of Cellular Memory. Cureus 16(11): e73063. doi:10.7759/cureus.73063