It was a clear winter’s day and Mum and I were walking the dog along the banks of the river. I was dawdling a few paces behind when I spotted something in the sand just ahead of us. “Stop! Don’t move!” I said. Mum froze and the dog looked around. I hurried forward and pointed at the distinctive shape lying in the wet sand. It was a starfish. Mum and I both bent down to admire it. Neither of us had ever seen a starfish in its natural environment. We wondered to each other if it was alive. Mum prodded carefully at one of its limbs. It was soft, not rigid, so we concluded that it was. We fished out a smartphone and took a few snapshots. The dog waited patiently, admiring the view. Then I wondered whether we should attempt to put the starfish back in the water, in case it dried out and died. We both stood contemplating this idea. Then I realised that the tide was coming in and the starfish would soon be waterborne anyhow. We decided to leave it.
On the way home, I talked about starfish and other weird and wonderful creatures of the water. I think Mum was more perturbed than interested, but it hasn’t dissuaded me from sharing these fascinating factoids with my followers:
- Most species of starfish have five arms, like the one we found at the river. However some starfishes have seven, some between ten and fifteen and others up to fifty. It is also common for individuals of a five-armed species to have one or two extra arms due to growth abnormality.
- Starfish are basically a hydraulic system. Inside their body is a network of fluid-filled tubes which power gas exchange (breathing), food manipulation (eating), locomotion (moving around) and adhesion (sticking to surfaces).
- Starfish do not stick to surfaces with suction cups (like molluscs) but with an adhesive chemical. Essentially an organic glue.
- All starfishes can temporarily eject their stomach from their body in order to digest food. This enables them to eat prey much larger than themselves, including small fish.
- Starfish do not have well-developed sensory organs but they are sensitive to touch, light, temperature, orientation and the state of the water around them.
- Because they lack brains, starfish do not have the ability to plan their actions. If one arm of the starfish senses potential prey, it will temporarily become dominant over the other arms and move the starfish in that direction.
- Some species of (sexually reproducing) starfish brood their eggs by sitting on top of them in a curved posture. This is most common in polar or deep-sea starfishes.
- Some species of starfish can regrow a lost limb. More rarely, some can regrow an entire body from one limb (which can be a form of asexual reproduction). However the regrowth can take months to years and the starfish is initially vulnerable to infection.
- The maximum recorded life-span of any starfish is 34 years.
- Starfish are able to expel foreign objects from their bodies, which makes them very difficult to tag for research purposes. (I assume that some very frustrated marine biologists found this out the hard way.)
So… starfish facts. Engrossing or just gross?