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Split starfish grows another body, voices squeak, 2004 leaps

Q: How can starfish be split in two and still live? — Rob, Winnipeg, Manitoba, Canada

Sunflower starfish of the northeast Pacific can reach 5 feet (1.5 m) [Ronald L. Shimek, Reefkeeping.com]

A: Many don’t live. Most badly damaged starfish get infected and die or some predator eats them, says Ron Shimek, invertebrate zoologist.

A starfish, however, can — not merely live after being split in two — but repair itself and grow another starfish. Some starfish species (the species group, Linckia) can regenerate when chopped into tiny 1/2-inch (1 cm) pieces. Each piece can develop into a whole starfish.

To grow a new body, though, most starfish need a whole arm and at least one-fifth of their central disk. The torn part sprouts a tiny starfish from the cut arm and grows this miniature star into a complete adult in a year. (Related figure: starfish sprouting a new tiny one)If the hunk is smaller than an arm plus disk part, the severed piece simply dies and the rest of the starfish regrows the missing arm only.

Starfish may grow new arms or bodies much the way we form fetuses — by splitting unspecialized cells, called stem cells. There are no clear studies yet on how starfish actually regenerate, says Kiyokazu Agata of Evolutionary Regeneration Group, Kobe, Japan.

Stem cells can progressively develop into any kind of specialized cell, like a brain cell. We largely lose this ability upon birth but not entirely. We can still, for example, grow new blood cells from stem cells.

Researchers have figured out how the half-inch (1 cm) transparent flatworm (freshwater planarians) regrows itself. The starfish probably regenerates in a similar fashion. Here’s how the worms do it:

I chop a flatworm in two. Skin cells lying nearby the cut quickly cover the wound and determine where the cells lie in the body. Stem cells gather together under the new skin. Skin cells instruct stem cells to divide and tell them what kind of specialized cells to build. The stem-cell pool develops all the cell types needed to make the missing parts. Soon there are two worms.

By the way, starfish (sea stars) aren’t fish. They’re echinoderms — brainless creatures with a spiny skin covering an armor of tiny bone-like plates. Lacking a head, starfish sense light with eyespots at the end of each arm.

Further Surfing:

Cells Alive: Animation showing how a cell divides

Earth Rochester: Asteroidea (true starfish) by William Chaisson

Aquarium.Net: Sea stars by Ron Shimek

Voices squeak

Q: Why does helium change people’s voices after being inhaled? — Jamillah

A: We talk like Donald Duck because sound travels faster through helium and, in effect, shrinks our heads.

Releasing a helium weather balloon at Antarctica [NOAA]

When we speak, the sound speeds from voice box to lips. Since sound travels faster in helium, the sound reaches our lips sooner with helium than air. It’s as if the path were shorter. The faster sound speed raises the resonant frequency of our vocal tracts. We, sort of, become Oz Munchkins with high squeaky voices.

Every pipe, from our vocal tracts to an empty Coke bottle, has a resonant frequency. Blow air across a bottle. The deep sound we hear is the bottle’s natural frequency in air. Fill the bottle with helium and blow across the top. Now, sound travels faster and the tone sounds higher. The resonant frequency of a tube depends on the length of the tube and the speed of sound through it. The faster the sound speed, the higher the frequency.

Be careful, though. Never breathe helium from a balloon. You need oxygen to survive — and helium contains no oxygen.

2004 leaps

Q: What is the next leap year? — Samuel, Riverdale, Maryland

A: Since you asked the question in 2003, the answer is 2004. The next after that is 2008.

Leap years are those years exactly divisible by 4. But, century years (for example, 1900, 2000, 2100) are leap years only if the year is exactly divisible by 400. So, 2000 is a leap year but 2100 isn’t.

Further Surfing:

WonderQuest: The first leap year

Royal Observatory Greenwich: Calendar

(Answered Jan. 16, 2004)