• Categories

  • Most Popular Questions

  • Recently Viewed Questions

  • Recent Answers

    How To Make a Digita… on What does a frequency of 100 H…
    Daigrepont on Can an earthquake cause air tu…
    Benedict on How did God come into exi…
    joshua on How does the human body g…
    Ian on How did God come into exi…
  • Recent Questions

  • Blog Stats

    • 2,215,023 hits
  • Visitors since 11-3-08

    counter create hit
  • Terms and Conditions

  • Warning

    We are doing maintenance on this site, so some posts may disappear for a short time. Sorry. Normal service will soon be resumed...
  • Pages

  • February 2008
    M T W T F S S
        Mar »
     123
    45678910
    11121314151617
    18192021222324
    2526272829  
  • Archives

  • Meta

Why do starfish have 5 legs?

Why do starfish have 5 legs or arms?
George Carsley from Warwickshire (age 5-14)

How is star fish shaped like a star?
Abid Hossain + Jack Huang + Eddy Liou from Swansea (age 5-14)

Advertisements

One Response

  1. Starfish – or sea stars, to underline the fact that they are not related to fishes – belong to the family Asteroidea (from aster, Greek for star) and with other species like the sea urchins, they form a group called the echinoderms, the “spiky skinned”. Most of these animals show a radial symmetry of their adult body shape while other species, like humans or insects, exhibit a bilateral body symmetry (we have “left” and “right”, “back” and “front”, words that would have no meaning for a starfish).

    But when you look at the larvae of echinoderms you realize that these are organized bilaterally as well, so the radial form is a secondary development that only happens in some echinoderms when they become adults (see e.g. http://www.microscopy-uk.org.uk/mag/artjul00/echino4.html and http://www.microscopy-uk.org.uk/mag/art98/janstar.html).

    So, most of the starfish develop from their larval stages to adults with five “arms” but there are also species with more or less than five arms and the reason why some have five and others seven or nine is not known but might depend on different environments or feeding/locomotion strategies.

    On the other side, the reason that the starfish are radically shaped might come from the fact that they don’t move fast, don’t hunt and don’t have to (or can not) run away from predators, so they simply do not need to have a front or back, a left and right, something that gives them a sense of direction.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: