Octopus
questions galore, Space station speeds, Women sizes & the government
Q: How long are an octopus' arms? What is a siphon?
Do octopuses have bones? How did octopuses get so intelligent? Why don't
octopuses have bones? How do octopuses change colors? Erin, Fairview,
Illinois
An octopus and his funnel. Photo courtesy of Roy Caldwell and the University
of California at Berkeley, copyright, used with permission.
A: How long are an octopus' arms? It depends on the octopus. The smallest
pygmy species
— a mere seven tenths of an inch in body length — has about one-inch (2.5 cm) arms. Whereas, the biggest (2-foot
body length) has over100
times longer arms. The common octopus has about five-foot (1.5-m) arms.
An octopus' siphon is a tube (see figure) that lets him jet through the sea, breathe out,
and hide in an inky plume. "The siphon and the funnel are the same thing.
I prefer to use the term funnel because water is not sucked in through the
funnel, it is expelled," emails biologist
Roy Caldwell, professor of integrative
biology at the University of California at Berkeley.
The octopus sucks water into the mantle (body) cavity through a different
tube and passes the water over the gills. His funnel/siphon tube expels the water, jet fashion. He can
squeeze his body hard, thereby, expelling water fast and jetting fast, but usually, he squeezes the water out
gently, and moves primarily by crawling the seafloor. If threatened,
he shoots out a dark plume to mask a jet-away.
The plume is actually red, and made of melanin (the same dye that colors our
hair and skin) but looks dark in the sea's dim lighting and when concentrated.
Also, red light looks gray since water absorbs its long-wavelength light.
Moreover, the ink contains an irritating compound (tyrosinase) that briefly
destroys a predator's sense of smell, enhancing the wily octopus' vanishing act.
The boneless octopus, as symmetrical as a creature can be, needs much brain
processing
to control posture and orient itself spatially. "But that does not equate
to intelligence," says Caldwell. Biologists debate an octopus'
intelligence; the issue isn't decided. I'll explore this topic another
time.
Why boneless? Well, it has
at least one advantage: an octopus can slip through a hole as small as his
eye.
 This
octopus displays a brilliant orange. "Most octopuses will let you get close, maybe even touch them," says diving
submersible Alvin pilot and photographer Bruce Strickrott. In the Gulf of
Mexico, about 7500 feet (2300 m) deep. Photo courtesy of Woods Hole
Oceanographic Institution.
An octopus changes colors by displaying pigments and
sheens. An octopus starts with a couple of basic colors — brownish-red and
yellowish-orange. His color organs are "a bag of colored material
surrounded by muscles," says Caldwell. By stretching the muscles he can
open the bag more and reveal more
colors.
Just as easily, he can cut off the colors by relaxing his muscular color bag,
which then contracts to a "pinpoint of concentrated pigment" that we don't see. Moreover, he can adjust his skin color by changing small bodies (called iridocytes) below the pigment layer. Light
bends and bounces off these cells to cast a blue-green sheen over his skin, like a
peacock's feathers, subtly varying as light hits from different angles.
By the way, several octopus species drop their arms off their body when
attacked. "The wiggling autotomized arms will even lock onto the predator
with its suckers," says Caldwell. "This is usually sufficiently
distracting to allow the octopus to escape." Re-growing lost arms is a
snap for an octopus.
Further Reading:
Why an octopus has three hearts, WonderQuest
What
is octopus ink by Nancy King, Tonmo.com, the octopus news magazine online
International Wildlife encyclopedia,
edited by Maurice Burton and Robert Burton
Octopus, Bandung International School, Bandung, West Java, Indonesia
Through the eye of an octopus by Eric Scigliano, Discover Magazine
Q: How far away from earth does the space station travel and at what speed?
Vivienne, Adelaide, South Australia
A: The International Space Station averages 230 miles (370 km) above Earth,
and flies at 17,500 mph (28,200 km/h).
Further Reading:
Spotting the Space Station, WonderQuest
Q: Why is the most recent data on the average weights of Americans so
outdated, when Canada's information is current to 2005? Ezell, San Antonio,
Texas
A: A: The USA government schedules its comprehensive tests (HANES studies)
about five years apart. I asked USA Public Affairs Specialist
Mary Jones of the
National Center for Disease Control when data from the next study will be
available. "It is in the collection stage; we don't have a release date as yet,
maybe some time next year," she said.
The Canadians collect their data "every two years," says statistician
Heather Orpana of Statistics Canada in Ottawa. "We will have another survey in the field
in 2007/2008, which will also be collecting measured height and weight data."
Further Reading:
Women
sizes: British, USA, Canadian and Mexican, WonderQuest
Body
measurements, National Center for Health Statistics
Statistics
Canada
(Answered Feb. 19, 2007)
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