|
August 24, 2004
Shell game
Whoa! I just realized that I almost forgot to post any pictures from my trip. Here's one which expresses my mood perfectly: Frankly, looking at that picture makes me jealous! These little critters don't have to worry about elections; they can just tuck themselves into their shells. Well, maybe not "their" shells in the strictest sense, but when the original owner dies or gets eaten, why let a perfectly good shell go to waste? So what if it's pre-owned? And once you outgrow the shell, you just find another one, and leave the last one behind for some other deserving hermit. They get pretty big too; while I was SCUBA diving I saw one inside a large conch shell. (Well meaning humans even make designer shells for their captives.) The guys in the above picture are Caribbean Land Crabs -- Coenobita clypeatus. They have gills, but use them as lungs by means of a curious adaptation: As an adaptation for extracting oxygen from the air rather than from the water, the gills of Coenobita are reduced in number and stiffened, and the inner walls of the gill chamber are vascularized to promote the exchange of gases. Also, ventilation of the gill chamber is enhanced by the reduced side walls of the carapace or head shield of the crab. Moistening of the gills is abetted by well-developed glands in the bronchial region.Gills as lungs? It may sound unnatural to some, but they've been doing it so long that in captivity they can be terrified of water. Yup; well-meaning owners can kill them by just by giving them a bath. That's because their shells hold water in just the right balance for the crabs: The danger of drying out or of over concentrating the body fluids through evaporation is the most critical problem confronting any animal that migrates from water to land. Coenobita has an advantage in this respect over the true land crabs, for it can store water in the appropriated snail shell, and this water may be used secondarily for drinking. One reason that hermit crabs so frequently try on different abandoned snail shells is to find one that fits the delicate abdomen closely, thereby minimizing evaporation. The same explanation probably accounts for the nocturnal habits of Coenobita Clypeatus in the southern part of its range, where daytime activity could result in severe evaporation. Experiments have shown that animals in well-fitting shells can subsist without food and water six times as long as those removed from their shells. When the crab withdraws into its shell in the daytime, the claws and walking legs form a reasonably effective seal in the shell mouth against evaporation. The parts of the animal that protrude farthest from the snail shell are most heavily calcified, and this undoubtedly helps to prevent the evaporation of body fluids.While that's more than I really needed to know, I can't say I disagree with any of it. I'm all in favor of preventing adverse concentration of body fluids, although I have nothing against trying on new shells. NOTE: I don't mean to offend any crabs or hermits who might be reading this post. I'm a crab myself as well as a borderline hermit. posted by Eric on 08.24.04 at 05:04 PM
TrackBack
TrackBack URL for this entry: http://classicalvalues.com/cgi-bin/pings.cgi/1319 Listed below are links to weblogs that reference Shell game:
» Bonfire of the Vanities 61: I Love the '80s Edition from mypetjawa v. 2.0 (beta)
This week's Bonfire of the Vanities asks the blogosphere: Where were you in 1987? Forget the worst of the worst for the past week, this week's Bonfire spotlights the worst of the worst from 1987! A bad year in a... [Read More] Tracked on August 31, 2004 02:03 PM |
|
March 2007
WORLD-WIDE CALENDAR
Search the Site
E-mail
Classics To Go
Archives
March 2007
February 2007 January 2007 December 2006 November 2006 October 2006 September 2006 August 2006 July 2006 June 2006 May 2006 April 2006 March 2006 February 2006 January 2006 December 2005 November 2005 October 2005 September 2005 August 2005 July 2005 June 2005 May 2005 April 2005 March 2005 February 2005 January 2005 December 2004 November 2004 October 2004 September 2004 August 2004 July 2004 June 2004 May 2004 April 2004 March 2004 February 2004 January 2004 December 2003 November 2003 October 2003 September 2003 August 2003 July 2003 June 2003 May 2003 May 2002 See more archives here Old (Blogspot) archives
Recent Entries
War For Profit
How trying to prevent genocide becomes genocide I Have Not Yet Begun To Fight Wind Boom Isaiah Washington, victim Hippie Shirts A cunning exercise in liberation linguistics? Sometimes unprincipled demagogues are better than principled activists PETA agrees -- with me! The high pitched squeal of small carbon footprints
Links
Site Credits
|
|
Beautiful shells. Thank you.