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Eating - eversion and emesis

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Gray
155342.  Fri Mar 09, 2007 10:58 am Reply with quote

Q: What's quite interesting about the way that sea-stars, spiders and bluebottles eat?

A: They do most of their degestion outside their bodies.

Sea-stars (the less misleading name for 'starfish') generally have two stomachs. One stomach they pull out using an arm and lay it over their food, especially coral, and from which digestive juices flow and get to work on the tasty polyps. When they've reduced it to mush, the everted stomach is brought back in with the goo, which it passes to its second stomach which polished off the meal.

The all-time heavyweight in this area is the Crown of Thorns starfish, which looks, unconfusingly, like a crown of thorns:



It climbs onto almost any coral, exuding stomach acid from its everted stomach, eating away at the Calcium Carbonate 'shell' of the coral polyps, and breaking them down too. In the 1960s and early 70s, there was a frightful plague of them that took out most of the coral off Australia, Mauritius, Micronesia and the South Pacific. Then they just disappeared.

Reasons are unclear as to why this happened, but the overfishing of triton (the CoT's main predator) shells by locals to sell to tourists is thought to be very likely. A triton:



Spiders are all venemous, and all have hollow fangs of one size or another, through which they can inkect poisons and digestive juices into their hapless victims. The digestive juices do their work, and the spider, not having any chewing mouthparts, sucks back the tasty 'milkshake' through its fangs.

http://nationalzoo.si.edu/Support/AdoptSpecies/AnimalInfo/Tarantula/default.cfm

Houseflies have no chewing mouthparts either, and so much perform a similar trick. They vomit their stomach juices onto the food which they wish to digest, then presumably stand around whistling for a while. they then suck it all up again with a picturesque variety of mouth parts:



Sources:

Eating: http://www.gov.mu/portal/sites/ncb/moa/farc/amas2003/pdf/p4.pdf
http://www.vsf.cape.com/~jdale/science/digest.htm
http://www.globalcoral.org/corals_and_coral_reefs.htm
CoT Plague: http://www.aims.gov.au/pages/reflib/cot-starfish/pages/cot-q20.html

 

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