Once I Explored Are There Crabs Evolving To live Entirely On Land?

if you are interested in evolution of land crabs first find a book on invertibrate zoology with LOTS of examples and lots of pictures and descriptions of the physiology and behavior of all these critters. here is one:

Animals Without Backbones (Hardcover)
by Ralph Buchsbaum, Mildred Buchsbaum, John Pearse, Vicki Pearse

http://www.amazon.com/gp/product/0226078736/002-9871747-0573642?v=glance&n=283155


realize that there are over 100 different families of arthropods(insects, spiders, scorpions, sowbugs, millipedes, crabs, shrimp, krill, copepods...) each with it's own lifestyle!

there are loads of different crabs:

some climb trees and crack open coconuts:

birgus latro

http://www.arkive.org/species/GES/invertebrates_terrestrial_and_freshwater/Birgus_latro/

This species is a type of land hermit crab with a spectacular appearance and intriguing biology. It is probably the largest terrestrial arthropod in the world and is able to grow to relatively gigantic proportions. Unlike most other hermit crabs, only the juveniles of this species find and use gastropod shells for protection as they develop. Adults have abandoned the shell-carrying habit, and instead have hardened shells over the abdomen. This protects the crab, reduces water loss and does not restrict its growth, allowing it to reach up to a metre in size. This huge crustacean is well adapted to life on land with long strong legs. It also has large muscular claws which are used for punching holes in coconuts and scooping out the flesh. This is a unique behaviour amongst crabs and explains why this species is called the coconut crab. The claws are in fact so powerful they can lift objects such as vegetation or rocks weighing up to 28 kg. Its stalked eyes are red, and this crab�s body colour varies between islands from purplish-blue to orange-red. Studies show that males are considerably larger than females.

here is a video of coconut crab cracking open a coconut!

http://www.arkive.org/species/GES/invertebrates_terrestrial_and_freshwater/Birgus_latro/Birgus_latro_00.html?movietype=rpMed





and look at these guys! < blackskimmer > 03/03 12:36:25


they keep water in their shells, which they collect from dewdrops rain puddles etc... to keep their efficient gills moist and breath in the AIR. they however goto sea to realease eggs. the larvae develop in the sea:


The Caribbean Terrestrial Hermit Crab Coenobita Clypeatus (herbst, 1791)

http://www.fmrpets.com/promotions.ivnu


here is another family of terrestrial crabs:

pics:
http://www.geocities.com/ericdemuylder/gecathum.htm

http://www.geocities.com/ericdemuylder/index.htm



the level of detail, and kinds of details you want, to ask can these buggers evolve to be truly land critters:
Osmoregulation in the terrestrial Christmas Island red crab Gecarcoidea natalis (Brachyura: Gecarcinidae): modulation of branchial chloride uptake from the urine

H. H. Taylor1,* and P. Greenaway2

http://jeb.biologists.org/cgi/content/full/205/20/3251



can crabs escape ENTIRELY from the sea? look: here are freshwater crabs that breed OUT of the ocean, and are on their way to breeding entirely on land:

REPRODUCTION IN THE FRESH-WATER CRAB CANDIDIOPOTAMON RATHBUNAE (BRACHYURA: POTAMIDAE) IN TAIWAN
Hung-Chang Liu,a and Chia-Wei Lia
http://0-www.bioone.org.library.lib.asu.edu/bioone/?request=get-document&issn=0278-0372&volume=020&issue=01&page=0089

note:

"The reproduction of fresh-water crabs differs from that of marine crabs. Eggs of fresh-water crabs are large and yolky, and hatch directly into young crabs rather than free-swimming larvae. The hatched crabs are brooded by their mother under her abdomen for several days before they are released (Ng, 1988). In some cases (e.g., Metopaulias depressus Rathbun), highly developed larvae emerge from the eggs and complete their development in fresh water (Diesel and Schuh, 1993)."



these babies are on their way to hatching fully terrestrial young without any water needed at all! kind of like what mammals and some toads do.




crabs can spend their ENTIRE lives in trees: many aquatic critters live in water filled tree holes, or water filled bowls of the plants called bromeliads:

more mother crabs caring for young in bromeliads:

http://bromeliadbiota.ifas.ufl.edu/crbrom4.htm

Crustacea in Bromeliad Phytotelmata

Wolfgang Janetzky
Carl von Ossietzky Universit�t Oldenburg,
ICBM - AG Aquatische �kologie,
D-26111 Oldenburg, Germany

http://bromeliadbiota.ifas.ufl.edu/crbrom.htm




crabs dropping in shells to adjust pH water: < blackskimmer > 03/03 12:44:26


The East Usambara tree-hole crab (Brachyura: Potamoidea: Potamonautidae) - a striking example of crustacean adaptation in closed canopy forest, Tanzania
J. Bayliss
Abstract

An undescribed species of freshwater crab with a remarkable life history was studied over 2 years in areas of natural forest in the East Usambara Mountains, north-east Tanzania. It was found occupying the water-filled boles (tree holes) of several tree species at altitudes between 150 and 900 m asl, a single tree species Myrianthus holstii accounted for 26% of all trees identified as such. There was no apparent association with other freshwater bodies. The 'tree-hole crab' is largely nocturnal but will also forage by day during periods of heavy rainfall, leaving its tree hole in search of leaf-litter molluscs. Once located it carries pieces of the snail shell back to the tree hole and releases these into the water filled bole which is typically acidic. This releases calcium ions (Ca2+) into solution from the snail shell resulting in a more neutral solution (mean pH = 6.6, standard deviation (s) = 0.46, n = 25). This act provides a source of dissolved calcium for the development of exoskeletons following ecdysis. Significant differences were found between depth (P = 0.01) and height (P = 0.05) of occupied and unoccupied water-filled tree holes. This is the first record of a crab exhibiting such behaviour in East Africa.


http://www.blackwell-synergy.com/doi/abs/10.1046/j.0141-6707.2001.00333.x




wow, you really love crabs < uknoit >

i love all bursting with inventiveness biology < blackskimmer >

the point is before talking about evolution, gather up LOTS of examples. that's why Darwin went on a 3 year long voyage and then waited 25 years to publish his conclusions.

p.s. i had only VAGUE notions that these critters existed before i just hunted them down for the original poster. i had NO idea that there was a crab that CRACKED open coconuts!