Creature of the week
Half Crab
Petrolisthes elongatus
Maximum 18mm across the back plate (carapace)
The New Zealand half crab, Petrolisthes elongatus, is a species of porcelain crab found
around New Zealand, and the east coast of Tasmania. Its carapace width is up to 18 mm.
Description: Colouring is greenish-blue. “Oval carapace, claws are flat
and trangular, held close to the body, the antenae (feelers) are long and
whip-like which betray the fact that it is not a true crab!
Also, on turning the body over, there is a broad abdominal flap with a tail fin
– a true crab does not have these things ! * It is related to Hermit Crabs and
some lobster types.
Habitat:. The half crab (Petrolisthes elongatus) is one of our most abundant
species, literally swarms under intertidal stones.
Distribution: New Zealand and East coast of Tasmania,
Maximum Size: Carapace width up to 18 mm
Diet: Scavenger and suspension feeder crabs are opportunistic
omnivorous (eat plant material and animal protein) scavengers. The third
legs carry silky threads on the end, in the form of a strainer which catches
debris, both plant and animal that pass by on the current and pass them to the
mouth in a left-right sweeping motion.* The large claws are not used
directly in feeding, but are digging tools, working in the debris on the sea
floor and stirring up the material, so that the strainer gadget can catch the
disturbed goodies.
References
* From Morton/ Miller, “the N.Z.Sea Shore”


Woodbridge TasEd
Australian Government Department of Envioronment & Heritage
Read more: http://wiki.answers.com/Q/What_does_a_half_crab_eat#ixzz1eHiSdZer
Wikipedia Page
http://en.wikipedia.org/wiki/New_Zealand_half_crab
Related Websites
http://www.deh.gov.au/cgi-bin/species-bank/sbank-treatment.pl?id=78805,
http://www.woodbridge.tased.edu.au/mdc/Species%20Register/crabs.htm