Infra-order Brachyura, Family Gecarcinidea
The Christmas Island blue crab was originally known as Cardisoma hirtipes and was then later considered to be a unique colour form of the widely distributed land crab, Discoplax hirtipes.
Studies of museum and fresh specimens of Discoplax hirtipes across most of its range in the Indo-West Pacific and eastern Indian Oceans, as well as an extensive series of specimens from Christmas Island, showed that the Christmas Island blue crab is actually a distinct species endemic to the island. As of February 2012, it was known as Discoplax celeste.
Recent re-examination of the taxonomy of Gecarcinidae resulted in an unexpected outcome. A new genus Tuerkayana n. gen. was established to accommodate two species previously assigned to Cardisoma and two species previously regarded as Discoplax: T. celeste (Ng & Davie, 2012) n. comb. and T. magnum (Ng & Shih, 2014) n, comb.
The Christmas Island Blue crab is therefore now Tuerkayana celeste (Ng & Davie, 2012)
Christmas Island Blue crab | Tuerkayana celeste (Ng & Davie, 2012)
A large crab with a deep and rounded carapace up to 160 mm wide. Adults (carapace width 45 mm or more)
are overall blue to bluish-white. The legs and large claws are very pale blue to white colored. The legs have long coarse hairs on all sections. Dense mats of brown hair border both sides of the mouth parts in both sexes.The live color of the blue crab varies with maturity but is generally consistent with size.
Tuerkayana celeste is endemic to Christmas Island.
Blue crabs dominate wet areas. The blue crab has an association with, and a need for freshwater. It is therefore found in moist areas near permanent freshwater flows and seepages. Its distribution on Christmas Island is restricted to discrete populations on the shore terrace around the island.
More detailed and specific information on blue crab taxonomy, physiology and biology, their annual breeding migration, the affect of the introduced yellow crazy ant, with accompanying images, is presented in the book
"Crabs of Christmas Island" by Max Orchard