Many species don't have anything to be thankful for this holiday season. Here's one that may have already been lost.

Species name: The Christmas Island shrew (Crocidura trichura)

Where found: This miniscule mammal only exists—if it still exists at all—on Australia's Christmas Island, a tiny dot in the Indian Ocean that is also home to a number of other unique species, most notably the Christmas Island red crab (Gecarcoidea natalis), which famously swarms over the local beaches every year.

IUCN Red List status: Critically endangered (possibly extinct). The shrews have not been seen since at least the 1980s.

Major threat: No one is sure exactly why the Christmas Island shrew disappeared. It could be tied to the arrival of the yellow crazy ant (Anoplolepis gracilipes), which also threatens the red crabs and has been linked to the recent extinction of the Christmas Island pipistrelle bat (Pipistrellus murrayi). Other factors that may have influenced the species' decline include habitat loss, other invasive species such as rats and cats, and road traffic. (Unfortunately the shrews were not recognized as a separate species until 2005, which may have delayed conservation efforts.)

Notable conservation programs: None, unfortunately. There's an official species recovery plan in place, though, just in case the shrews ever show up again. Sadly, that seems like it would require a Christmas miracle.

Photo: A 2011 stamp depicting the Christmas Island shrew, via the Universal Postal Union