Decorator crabs are known to cover themselves with materials from their environment to hide from predators.
At Underwater World Singapore, however, visitors will not find the palm-sized crustaceans concealed by seaweed and corals - at least not till Christmas is over.
Instead, the crabs have covered themselves with baubles and stars.
Because of the festive season, Underwater World Singapore, which is in Sentosa, has designed the enclosure of its decorator crabs to resemble a winter wonderland.
Animal and nature groups, however, are not cheering. They say the re-created enclosure is artificial and detracts from the crabs' natural environment.
Ms Selina Sebastian, deputy executive director of the Society for the Prevention of Cruelty to Animals, notes: "Re-creating their environment by placing Christmas ornaments for the crabs' use interferes with their natural environment and makes it artificial. The ornaments are not necessary as they do not add value to the camouflage process."
Adds Mr Tan En, 30, director of advocacy at the Animal Concerns Research and Education Society: "Enclosures for animals in captivity should be as natural as possible. This can help members of the public understand and learn about the animals' natural behaviour."
Mr Stephen Beng, 45, chairman of the Nature Society Singapore's marine conservation group, feels that presenting the crabs in this manner is undignified.
He says: "Let's hope the crabs don't see their own reflections during Christmas. Just as some people like to dress their pet dogs in clothes and shoes, wild animals in captivity are at the mercy of the people who care for them.
"In this case, it is done solely for the pleasure of visitors and has no benefit to the animal."
Underwater World Singapore declined to comment on the feedback from the groups.
But in a press release issued last month on the enclosure's re- design for the holidays, its marine biologist April Rose Obial explained that the attraction's curatorial team made sure the ornaments are of a suitable size for the crabs to carry around.
She added that decorator crabs also "decorate" themselves using man-made items that are washed out to sea, such as clothing. These accessories are attached to the hooked hairs lining the crabs' shells.
Underwater World Singapore has been exhibiting decorator crabs, which can be found worldwide, since 2005.
Professor Neil Cumberlidge from Northern Michigan University, who is the chairman of the freshwater crustacean specialist group of the International Union for the Conservation of Nature Species Survival Commission, sees no harm in the crab enclosure being decked with Christmas decorations.
"I think it will focus more public interest on crabs which, from my point of view, is a good thing," he says. "In captivity, there are no predators so any loss of concealment by using Christmas colours will not be detrimental to the crabs' survival."
Says Mr Naryan Goyal, 30, a tourist from India who saw the crabs last Wednesday: "I don't see anything wrong with this re-design. The crabs do not look like they are suffering."
Apart from the enclosure's re-design, Underwater World Singapore has a Play Like A Child promotion for Singaporeans and local residents where adults pay the child rate of $20.60 each for admission.The deal is valid till Jan 3.