True Colours

A brachyuran of the Hirsutodynomene genus, found on Ningaloo Reef.
Image: Gary Cranitch


20 May 2010
It's not easy being green, or purple, orange or blue – at least if you're a crab and you happen to catch the eye of University of Singapore Ph. D. student Rob Lasley.
Rob is studying brachyura, or true crabs, focusing on the xanthid family, specifically the genus Chlorodiella.
With about 7,000 known species, true crabs are a diverse group. Rob says that it is challenging to classify new species definitively in the field, because many of the features that distinguish species from each other can only be found through detailed lab work.
"It's hard to tell because they're small, but look at this one," Rob urges. "It's blue and purple and the claws are orange and it's got hairs all over it. From a distance it looks just like this one, but this one is totally different: the shape of the carapace (the shell) is different and it's got different colour spots on it. Colour is very important," he says.
"We also look under a microscope at the small structures: the tips of the claws, the teeth on the side of the carapace, and in males, the intermittent organs for mating, called gonopods," he says.
Following extensive lab work on the crabs he collected in Ningaloo on last's year CReefs expedition, Rob is certain he has discovered at least one new species of Chlorodiella. Chlorodiella are characterised by rounded, often called spoon-shaped, tips on the claws. Rob is collecting more samples on this trip.
"I've found species of Chlorodiella on all the CReefs trips: in Ningaloo, Heron Island and Lizard Island. It's amazing that a species can be found all over the Indian and Pacific Oceans, yet we know so little about it. It shows how much we still have to learn about the biodiversity of coral reefs," Rob says.
Rob says he is fascinated by the diversity of crabs.
"And," he adds, "they're fun to catch."