For decades there has been debate over whether or not there were two or three species of these crabs, which live tucked among the feathery ‘leaves’ of sea pens. They look almost identical, so you may never guess there were subtle clues in their claws, spines and even their DNA that told a different story.
By combining genetic analysis with a careful study of physical features, researchers have now confirmed two new species: Porcellanella brevidentata and Porcellanella longiloba. Both are found in northern WA, including the Ningaloo and Montebello Marine Parks, living symbiotically with sea pens in waters to around 120 metres depth.
Porcelain crabs are filter feeders, sweeping plankton from the water with specialised feathery mouthparts instead of using their claws to pinch and tear food. Living on a sea pen gives them both protection from predators and a raised perch to catch food drifting in the current.
While the benefits to the sea pen aren’t known, sea anemones that host other porcelain crab species are known to absorb nutrients such as ammonia, sulphur and phosphorus excreted by the crab. Because these crabs all share the same hosts and lifestyle, distinguishing between species has been challenging — until now.
This study has also cleared up questions about the identity of Porcelanella triloba. Specimens from Queensland and Western Australia have now been confirmed as distinct from the south Asian species Porcellanella picta, with which they had long been confused.
Alongside the description of two new species in WA, these findings suggest there may be more hidden diversity in the genus Porcellanella still waiting to be uncovered across the Indian and Pacific Oceans.
This discovery is also great example of how science often works in practice: Collections re-examined with new tools, assumptions tested and, sometimes, books re-written when the evidence demands it.
Read the research paper, now published in Ecology & Evolution: https://doi.org/10.1002/ece3.72131
