Lissocarcinus is a genus of Crabs from the Portunidae family known as the Swimming Crabs and containing nine species. Amongst them are two of our photographer’s favourites, the Harlequin Crab Lissocarcinus laevis and the Sea Cucumber Crab Lissocarcinus orbicularis.
Both highly photogenic, those two species are remarkably similar but easily differentiated by the nature of the host they are inhabiting.
What do Harlequin Crabs look like?
Lissocarcinus laevis, is commonly called by divers & photographers the Harlequin Crab, Harlequin Anemone Crab or Harlequin Swimming Crab. They were first described by Edward J. Miers in 1886 in the Celebes Sea, south of Mindanao but are widely spread throughout the Indo-Pacific until Japan and Hawaii.
It has a reddish, light brown carapace with large white to yellow spots and markings which are often interconnected. Its claws are banded with white and brown bands. The females are slightly larger than the males and can grow to a width of about 4cm with a body wider than it is long.
It has whitish, translucent legs with a characterized flattening of the fifth pair into broad paddles which are used for swimming although it is very rarely seen swimming.
Where can Harlequin Crabs be found?
Despite their bright pattern, Harlequin Crabs are hard to spot due to their size and living habits. Indeed, this crab lives in association with mushroom corals, tube-dwelling anemones and other types of sea anemones. Hiding under their mantle, tentacles or at the base of the tube, they are difficult to see unless you know where to look. They can be found on shallow reefs, sea grass beds, wherever their hosts are.
Around Amed and Tulamben, it is more commonly seen living in association with Sea Anemones from the Actinodendron spp known as tree anemones or hell’s fire anemones. Most sea anemones species are harmless to humans, but as its name suggests, some of those anemones are highly venomous and their stings can cause severe and painful skin ulcers. Caution is therefore to be taken while observing or photographing the Harlequin Crab.
This is a shy species and it will circle around the base of the anemone to hide from predators (and photographers). If threatened it will even retreat into the sand from which the anemone is growing.
Free loader or not?
Despite this symbiosis being very common throughout the Indo-West Pacific Oceans, very little is known about how the relationship works and whether benefits to both species are equal or unequal.
As for now their relationship is described as commensal meaning one species gains benefits from the relationship while the other neither benefits nor is harmed. In our case, the crab is receiving shelter and potential food from its host while not harming or affecting it in any ways.
Harlequin Crabs are predators and eat mainly shrimps and other tiny planktonic organisms. Scientists believe it could be also feeding on parasites from its hosts or even the host itself. But no studies have been done yet to prove so.
What about their bebes?
As with most crustaceans, the eggs are fertilized by the male and are carried under the body of the female. Orange at first, they turn to darker brown. Hatching occurred in 10-12 days after spawning.
Once they hatch the larvae go through a planktonic stage before settling down and growing into their adult form. The female crabs normally laid a new batch of eggs in 2-3 hours after larval hatching.
However, there isn’t any scientific publication on how females and males find each others… As they live on a host and usually one individual at a time, finding a partner must be an adventure!
Due to their pretty features, they are becoming prized by the aquarium trade but have yet to be bred in captivity.
When and where is the best to spot them?
We recommend diving during the day on the muck dive spots around Amed & Tulamben. We particularly love to photograph them on the shallow sea grass beds for maximum light and colors.
As they are found within 5m depth in those habitats, make sure you choose a calm day to go. Best time of the year would March to June and September to November when the conditions around Amed are the calmest and viz at its best.