Changi Beach produced many new sightings for me, including my first seahorse, sea pencil, spiny sand star, various sea urchins and the backside of an acorn worm. One animal that also cropped up in past reports is the moon crab and towards the end of the outing my despondent duck was feeling sore at not seeing a single Matuta Ashtoret lunaris until Ron found this fellow languishing on a thick pile of Ulva. It was probably in the wrong place at the wrong time and made no effort to flee. In any case, its paddle-like pereiopods are not made for walking and the thick mesh of seaweed offered no way for it to swim out. Typically, the moon crabs are found on sandy bottoms where they emerge at night to feed on other animals. Smaller individuals catch copepods and other tiny crustaceans while adult crabs eat anomurans (hermit crabs) and snails. When disturbed, they are able to rapidly bury themselves backward in the sand at a steep angle. Unusual respiratory modifications allow moon crabs to breathe even when buried deeply without any contact with the surface of the sediment, helping the animal survive for up to 4 hours in moist shore sand during low tide periods.
Moon crabs were once regarded as members of the family Calappidae although some have questioned this classification and now rank them in their own family, Matutidae. And if you were wondering, Matuta is the Greek goddess of dawn, and the crabbygirl informs me that the crab in question is now reassigned to the genus Ashtoret to honour a Canaanite deity. The difference lies in the ridge on the outer surface of the cheliped, which if oblique signals Matuta and is straight for Ashtoret. Male moon crabs mature at a larger size (43 mm carapace width) than the females (37 mm) and breeding is reported to occur year-round, with each female capable of producing multiple batches of eggs from one copulatory session, with each batch numbering up to 65,000 eggs. In some countries, they are eaten by humans, but fortunately for them, carcinological culinaires around here prefer far larger carapaces. We lifted the little moon crab up for a quick mugshot before placing it on a sandy patch where it might shuffle its way in to flee the glare of the sun.
Actually, this species is no longer in the genus Matuta. It's name is Ashtoret lunaris (Forskal 1775).
Also, some recognise Matutidae as a family in its own right as opposed to sub family. Oh wait.. that be me then. I have to write up a paper on it. When I am done with pelagicus.
Posted by: tgwttihs | 05 July 2007 at 03:32 PM
Forgot to reference.
Galil and Clark 1994 (A revision of the Genus Matuta Weber, 1795 (Crustacea: Brachyura: Calappidae))
Posted by: tgwttihs` | 05 July 2007 at 03:36 PM