The Halloween Hermit Crab (Ciliopagurus strigatus) is also known as the Cone Shell Hermit Crab, the Striped Hermit Crab and the Orange Legged Hermit Crab. They are one of the more colourful smaller hermit crabs.
Hermit Crabs spend their lives in empty gastropod shells and as one of their common names implies, the Halloween Hermit Crab has adapted to the shape of Cone Shells and they are usually found in these shells. They are not that commonly seen in Tanzanian waters but that may be a function of their relatively reclusive nature. One sees many cone shells on the substrate but because of the dangers of touching these shells one leaves them alone.
Halloween Hermit Crab as their name implies, are brightly colored having bright orange legs that have red and grey bands on them. Similar to the spiny lobsters they have two sets of orange colored antennae, one short pair in the middle with sensory organs on it and the other longer and extendable outwards. The eyes and eye stalk are also orange colored. Normally only the legs and head are seen protruding from the shell but on occasion the top of the carapace which is white in colour protrudes.
The first set of legs has claws, and these have evolved to life in cone shells , being used as a barrier to seal themselves into the shell when threatened. The second and third legs are used for walking. The rear of the body is adapted to fold into the shell. The Halloween Hermit Crab grows up to 60 mm in width although in the wild most seem smaller .
HALLOWEEN HERMIT CRAB IN THE WILD
Halloween Hermit Crab are only usually only seen during daylight and we have never seen them out at night in Tanzanian waters. They usually move into hiding or will retract into their shell when they see a diver.
As with all crustaceans they molt at regular intervals and grow in size and their exo skeletons are very soft making them vulnerable to predators. On each molt they need larger shells which are often in short supply. There can be quite some urgency to find a larger shell after molting and they will actively fight over shells, with larger crabs going as far as pulling a weaker crab out of its shell using its claws.
The Halloween Hermit Crab are found on coral, rubble areas and rocky reefs across the Indo Pacific area from the African coast across to southern Japan and south to Australia. They are usually found shallower than 15 meters and we have not seen any deeper than this.
Halloween Hermit Crab are omnivores and eat detritus, algae and meat and scavenge as well.
The Males chemically detect when a female is fertile and approach them, often holding onto the female until she is ready to mate with them. Once the eggs are fertilised they are kept on the underside of the female inside their shell. When the eggs hatch the larvae are planktonic until they are large enough to find small shells.
They is some dispute over whether they are reef safe or not and whether they can fulfil an algae eating function in reef tanks. One can read a good article on this here. They are easy to feed and will devour large amounts of food. Given that the long term survival rate of Hermit Crabs in tanks is not good, one has to question whether they should be in a tank in the first place.