Geosesarma notophorum (Mandarin crab) – Species database

[Ollie Mengedoht]

Text: Monika Rademacher,
Photographs: Oliver Mengedoht
Translation: Ulli Bauer

Scientific name: Geosesarma notophorum

Trivial name: Mandarin crab

Systematics: Domain: Eucaryota, kingdom: Animalia, subkingdom: Metazoa (multiple-celled animals), Eumetazoa (true tissue), grade: Bilateria, branch: Protostomia, infrakingdom: Ecdysozoa (molting animals), phylum: Arthropoda (jointed-leg invertebrates), subphylum: Crustacea, class: Malacostraca (higher crustaceans), superorder: Eucarida, order: Decapoda (ten-legged crayfish), suborder: Pleocyemata, infraorder: Reptantia, section: Brachyura (true crabs), superfamily: Grapsoidea, family: Sesarmidae (mangrove crabs), genus: Geosesarma, species: Geosesarma notophorum

Origin/range: Pulau Lingga, an island east of Sumatra (Indonesia)

   

More pics: http://www.panzerwelten.de/v/Geosesarma/..._mandarin/

Description: Variable coloration - as with most crab species. In general its body is light brown to brown with purple areas, especially the back end of the carapace shows a more or less blueish to truly blue color, depending on the light. The C-shaped groove in the middle is maroon as a rule. The majority of these crabs has bright green eyes, those of some specimens, however, are of a yellowish-green color, and some individuals even have yellow eyes. The claws are bright orange in color, the legs are more or less light brown to red.

Juveniles are beige to brown in color and do not have orange claws. Their green-yellow eyes are also less intensive in color, which is a good camouflage for the young brood until they reach sexual maturity (which happens probably when they've grown to 1 cm carapace diameter).

   

Sex differences: Typical for crabs, the males have a narrow apron, the females have a wider apron covering nearly the entire abdomen. The males' claws are bulkier than those of the females, and their right claw is slightly enlarged (not really discernible with the naked eye, though).

Size: Up to at least 11 mm carapace width.

Life span: About two years.

   

Temperature: Tropical (about 20 to 28 °C)

Tank size/stock: Starting at 40 cm length for a pair; keeping a small group is preferrable, however, in a tank from 60 cm upwards. The group should consist of more females than males, but also a stock of equal numbers of males and females ought to work out. There should never be more males than females in a group.

   

Tank set-up: Terrarium with a small water bowl; well-structured with various levels to climb on, hideouts and substrate suitable for burrowing; plants (also weeping ones), mosses.

   

Food:
G. notophorum seem to be omnivores, ours have up to now taken frozen food (brine shrimp, mosquito larvae, cyclops) as well as fish flakes, granules and fruit. It is recommendable to provide them with an additional source of calcium like cuttlebone or possibly ground eggshells or something along these lines.

   


Behavior: Relatively peaceful, like to sit at close quarters from time to time. All in all it can be said that G. notophorum live rather secretively and avoid brightly lit places. However, if their terrarium is lit with rather dim, subdued light they do come out of hiding every now and then. If they find predefined hideouts in their terrarium in the form of niches, nooks, leaves, mossy parts and so on they will gladly use these alternatives and show only litte ambition to burrow.

Reproduction: Specialized reproduction in fresh water with fully developed young crabs instead of larvae. The females carry 8 to 12 relatively large eggs (> 1mm) under their aprons, recent reports on keeping these crabs point to the possibilty of larger egg clutches, however. After the young crabs hatch they are carried on the females' carapace for two to three days - an up to now unparalleled brooding behavior observed in crabs.

Sociaization: .
This crab species is best kept in a dedicated terrarium.

   


Additional information:
• This species was first described by Peter K.L. Ng and Cheryl G.S. Tan in 1995, including the special brooding behavior, which has up to now only been known for this species.

   

• On Pulau Lingga this species lives at a height of 1,000 to 1,300 m above sea level - highland crabs. Their discoverers reported that these crabs can climb up for several meters in captivity without problems.

• Sometimes these animals also take to the water, but only relatively seldom and mostly not for too long a time. They prefer places that provide them with a direct possibilty to sit on so that primarily their legs are in the water, the body above, starting at the onset of the maxillipeds. This species does not seem to be able to drown, though!
   

• This species belongs to the group of Geosesarma malayanum of the genus Geosesarma (in which the exopod of the third maxilliped does not have a flagellum, the distant part of the first gonopod is short) - Ng has divided Geosesarma into three groups. This is not really astonishing if you consider that among Geosesarma there are also unspecialized reproductive types even though their exterior characteristics resemble the other species closely; those types reproduce in seawater and have several larvae stages. Then there are crabs of the abbreviated type in this genus, and also some of the completely abbreviated type, i.e. the development takes place inside the egg entirely and fully developed young crabs hatch. There are purely terrestrial species and various brood care types.

• The crab species Geosesarma krathing (orange crab - http://www.panzerwelten.de/forum/showthread.php?tid=464 ), brought into the hobby about two years ago, looks confusingly similar and can hardly be discerned from G. nothophorum. Even their morphological characteristics are not easy to detect. The eyes of G. notophorum, e.g., are larger than those of G. krathing, which makes them fit into the small child pattern better - the most striking difference, together with the legs mostly lighter in color. Moreover, G. krathing has a nook on the ischium of the third maxilliped (the most prominent external mouth part), G. nothophorum does not - see pic below. If their aprons also differ in some way is something we cannot say as we do not have any male G. krathing specimens.


G. krathing has a nook (colored green, on the right-hand side) on the ischium of the third maxilliped, G. notophorum does not. PHOTO: Chris Lukhaup/Crusta10

• According to Ng and Tan, after hatching the young crabs crawl over the onset of the mother crab's legs and its lateral part onto its back, where they are covered by the water film typical for the searmid's breathing system. Often the female can be found sitting under moist objects, probably in order to maintain a high humidity for its offspring. In the beginning, the young crabs sit quietly and start showing more activity after two to three days. Especially when they are about to leave their mother they can be observed crawling frequently over the mouth parts and the eyes of the mother crab. When the offspring are getting too active for it, the mother crab takes them in its claws and puts them down on the substrate. During the entire brooding time the females don't seem to eat at all (probably a genetically determined behavior that protects the offspring from being eaten by their parents).

In the beginning, the young crabs are red and attain a splotchy brown color after several molts, including their eyes. According to Ng and Tan the eyes only turn green or yellow when the crab has reached a carapace width of about 1 cm. This coloration provides them with good camouflage on a substrate with a dark surface color and dead leaves.