Click here for the page with thumbnails for pictures Cardisoma carnifex Family

Family : Gecarcinidae

     (only 1 species present in Seychelles)

   Genus : Cardisoma Latreille, 1825

     Species : Cardisoma carnifex (Herbst, 1794)

Cardisoma carnifex

Scientific name :Cardisoma carnifex (Herbst, 1794)
Creole name :Tyangomon
Family :Gecarcinidae
Distribution :
Seychelles :Mahe, Praslin, La Digue, Coetivy, Aldabra, Aride (Anderson, 1994)
World :From the Red Sea to Natal, Andamans, Japan, Taiwan and Polynesia (Vannini and Valmori, 1981b).
Ecology :
Habitat :Mudflats near mangroves. Juveniles live more inland than adults.
Mangrove and mudflat on La Digue - Union Estate
Mangrove and mudflat on La Digue - Union Estate, typical habitat for Cardisoma carnifex
Behind Beau Vallon
Mudflat at Beau Vallon, just before sunset
Diet :Herbivorous : rotten leaves, sometimes cannibalistic
Activity :Nocturnal, are more active during high tide
Influence of the moon cycle :It was observed very clearly that crabs were active (left their holes) during new moon and especially not during full moon. It was possible that feeding behaviour could have an influence on their relative condition factor. For this, the relative condition factor (real weight/estimated weight)*100 according to the formulas given under Size was set in a graph related to the moon cycle (figure 2). You can see that there is no strong relationship or influence.
Figure 1 : Influence of the moon cycle on the relative condition factor of the crabs
Burrowing :

Crabs hide in their burrows during the day. Burrows are larger and deep (probably as deep as the ground water level at low tide). Feed is taken into the burrow, maybe to allow decaying to improve the digestibility.
Description :
Size :The second largest land crab in Seychelles, after the Robber Crab. Carapax width of males can go up to 125 mm (largest cheliped : 120 mm). Carapax width of females can go up to 110 mm.
In Figure 2, you find the relationship between carapax width and weight of 63 crabs (32 males and 31 females), caugth at Beau Vallon between 7 and 9 pm
Figure 2 : Relationship between carapax width and weight
The lines for Est. Males and Est. Females are estimates of weight according to the following formulas :
Males : Weight=0.025057*(Carapax width)2.12, STDEV=50.9
Females : Weight=0.136*(Carapax width)1.71, STDEV=37.8
Morphological remarks :Carapax greatly convex with indistinct regions (Vannini and Valmori, 1981b). Juveniles (less than 50 mm carapace width) still have edges on the carapax
Colour :Carapax dark brown on top to yellowish brown on the sides. Legs greenish brown. Chelipeds yellow to white on fingers.
Differences in sexes :Adult males are larger and heavier (sea figure) than adult females and have more dimorphism between the 2 chelipeds.
Handedness :
Right handedLeft handed Total nr
Females48.9 %51.1 %45
Males32.7 %67.3 %49
Pictures :Cardisoma carnifex
Reproduction :Gravid females carry their eggs untill they hatch. Eggs are dark blue. Once I observed a gravid female eating some leaves. They go to the seaside to release the larvae. Some females drown doing this.
Fecundicity : I counted 425000 larvae on one occasion when I kept a gravid female untill hatching.
Cardisoma carnifex, berried female
Cardisoma carnifex, berried female
Juveniles :Juveniles don't show the 'blown-up' round shape of the carapax, but have a more rectangular, sharp edged carapax (see picture). They are mostly found further inland than adults.
Cardisoma carnifex juvenile
Cardisoma carnifex juvenile

Cardisoma carnifex
Large male Cardisoma carnifex

Cardisoma carnifex
Large female Cardisoma carnifex
Photo from J.Poupin : Crustacea Decapoda and Stomatopoda of French Polynesia

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