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Menaethius monoceros

Spider crab, Decorator crab

Chi Chiu Lo (2014)



Fact Sheet


Brief Introduction


Physical Description



Relationship With Other Organisms

Life History & Behaviour

Anatomy & Physiology


Biogeographic Distribution

References & Links


Internal transport system
The internal transport system of crabs is the hemal system that there is hemocyanin, a type of pigment, which is responsible in transporting oxygen within the hemal system (Ruppert et al. 2004). And the movement of liquid in the hemal system is powered by the beating of the heart (Ruppert et al. 2004).

Respiratory system
The gill chamber contains gill pairs that are attached to the coxa (Ruppert et al.2004). Water enters the chamber through the inhalant apertures powered by the gill bailer (Ruppert et al. 2004). Then, there is ion and gas exchange between the blood and water (Ruppert et al. 2004). Water finally leaves the chamber through exhalent apertures (Ruppert et al. 2004).

Digestive system
Crabs have a complete gut, which mean its digestive system has two opening, one for ingestion and the other on for excretion. The mouth part of crabs consists of a few pair of appendages including maxilllula, maxilla, mandibular and maxillipeds, that the anterior part of the mouth prevents refluxing of ingested food by hard labrum reinforcement (Ceccaldi 1998). The fore and hind stomach of crabs is associated with chitinous and proteinous complex. The chitin layer actually serves as part of the exoskeleton and would be replaced by a new one during molting (Ceccaldi 1998). There are also calcified structures in the stomach help grinding the food particles (Ceccaldi 1998). Other than physical digestion, the digestive track of crab also secretes a series of enzymes for breaking down food particles chemically (Ceccaldi 1998). Moreover, the digestive system of crabs can also act as a nutrient reserve when there is deplete of food (Ceccaldi 1998).

Menaethius monoceros has very thin andpointy legs other than broad and flappy legs is because of its locomotion style. Most of the time, it walks on the substrate of the bottom, including coral, seaweed and cyanobacteria mat. Thin and pointy legs decreases the surface area that the legs actually contact with the surface of the substrate,which it allows the crab to walk faster.