Nervous System

The brachyurans have a a highly modified nervous system compared to that of their other distant relatives in the decapods (Ruppert et al. 2004). High cephalization is seen due to their body plan of a reduduced abdomen. The joining of all the segmental ganglia to form one large ganglion known as the subesophageal or thoracic ganglion (aggregation of nerve cells, similar to a simple brain)(Ruppert et a. 2004).

Endocrine & Neurosecretory System

Currently the known endocrine glands found in Crustaceans are the Y-organ, ovary, sinus and androgenic gland (Ruppert et al. 2004). The Y-organ, located in the antenenary segment contains hormones that affect the rate of development (Knowles & Carlisle, 1956).  The sinus glands stops blood sugar levels from reaching a low level by excreting a diabetogenic principle, in crabs in appears the eye stalk also has some control over this also (Knowles & Carlisle, 1956).  The eyestalks play a very important role in both systems as it also houses hormones which control testicular growth, ovarian growth and water-balancing (Knowles & Carlisle, 1956).

The highly important moulting cycle is believed to be controlled by as many as six or a minimum of three different hormones (Knowles & Carlisle, 1956).  Found in the ganglion and eyestalk, the moult inhibiting hormone inhibits the period before moult, known as premoult. When premoult does occur it is the moult-accelerating hormone the determines the length of the phase (Knowles & Carlisle, 1956).  Both of the above mentioned hormones can act on the Y organ which produces an essential hormone to the process of moulting (Knowles & Carlisle, 1956).