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).
|