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The crustacean brain consists of three areas (Sandeman et al. 1993). Firstly, there is the protocerebrum, which can be divided into the optic ganglia, which innervates the compound retina, and the lateral and medial protocere-brum. These areas also innervate the frontal organs, sinus gland and muscles of the head. Secondly, there is the deuto-cerebrum, which contains the neuropils associated with the antennules. The olfactory lobes receive the total input from the chemoreceptors on the antennules, and also contain the motorneurons that control their movements. Finally, there is the tritocerebrum, which contains the tegumentary neuropil that receives the nerve fibres from sensory cells from the carapace and the neuropils that receive the inputs from the antennae motor- and mechano-receptors.

In the ventral nerve cord, the first ganglion (sub-oesophageal) and the remaining ganglia (from the thorax and abdomen) receive inputs from the sensory cells dispersed in the body and supply nerves to the muscles of the mouth parts, pereopods, pleopods and tail fan. In addition, the stomatogastric ganglia supply nerves to the oesophagus and the foregut (Bliss 1990).

Sandeman et al. (1993) surveyed the morphology of several decapod crustacean brains. They described the anatomy of the brain of M. novaehollandiae, which may be representative for other carideans. It exhibits well-developed olfactory and antenna neuropils. The antennular neuropils are smaller and subdivided. The olfactory lobes are linked to neuropils in the eyestalks by a large tract (Fig. 3.7b).

Another structure associated with the anterior part of the brain, is the organ of Bellonci, which in M. rosenbergii is located in the haemocoel in the distal part of the eye-stalk (Hallberg & Kauri 1992). From their investigations they suggest that this does not have a photoreceptor function but probably has a sensory role of some sort, perhaps more than one since two types of sensory cilia were described.

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