Nervous System
Decapods are highly complex invertebrates which have well developed sensory organs due to their active lifestyle. Branchyurans are the most evolutionary advanced crab group and display complete cephalisation of their nervous system. Anomurans are slightly less advanced and have intermediate cephalization, (Ruppert, Fox & Barnes, 2004.)
The main brain in hermit crabs is the supraesophageal ganglion, located just above the mouth and under the base of the eye stalks. Important major nerves radiate from this ganglion, including the antennular, optic, and other sensory nerves. This brain is connected to another brain, the thoracic ganglionic mass located more ventrally. These two ganglion are connected by the esophageal connective, which forms a ring around the esophagus to bypass it. The paraesophageal ganglion, another neurological region, is located around this connective ring that surrounds the esophagus. The ganglia in hermit crabs are not just limited to the head. Pairs of ganglia are found at the base fourth and fifth pereiopods, in the first pleomere, and five pairs are found along the length of the abdomen, (see Figure 19)(Tudge, Asakura & Ahyong, 2004.)
Figure 19- Diagram of the ganglia of the Blue striped hermit crab (Source: diagram modified from Tudge, Asakura & Ahyong, 2004, by Author, 2014)
Chemosensory organs are located on the legs, antennulae and mouth parts of hermit crabs, (Tudge, Asakura & Ahyong, 2004.) They are extremely important for finding food, and recognising members of the same species for sexual purposes. In order of these setae to remain in peak functional condition many crustaceans clean them, (Ruppert, Fox & Barnes, 2004.)
The Blue striped hermit crab has a set of compound eyes upon stalks. Stalks allow a larger field of vision, especially one which would be greatly reduced by a large shell, (Ruppert, Fox & Barnes, 2004.)
They also have a well developed statocyst located at the base of the antennular segments, one that not only tells the animal which orientation its body is but also the acceleration of its direction. This is something that complex vertebrates are able to do, but using their inner ear, (Tudge, Asakura & Ahyong, 2004; Ruppert, Fox & Barnes, 2004.) |