Nervous System
The nervous system of cephalopods is highly complex and has allowed them to adopt an active predatory lifestyle. Numerous ganglia are concentrated into a cephalised brain, protected by a cartilaginous cranium, which is larger in relation to body size than that of fishes (Ruppert et al. 2004). The small squid, Pickfordiateuthis pulchella, has a mantle length of approximately 21mm (similar in size to I. notoides), and a CNS with a volume of approximately 2.4mm3 (Nixon and Young 2003).
The brain of adult extant cephalopods surrounds the oesophagus and is divided into bilaterally interconnected regions. The supraoesophageal mass controls sensory input and integration and the suboesophageal mass is responsible for motor control. These are further divided into many, typically bilaterally symmetrical brain lobes, including paired optic lobes that are adjacent to the eyes (Ruppert et al. 2004; Wollesen et al. 2010). Behavioural evidence has suggested that cephalopods can evaluate memory input and focus attention and this has lead to the idea that they may have a form of primary consciousness (Mather 2008).
The emergence of this large and complex nervous system in cephalopods is an example of the convergent evolution they share with another group of active and intelligent animals, the vertebrates (Wollesen et al. 2009). However, knowledge of the cellular and molecular processes that produced this complex CNS in cephalopods and its ontogeny in living animals is lacking (Wollesen et al. 2009; Wollesen et al. 2010). |