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Cephalopod brain size

cephalopod and veretbrate brain-body weight cephalopod and fish growth curves
A, Adult cephalopod brains compared with Jerison's (1969) size classes for higher and lower vertebrate brains. upward pointing triangle Sepia; downward triangle  Loligo; 1, Octopus vulgaris; 2. O. salutii; 3, O. defillipi; 4 and 5, oegopsid squids Illex and Todarodes. (Open symbols from data supplied by Mangold-Wirz.) B, Growth curves of the brain of the cuttlefish (triangle) (original), octopus (circle) (Packard & Albergoni, 1970) and various fish. (Herring, original; dogfish, Kellicolt, 1908; other fish Geiger, 1956)
 Fig. 1. Brain size and relative growth. Log plots of brain and body weights. 

"Weight for body-weight the modern cephalopod brain is in the same size bracket as the vertebrate brain (fig 1a), smaller than that of birds and mammals, but as big or bigger than most fish brains. Individual brain-body-weight growth curves of cephalopods and fish are also similar (Fig. 1b): the growth curves for the cuttlefish and the dogfish being, rather surprisingly, amongst the highest on the log-log scale.  Increases in the weight of the brain during post-larval life are of the order of 150-fold both for the octopus and the herring, and in both these species the total increase from hatching to adult is of the order of 5000-fold (Packard & Albergoni, 1970; A. Packard, unpublished). I know of no other animal groups in which the brain grows so extensively.  In terms of cell numbers the overall increase is rather less: a thousand-fold (2 x 105 in young octopus at hatching to 2 x 108 in tlie full-grown adult (Giuditta, Lihonati, Packard & Prozzo, 1971)). A forty-fold part of this cell accumulation takes place after the octopus has settled from the plankton (Packard & Albergoni, 1970). Comparable brain-cell figures for fish are not known. About half of the brain tissue in octopus, and between two-thirds and four-fifths in decapods, is in the optic lobes (Mangold-Wirz, see also Bullock & Horridge, 1965, p.1442): a preponderance that reflects the great dependence of these animals on vision (Fig. 2).

Fig. 2. Eye/brain dimensions. Weights (in grams) of the two eyes and optic lobes of the brain of the octopus (Octopus vulgaris) and cuttlefish (Sepia officinalis). Approtimate body weights alongside. Note the larger size of the cuttlefish eye and brain. (Original, from unpubished data)

In fish, the optic tecta and cerebellum, which can be thought of as the functional equivalent of the optic lobes, occupy approximately one-half of total brain volume (Geiger, 1956; Bath, 1965).  They are relatively larger in nectonic than in benthic species."

reference from A. Packard, Cephalopods and Fish - the limts of Convergence - pp.266-7  (Biological Reviews, vol.47,  1972, pp.241-307)

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content by M.Alan Kazlev,
page first uploaded 8 December 1999, last modified 19 October 2003