Physiology of Finfish and Shellfish (2+1)

2.2.23. Circulatory system of cephalopods - Heart

The Nautilus sp. has a heart with four auricles, while the decapoda and octopoda, has a heart with only two auricles. This difference is connected with the difference in the number of the ctenidia, four in Nautilus (tetrabranchia), two in the Decapoda and Octopoda (Dibranchia). In Nautilur, the heart is an almost square sac drawn out to two points on each side; the four auricles which open into the four points of the ventricles are long tubes, more like widened branchial veins than auricles. The stronghly muscular ventricle of the Dibranchia is almost always elongated into a tube.

In the Octopoda it lies transversely, the two auricles being in the same plaen with the ventricle. In the Ocgopsidoe, the ventricle lies along the longitudinal axis of the body. (i.e.) it is elongated dorsoventrally and the auricles are at right angles to it. The heart of the Myopsidoe occupies a position halfway between those just mentioned. The heart here described is the arterial heart, which corresponds with the heart of the other Mollusca. It is called arterial, to distinguish from the venous hearts, which was been described below.