The statocysts of cranchiid squids (Cephalopoda)

The statocysts of Cranchiidae are unlike those of all other squids. They are very varied: at one extreme is Bathothauma with a very large sac unique in having no internal interruptions. Conversely Egea has more of these anticristae than any other cephalopod. They are arranged in patterns that are different from those of other squids and they are sometimes very long and thin. The anticristae are large and numerous in the cranchiids that are perhaps more rapid swimmers and more active in hunting their prey, for example Mesonychoteuthis, Megalocranchia, Egea or Taonius. However, in the moderately large cranchiids Teuthowenia and Galiteuthis the statocyst cavities are little interruped by anticristae. The conditions of the statocysts are found to correspond well with the cladistic analyses of relationship within the family performed by N.A. and R.S. Voss, except for those of Teuthowenia and Galiteuthis which stand apart, having relatively uninterrupted cavities. Other genera showing this condition are mostly small animals and form a group of presumably neotenous forms as suggested by N. Voss. It is discussed whether these may be the more primitive genera in the group. Possibly the Cranchiidae arose as neotenous buoyant squids with a peculiar mantle cavity and coelom and uninterrupted statocysts. Later genera exploited these characters and when they became more active swimmers they developed anticristae with an original pattern, allowing monitoring of more rapid turns.