THOMPSON, J.T.: The ontogeny of squid mantle structure and function

The mantle of cephalopod molluscs is composed of a complicated arrangement of several different muscle and connective tissue components. Much is known about mantle structure and function in adult squid. However, significant alterations in mantle organization occur during ontogeny that may entail significant changes in mantle function. To understand the functional implications of ontogenetic changes in mantle morphology, I studied mantle connective tissue arrangement and mantle kinematics in Oval Squid, Sepioteuthis lessoniana. In the mantle, the fiber angle of collagen fibers in intramuscular fiber system (IM) 1 and IM-2 was lowest in hatchling squid and increased exponentially during growth in squid up to 15mm dorsal mantle length (DML). In squid larger than 15mm DML, IM-1 and IM-2 fiber angles did not change significantly. A simple model of mantle function based on IM collagen fiber arrangement predicts that the amplitude of mantle movement during jet locomotion will be highest in hatchling squid and will decline with growth. Video records of escape jet behavior in tethered S. lessoniana supported the ontogenetic change in mantle kinematics predicted by the model. During the escape jet, mantle hyperinflation and mantle contraction were greatest in newly hatched animals and decreased exponentially during growth in squid up to 15mm DML. Mantle hyperinflation and contraction did not change significantly in squid larger than 15mm DML.h