| All animals with complex behaviours and closed circulatory systems face similar biological challenges. Well-studied examples of solutions to these challenges come primarily from the vertebrates. However, coleoid cephalopods (Phylum Mollusca) also have complex behaviours and closed circulatory systems. They provide examples of solutions that, while functionally similar to the solutions of the vertebrates, are structurally different. I investigated the structure of coleoid strategies for powering venous return, responding to sudden stimuli and regulating male agonistic behaviour.; Studies into cardiovascular function in coleoids, and especially in cuttlefish, have been limited using traditional techniques. I used ultrasound to image the circulatory organs of the cuttlefish, Sepia officinalis, for the first time. All the large veins (anterior and lateral venae cavae and efferent branchial vessel) contracted in unanaesthetized, untethered, resting cuttlefish. The anterior vena cava and lateral venae cavae contracted peristaltically. I discovered a muscular valve which separated these two unsynchronized vessels and ensured blood flowed in only one direction between them. Contractions of the veins were not timed to mantle movements in a way that was consistent between cuttlefish. Therefore, venous return is likely to be powered by venous contraction in resting cuttlefish, and not by pressures produced inside the mantle cavity by ventilation.; Like other animals, coleoids need to respond to novel, potentially threatening, stimuli in their environment. When resting cuttlefish were presented with a sudden visual stimulus, ventilation and heart rates fell below resting levels. Drops in ventilation and heart rates were inversely proportional to resting rates. Cuttlefish also showed components of the Deimatic Display (including behavioural freezing) and hyperinflated their mantles during the response. The Deimatic Display is part of cuttlefish predator avoidance behaviour. Behavioural freezing (including decreased ventilation rate) may help cuttlefish to prepare for flight by increasing sensory acuity. Mantle hyperinflation helps to prepare cuttlefish for flight by filling the mantle with water prior to escape jetting. Decreased heart rate may be a product of the unusual arrangement of muscles and capillaries in the cuttlefish mantle.; Male squid actively compete for mates. Squid are group-living, and are therefore continuously surrounded by both conspecific males and females. (Abstract shortened by UMI.)... |
