Extracellular Lipid Droplets in<i>Idiosepius notoides</i>, the Southern Pygmy Squid

Abstract

Cephalopod metabolism typically involves carbohydrates and proteins, so that the lipid content of the mantle and all internal organs except the digestive gland is very low. Despite clear evidence of nonlipoid metabolic trends in cephalopods, we observed extracellular spheres, or droplets, in the cecum and digestive gland of newly collected juvenile, male, and female individuals of Idiosepius notoides, the southern pygmy squid. Prior to staining, the droplets were various shades of yellow and were often large enough to detect at 7 x magnification. The droplets were less dense than water, hydrophobic, and sudanophilic, staining positively with Sudan III, Sudan IV, and Sudan Black B. We conclude that these spheres are lipid and that they derive from the squid's normal field diet. When newly collected squid were starved in the laboratory, the droplets disappeared in 7-8 d and then reappeared in the cecum about 3 h after feeding.