ANDERSON, M.J.; SMITH, S.D.; MILLER, J.T.; WILLIAMS, E.E.: The lipid composition of hypodermal microvilli from the carapace of the blue crab (Callinectes sapidus) changes during the molt cycle.

Growth in crustaceans involves the formation of a new, pliant cuticle beneath the existing one. The old cuticle is shed by the animal (ecdysis) and the new cuticle rapidly expands in volume and hardens by calcification. Calcification is complete within a few hours and is carried out in large part by abundant microvilli that arise from the cells of the outer epithelium of the hypodermis and extend deep into the cuticle within pore canals. Some of the biochemical transformations that occur in the cuticle during this critical period of expansion and hardening have been examined, but there is little information on the character of the lipid microenvironment of the microvillar membrane extensions during the molt cycle. We excised sections of the of the lateral carapace of adult blue crabs at 0, 2, 4, 6, 12, and 24 hours after ecdysis. The hypodermis was removed by swabbing, leaving the deeply embedded microvilli. The sections were then analyzed for lipid composition. Total tissue lipid content rose three-fold (10 to 30 mg/g tissue) between 0 and 24 hours post-ecdysis, encompassing a doubling of the phospholipids and a 4-fold increase in the neutral lipids. Cuticular cholesterol content peaked sharply at 6 h. The fatty acid distribution of phosphatidylcholine, which was highly enriched in palmitic acid, exhibited little change during the first 24 h after ecdysis, but the proportions of saturated fatty acids 22 and 24 carbons in length (docosanoic and tetracosanoic acids) in phosphatidylethanolamine rose to a maximum between 6 and 12 hours. These changes in the lipid microenvironment, and their timing, might have important influence on the volume expansion and calcification processes in the crustacean cuticle.