Physiology

• Decapoda is the largest crustacean order and contains diverse forms
• Comparatively few species have been studied for their nutrition
• General accounts of decapod feeding and digestion are based on a small range of species
• Live lobsters used in the study were of carapace length 80-90 mm and in the intermoult condition
• Lobsters were maintained in a closed-circuit sea-water aquarium at 10-15°C
• Lobsters were killed by inserting a red-hot dissecting needle through the exoskeleton
• The oesophagus is a short, thick-walled duct leading from the mouth to the cardiac portion of the stomach
• Connective tissue below the oesophageal epithelium is packed with tegumental glands that stain intensely for acid mucopolysaccharides
• The two-chambered stomach of Homarus has a similar gross morphology to Nephrops
• The hepatopancreas, or digestive gland, is a yellowish-green paired structure flanking the stomach and anterior midgut
• The hepatopancreas is comprised of three lobes and lined by different cell types: E-, R-, F-, and B-cells
• The midgut of Homarus is formed from simple columnar cells and accounts for a significant portion of the postgastric intestinal tract
• The hindgut extends from the posterior midgut to the anus and is lined with chitin
• Stored materials in Homarus include glycogen in R-cells, unsaturated lipids in R-cell vacuoles, and small lipid droplets in F-cell cytoplasm
• In Homarus, the mandibles function as a 'vice' to hold food rather than to chew or bite it
• Decapoda is the largest crustacean order and contains diverse forms
• Comparatively few species have attracted studies on their nutrition
• General accounts of decapod feeding and digestion are based on a small range of species
• Investigations have focused on specific regions of the alimentary tract rather than digestion as a whole
• Live lobsters used in the study were of carapace length 80-90 mm and in the intermoult condition
• Lobsters were maintained in a closed-circuit sea-water aquarium at 10-15°C
• Individuals were killed by inserting a red-hot dissecting needle through the exoskeleton
• The heart and mid- and hindgut were exposed for study
• Ultrastereoscopic studies on the oesophagus were conducted by coating fragments in gold/palladium alloy and viewing them on a Scanning Electron Microscope
• Fragments of fish are picked up by the second pereiopods and passed to the third maxillipeds for feeding
• The dactylo-, pro- and carpopodites are then moved down over the food mass, pressing it up against the ischiopodites
• The oesophagus is a short, thick-walled duct leading from the mouth to the cardiac portion of the stomach
• Connective tissue below the oesophageal epithelium is packed with tegumental glands that stain intensely for acid mucopolysaccharides
• The two-chambered stomach's gross morphology is similar to that of Nephrops
• The hepatopancreas, or digestive gland, is a yellowish-green paired structure flanking the stomach and anterior midgut
• The hepatopancreas is comprised of three lobes in each half of the organ
• Tubules in the hepatopancreas are lined by an epithelium with E-, R-, F-, and B-cells, along with basophilic connective tissue and blood sinuses
• 1. cells, 15-25 µm tall, are restricted to the terminal, blind-ending regions of each tubule
• 1. cells characteristically contain an ovoid nucleus, approximately 8 µm in maximum diameter, with a conspicuous acidophilic nucleolar inclusion
• Resorptive (R) cells are typically multivacuolate in appearance
• 1. cells have an Alcian Blue and PAS-positive brush border approximately 1 µm in thickness
• 1. cells are 45-60 µm tall and are the most abundant hepatopancreatic cell-type
• 1. cell nuclei are 6-8 µm in diameter and lie medioproximally within the cells
• Fibrillar (F) cells are principally confined to the distal half of each tubule
• 1. cells are recognizable as strongly basophilic, 25-50 µm tall and 9-15 µm wide