Observations on the feeding mechanism,structure of the gut,and digestive physiology of the european lobster Homarus gammarus (L.) (Decapoda: Nephropidae)

Investigations have been made on the feeding mechanism, structure of the gut, and digestive physiology of the European lobster Homarus gammarus (L.).Ciné-photography has shown that the mandibles do not possess a masticatory function, merely serving to grip food morsels during the tearing process effected by the pulling action of the third maxillipeds. The remaining maxillipeds, together with the maxillae, then direct food fragments to the mouth for ingestion.Ingestion is facilitated by mucoid secretions discharged from the oesophageal tegumental glands; the glands do not appear to produce any enzymes which directly contribute to the digestive processes.The hepatopancreas is the principal organ concerned with digestion. It possesses a complex tubular organization in which sequential cellular differentiation culminates in the discharge of enzymes from the B-cells for extracellular digestion in the cardiac stomach. The enzymes are synthesized within vacuoles contained in the B-cell precursors (F-cells) and are secreted in three bursts of activity at 0–15 min, 1–2 h, and 3.5–5 h after a meal. The initial secretory phase is holocrine. Extracellular digestion involves esterases, arylamidases, and lipases; endopeptidases have not been positively identified by histochemical means despite the fact that Homarus is a carnivore. There is an intracellular digestive phase, not previously described in decapod crustaceans, at the 7–9 h post-ingestive stage in the hepatopancreatic R-cells which is effected by arylamidases and lipases.Various phosphatase enzymes have been identified in the hepatopancreatic cells. Acid and alkaline phosphatases are apparently concerned with several stages in the digestive cycle, including enzyme synthesis and secretion, and the absorption of digestive products. Adenosine triphosphatase activity is primarily associated with granules located in the distal R-cell cytoplasm; the possible significance of these granules in the elimination of metabolic wastes is discussed. Acid phosphatases and esterases are present in the midgut epithelium. The possibility of a passive uptake of material from the midgut lumen is considered.Faecal material in the hindgut is bound by mucoid secretions derived from the tegumental glands of this alimentary region; the mucus may also assist in defaecation.A complete digestive cycle in Homarus occupies ≈ 12 h.Food reserves in the gut consist principally of fat deposits in the R-cells, but minute amounts of glycogen can also be detected.No evidence of calcium, copper or ferric iron deposition in any part of the alimentary tract was found.