THE BIOLOGY O F WOOD-BORING TEREDINID MOLLUSCS
445
density influences the duration of adult life more than any other single
factor ” is significant.
The conversion of cellulose into assimilable sugars seems to be
accomplished by enzymes both from the style and the digestive diverticula. The role of the former is probably preparatory, acting on
large molecules and reducing the food into a soluble state, enabling
extracellular digestion of the non-nitrogenous food to take place in the
stomach and the caecum (appendix) especially the large wood fibres
which cannot be taken whole into the cells of the specialized region of
the digestive diverticula (Nair, 1955b, 1955c, 1956~) 1957b). It is
evident that the style splits the cellulose into the intermediary cellobiose
and probably passes it on for intracellular digestion in the diverticula
(Nair, 1956e). It is not known whether this disaccharide, cellobiose, can
be directly absorbed by the coiled typhlosole of the caecum. Thus the
cellulose splitting seems t o take place in steps in two different sites, one
extracellularly in the caecum and the other intracellularly in the
vacuoles of the digestive diverticula which has a cellobiase powerful
enough to complete digestion, thereby fully exploiting the nutrient
resources of the wood. Phagocytes playing an important role in the
digestive process are not, however, improbable, for Yonge (192(1,
1926a) has noticed phagocytes around the stomach, digestive diverticula
and midgut passing into the lumen of the gut ingesting particles of food
which they later carry back to the tissues and digest. Phagocytosis
does occur in the digestive diverticula of Mytilus, Ostrea (Vonk, 1924)
and Teredo (Potts, 1923). Greenfield (1959), who summarized previous
work, concluded that the evidence from experimental data strongly
suggests cellulolytic activity in shipworms and the utilization of the
end products of the process. It will also be worth while, as suggested by
Turner (1966), to “ investigate the presence of bacteria and fungi in the
wood itself and check on the possible reduction of the cellulose before
it is ingested by the shipworm.”
Despite this evidence strongly in favour of enzymic hydrolysis of
cellulose, Florkin and Lazet (1949) showed that in the classical case of
HeEix pomatia cellulase is produced by (symbiotic?) bacteria. Jeuniaux
(1950, 1954) investigated the origin of chitinase and found that bacteria
produce this enzyme and not the snails (Achatina fulica, Helix nsmoralis, H . aspera, Limax cinereoniger, etc.). Therefore, as Wee1 (1961)
has cautioned “ future investigations on species believed to produce
special enzymes themselves will be needed to show whether this claim
is correct or not.” It will also be interesting to find out the effect of
ageing on the production and utilization of enzymes in these specialized
bivalves.
445
density influences the duration of adult life more than any other single
factor ” is significant.
The conversion of cellulose into assimilable sugars seems to be
accomplished by enzymes both from the style and the digestive diverticula. The role of the former is probably preparatory, acting on
large molecules and reducing the food into a soluble state, enabling
extracellular digestion of the non-nitrogenous food to take place in the
stomach and the caecum (appendix) especially the large wood fibres
which cannot be taken whole into the cells of the specialized region of
the digestive diverticula (Nair, 1955b, 1955c, 1956~) 1957b). It is
evident that the style splits the cellulose into the intermediary cellobiose
and probably passes it on for intracellular digestion in the diverticula
(Nair, 1956e). It is not known whether this disaccharide, cellobiose, can
be directly absorbed by the coiled typhlosole of the caecum. Thus the
cellulose splitting seems t o take place in steps in two different sites, one
extracellularly in the caecum and the other intracellularly in the
vacuoles of the digestive diverticula which has a cellobiase powerful
enough to complete digestion, thereby fully exploiting the nutrient
resources of the wood. Phagocytes playing an important role in the
digestive process are not, however, improbable, for Yonge (192(1,
1926a) has noticed phagocytes around the stomach, digestive diverticula
and midgut passing into the lumen of the gut ingesting particles of food
which they later carry back to the tissues and digest. Phagocytosis
does occur in the digestive diverticula of Mytilus, Ostrea (Vonk, 1924)
and Teredo (Potts, 1923). Greenfield (1959), who summarized previous
work, concluded that the evidence from experimental data strongly
suggests cellulolytic activity in shipworms and the utilization of the
end products of the process. It will also be worth while, as suggested by
Turner (1966), to “ investigate the presence of bacteria and fungi in the
wood itself and check on the possible reduction of the cellulose before
it is ingested by the shipworm.”
Despite this evidence strongly in favour of enzymic hydrolysis of
cellulose, Florkin and Lazet (1949) showed that in the classical case of
HeEix pomatia cellulase is produced by (symbiotic?) bacteria. Jeuniaux
(1950, 1954) investigated the origin of chitinase and found that bacteria
produce this enzyme and not the snails (Achatina fulica, Helix nsmoralis, H . aspera, Limax cinereoniger, etc.). Therefore, as Wee1 (1961)
has cautioned “ future investigations on species believed to produce
special enzymes themselves will be needed to show whether this claim
is correct or not.” It will also be interesting to find out the effect of
ageing on the production and utilization of enzymes in these specialized
bivalves.