The gut is generally an almost straight tube supported by the mesenteries (vertical partitions within segments), and ends with the anus on the underside of the pygidium. However, in members of the tube-dwelling family Siboglinidae the gut is blocked by a swollen lining that houses symbiotic bacteria, which can make up 15% of the worms' total weight. The bacteria convert inorganic matter – such as hydrogen sulfide and carbon dioxide from hydrothermal vents, or methane from seeps – to organic matter that feeds themselves and their hosts, while the worms extend their palps into the gas flows to absorb the gases needed by the bacteria. COUNT 5
QSN1 What type of annelids are tube-dwelling? ANS1 Siboglinidae QSN2 What blocks the Siboglinidae's gut? ANS2 a swollen lining QSN3 How much of a Siboglinidae's weight is symbiotic bacteria? ANS3 15% QSN4 What gases come from hydrothermal vents? ANS4 hydrogen sulfide and carbon dioxide QSN5 What gases come from seeps? ANS5 methane