At hydrothermal vents emitting fluids over 310°C around the living beds. Endemic to vents. The shell surfaces are covered with numerous filamentous bacteria. Periostracum color changes according to growth stages. Development not known but most probably with planktonic larval phase.

Izu Ogasawara Arc: Suiyo Seamount and Mokuyo Seamount.

Shell large, rather thin but solid, inflated, elliptical, more or less compressed. Umbones subterminal, less than one-eighth anterior of the shell length. Ligament weak. Extremely thick and large ctenidia with long demibranchs. No extreme mantle fusion, valvular siphonal membrane short. Anterior adductor muscle scar located below the umbo. Anterior part of the posterior byssus retractor muscle scar under posterior end of ligament, at about four-fifths of ligament length.

Shell length up to 124 mm.

Paratype for Bathymodiolus septemdierum Hashimoto & Okutani, 1994
Catalog Number: USNM 880289
Collection: Smithsonian Institution, National Museum of Natural History, Department of Invertebrate Zoology
Preparation: Alcohol (Ethanol)
Year Collected: 1992
Locality: Suiyo Seamount, Hydrothermal Vent Site, Japan, North Pacific Ocean
Depth (m): 1256 to 1256
Vessel: Shinkai 2000 DSR/V

Paratype for Bathymodiolus septemdierum Hashimoto & Okutani, 1994
Catalog Number: USNM 880290
Collection: Smithsonian Institution, National Museum of Natural History, Department of Invertebrate Zoology
Preparation: Alcohol (Ethanol)
Year Collected: 1992
Locality: Suiyo Seamount, Hydrothermal Vent Site, Japan, North Pacific Ocean
Depth (m): 1256 to 1256
Vessel: Shinkai 2000 DSR/V

Depth range based on 194 specimens in 1 taxon.
Water temperature and chemistry ranges based on 194 samples.

Environmental ranges
  Depth range (m): 1223 - 3600
  Temperature range (°C): 1.629 - 3.139
  Nitrate (umol/L): 38.302 - 42.519
  Salinity (PPS): 34.438 - 34.675
  Oxygen (ml/l): 1.376 - 3.369
  Phosphate (umol/l): 2.626 - 3.033
  Silicate (umol/l): 132.569 - 148.729

Graphical representation

Depth range (m): 1223 - 3600

Temperature range (°C): 1.629 - 3.139

Nitrate (umol/L): 38.302 - 42.519

Salinity (PPS): 34.438 - 34.675

Oxygen (ml/l): 1.376 - 3.369

Phosphate (umol/l): 2.626 - 3.033

Silicate (umol/l): 132.569 - 148.729
 
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