MALACOLOGIA, 1998, 40(1-2): 63-112
A NEW GENUS AND FIVE NEW SPECIES OF MUSSELS (BIVALVIA, MYTILIDAE)
FROM DEEP-SEA SULFIDE/HYDROCARBON SEEPS IN THE GULF OF MEXICO
Richard G. Gustafson^*, Ruth D. Turner^, Richard A. Lutz\ & Robert C. Vrijenhoek^
ABSTRACT
Five new species of modioliform mussels in the family Mytilidae are described from material
collected at sulfide/hydrocarbon seeps in the Gulf of Mexico. New definitive taxa, placed in the
subfamily Bathymodiolinae, include the genus Tamu and the species Tamu fisheri from hydro-
carbon seeps on the Louisiana Continental Slope, Bathymodiolus heckerae from brine seeps at
the base of the West Florida Escarpment in the eastern Gulf of Mexico, and Bathymodiolus
brooksi from the West Florida Escarpment site and from hydrocarbon seeps at Alaminos Canyon
in the western Gulf of Mexico. An additional two new mussel species, which exhibit combinations
of morphological characters unlike any existing mytilid genus but for which molecular data are
equivocal, are provisionally placed in the genera Bathymodiolus and Idas, respectively. These
are: "Bathymodiolus" childressi from hydrocarbon seeps at Alaminos Canyon and the Louisiana
Continental Slope, and "Idas" macdonaldi (in the subfamily Modiolinae) from hydrocarbon seeps
on the Louisiana Continental Slope.
Key words: Mytilidae, deep-sea, sulfide seeps, hydrocarbon seeps, Bathymodiolinae.
INTRODUCTION
Modioliform mussels in the family Mytilidae
are conspicuous members of many deep-sea
hydrothermal vent and cold-water methane/
sulfide seep environments. A common feature
of these mussels is their dependence on sul-
fide-oxidizing or methanotrophic symbionts
(Fisher, 1990; Cavanaugh, 1992). The first
vent mussel described was Bathymodiolus
thermophilus Kenk & Wilson, 1985, which oc-
curs at hydrothermal vents on the Galápagos
Rift and the East Pacific Rise (EPR). Recently
described species are: B. platifrons Hashi-
moto & Okutani, 1994; B. japonicus Ha-
shimoto & Okutani, 1994; B. adulcidos Hashi-
moto & Okutani, 1994; and B. septemdierum
Hashimoto & Okutani, 1994, from vent and
cold seep sites around Japan; B. brevier
Cosel, Métivier & Hashimoto, 1994, and B.
elongatusCosel, Métivier & Hashimoto, 1994,
from vent sites in the south Pacific; and B.
puteoserpentis Cosel, Métivier & Hashimoto,
1994, from the Snake Pit site on the Mid-At-
lantic Ridge. In addition, the small mussel Idas
washingtonia (Bernard, 1978) occurs at hy-
drothermal vents on the Juan de Fuca Ridge
in the north-eastern Pacific (Juniper et al.,
1992) and Amygdalum politum (Verrill &
Smith, in Verrill, 1880), a small thin-shelled
mytilid, occurs near cold water hydrocarbon
seeps on the Louisiana Continental Slope
(Turner, 1985).
As yet undescribed modioliform mussels
were reported from hydrothermal vents or
cold-seeps in the Pacific Ocean at Guaymas
Basin (Turner, 1 985), Middle Valley (Juniper et
al., 1992), the Mariana Back-Arc Basin
(Hessler & Lonsdale, 1 991 ), and the Mid-Oki-
nawa Trough (Hashimoto et al., 1995); and in
the Atlantic Ocean at the South Barbados ac-
cretionary prism (Jollivet et al., 1990) and on
the Mid-Atlantic Ridge at 37°50'N ("Menez
Gwen" site), 37°17'N ("Lucky Strike" site),
29°N ("Broken Spur" site), and 1 4°45'N (Cosel
etal., 1997).
An allozyme survey by Craddock et al.
(1995) identified several additional modio-
liform taxa from sulfide/hydrocarbon seeps in
the Gulf of Mexico. A subsequent analysis of
these specimens for DNA sequences from a
region of the mitochondrial Cytochrome с Ox-
^ Institute of Marine and Coastal Sciences, P. O. Box 231 , Rutgers University New Brunswick, New Jersey 08903, USA
^Museum of Comparative Zoology, Harvard University, Cambridge, Massachusetts 02138, USA
'Present Address; National Oceanic and Atmospheric Administration, National Marine Fisheries Service, Northwest Fish-
eries Science Center, Conservation Biology Division, 2725 Montlake Blvd. E., Seattle, Washington 98112-2097
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