Thyasirid Clams are known from across the world’s oceans from the
intertidal zone to the ocean deeps. Many species are associated with cold seeps
and hot vents where food chains are based upon chemotrophic Bacteria and
Achaeans (micro-organisms that generate energy by processing chemicals in the
water or sediment without photosynthesis), and are probably themselves
symbiotic hosts to such chemotrophs.
In a paper published in the journal ZooKeys on 10 December 2014, PaulValentich-Scott of the Santa Barbara Museum of Natural History and CharlesPowell, Thomas Lorenson and Brian Edwards of the United States Geological Survey describe a new species of Thyasirid Clam from the Canning Seafloor Mound
in the Beaufort Sea off the north coast of Alaska.
The new species is named Wallerconcha sarae,
where ‘Wallerconcha’ honours Thomas
Waller of the Smithsonian Institution, for his work on living and fossil
Bivalves (‘Wallerconcha’ literally
translates as ‘Waller’s shell’, though this is not explained in the text) and ‘sarae’ honours Sara Powell, the daughter
of Charles Powell.
Wallerconcha sarae, length = 23.9 mm, height = 21.3 mm, width = 16.7 mm. (A) Exterior
of right valve. (B) Exterior of left valve. (C) Dorsal view of both valves. (D)
Close up of periostracum of right valve. (E) Interior of left valve. (F) Interior
of right valve. (G) Close up of hinge of left valve (H) Close up of hinge of
right valve. Valentich-Scott et al. (2014).
The species is described from five shells, plus some additional
fragmentary material, collected in two sediment cores from the Canning Seafloor
Mound, ranging from 12.8 mm to 23.9 mm in length. No soft tissue was preserved
with the shells, so their biology is unclear, but Canning Seafloor Mound is
considered to be a cold seep environment (i.e. an environment in which
hydrocarbons are seeping from buried sediments into the water column, providing
a distinct chemical environment favourable to chemotrophic Bacteria and
Achaeans) and the living Wallerconcha sarae
is likely to have either hosted collonies of such micro-organisms symbiotically
or have fed on free living ones.
The location of the Canning Seafloor Mound off the
coast of northern Alaska. Valentich-Scott et
al. (2014).
The shells were collected from between 2 cm and 4.65 m below the
surface. Valentich-Scott et al. estimate
that the sedimentation rate at the Canning Seafloor Mound to be about 50 cm per
thousand years, which would make the shells less than 10 300 years old, with
the youngest being quite recent. However this does not take into account the
sediment compaction rate. The oldest shell was found at a level that also
contained the plankticforaminiferan Neogloboquadrina pachyderma,
which is considered to have been extinct for 1.8 million years, suggesting that
this specimen is at least that old, while a partial shell of the Gastropod Neptunea was found at a depth of 2.31 m,
also associated with a shell of Wallerconcha sarae.
This Snail is known from the earliest Miocene to the Holocene in the North
Pacific, and from the late Pliocene to the Holocene of the Arctic Ocean and
North Atlantic, being thought to have originated in the Pacific and entered thr
other areas after the opening of the Bering Strait in the latest Miocene or
early Pliocene, giving a maximum age to these sediments at around the
Miocene/Pliocene boundary.
Shaded seafloor bathymetry showing shape and
approximate dimension of the Canning Seafloor Mound. The core sites are shown
as red dots. Valentich-Scott et al. (2014).
See also…
Thyasiroid Clams are a group of Veneroid Bivalves found in deep
waters around the world. They are not well understood as a group, as most
species are known only from their shells, which allows for only a limited
understanding of their soft tissue anatomy and lifestyle.
Giant Clams of the genus Tridacna are large Bivalve Molluscs in
the Cockle Family (Cardiidae). They are extremely distinctive, both for
their large size and their bright colouration, which is caused by
symbiotic algae that live within the flesh of their mantles. Giant Clams...
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