Saturday 14 July 2012

Deep-sea Gastropods from Miocene Cold Seeps and Whale-falls in Japan.

Gastropod Molluscs of the genus Provanna have been found in a number of different deep-sea environments, including Hydrothermal Vents (areas where hot, chemical rich, waters emerge from submerged volcanic vents), Cold Seeps (areas where hydrocarbons escape into the sea from exposed deposits) and Whale- and Wood-falls (large organisms such as Whales or trees create nutrient-rich micro-environments when they sink into the generally nutrient-poor deep ocean). They feed primarily on filamentous bacteria that prosper at these sites, though some species are more general detritus feeders.

Provanna buccinoides at the Lau Basin Hydrothermal Vent  in the South Pacific. Kevin Zelnio/The Other 95%/Charles Fisher/Penn State.

The group have a limited fossil record, with Provanna fossils known from Cretaceous Cold Seeps in Japan, Miocene Cold Seeps in New Zealand and Eocene-Oligocene Cold Seeps and Wood-falls in Washington State.

In a forthcoming paper in the journal Acta Palaeontologica Polonica, Kazutaka Amano of the Department of Geoscience at Joetsu University of Education and Crispin Little of the School of Earth and Environment at the University of Leeds describe new Provanna fossils from a Miocene Cold Seep at Kuroiwa in central Honshu, and from two Miocene Whale-falls, one in Shosanbetsu in northwestern Hokkaido and the other in Rekifune in eastern Hokkaido.

Map of Japan showing the new Provanna sites. (1) The Shosanbetsu Whale-fall site. (2) The Rekifune Whale-fall site. (3) Kuroiwa Hydrocarbon Seep site. Amano & Little (2012).

The specimens from the Kuroiwa Hydrocarbon Seep site are described as a new species, Provanna hirokoae, named in honour of Kazutaka Amano's wife. These are medium-sized snail shells, slightly under 10 mm in length, with variable surface patterning.

Specimens of Provanna hirokoae from the Kuroiwa Hydrocarbon Seep site. Amano & Little (2012).

The specimens from the Shosanbetsu Whale-fall site are described as a second species, Provanna alexi, named in honour of Crispin Little's son. These are smaller (up to 6.5 mm), and less variable.

Specimens of Provanna alexi from the Shosanbetsu Whale-fall site. Amano & Little (2012).

Only two specimens were recovered from the Rekifune Whale-fall site, and these were not well preserved. As such there were described as members of the genus Provanna, but not assigned to a specific species.

Specimens of Provanna sp. from the Rekifune Whale-fall site. Amano & Little (2012).

See also Thirteen new species of interstitial Gastropods from New ZealandA new species of Scallop from Western AustraliaThe Snail that eats CrabsTwo new hydrothermal vent communities from the southern Central Indian Ridge.

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