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Among
endemic molluscs, the plurocerid gastropod Semisulcospira (Biwamelania)
group composes of 14 endemic species, and is solely considered
to be a "species flock", radiatively differentiated
taxon in the lake. The Biwamelania group is widely distributed
in the littoral areas; some species such as S. (B.) niponica
and morii are restricted to the rocky and/or gravel bottoms,
others like reticulata and mutigranosa to the sandy and/or muddy
bottoms, and others like habei and decipiens are widely distributed
in various kinds of bottoms. Only one recent species, S. (B.)
habei, is found in the fossils of the Paleo Biwa Formation Group
(Matsuoka, 1987), suggesting that habei like ancestor might
have evolved into the Biwamelania group. |
Semisulcospira in Lake Biwa