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Transactions of the Wisconsin Academy of Sciences, Arts and Letters
volume XXIII (1927)

Harring, H. K.; Myers, F. J.
The rotifer fauna of Wisconsin. IV. The Dicranophorinae,   pp. [667]-Plate 49 ff. PDF (41.5 MB)

Page 674

674 Wisconsin Academy of Sciences, Arts, and Letters.
one week among the hard water lakes and ponds around
Madison, Wisconsin; the same number was gathered in one
hour from a small, soft water lake at Eagle River, in north.
ern Wisconsin.
  The pH range of individual species appears to be as a
rule quite narrow, from 2 to 3 units pH; a few are able to
thrive through a greater range, but, as far as may be
judged from field observations, they are not numerous.
Perhaps the most striking fact observed is the total disap-
pearance of the genus Brachionus in acid waters, with the
single exception of B. polyacanthus. It is now quite evi-
dent why no Brachionids were found in Johansen's and
Jessup's collections in Alaska; the tundras are covered with
sphagnum growing knee-high and decaying rapidly, with
continuous accumulation of humic acid, leaching into the
shallow pools and ponds. Two Euchlanids are especially
interesting in this connection; E. triqutetra is ubiquitous in
alkaline waters, but not in acid, while E. pellucida is just
as abundant in acid water, but has never been found in
alkaline. The explanation of the rarity of certain rotifers
is now fairly simple: acid waters are not common where
rotifers have hitherto been studied most intensely. Thus,
Tetrasiphon hydrocora ( - Copeus spicatus) is usually ac-
counted rare; as a matter of fact it is common in acid water
regions. Brachionus polyacanthus was long supposed to be
non-extant; it is simply an acid water form. The same is
true of Proales doliaris, Notommata saccigera, Pleurotro-
cha robusta, Cephalodella globata, C. eva, Lecane brachy-
dactyla and L. ligona, not to mention a host of recently de-
scribed species; all are acid water animals, and it would
be useless to search for them in alkaline ponds. It will now
be fairly evident that ,the large number of new rotifers we
have found is not due to any superior skill or esoteric in-
formation, but solely to the fact that we have been fortu-
nate enough to have had access to numerous bodies of water
with different degrees of acidity.
   The years given to the gathering of evidence that might
 establish a correlation between rotifer distribution and
 hydrogen ion concentration have gradually brought forth
 a considerable body of literature, bearing more or less di-
 rectly on our subject. A few of the most important papers
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