PSYCHE 
Vol. 57 September, 1950 No. 3 
NAJADICOLA INGENS (KOENIKE), 
A WATER-MITE PARASITIC IN FRESH-WATER CLAMS 
Arthur G. Humes and Hugo A. Jamnback 
Department of Biology, Boston University 
The distribution of Najadicola ingens (Koenike 1895) Piersig 
1897, a hydrachnid parasite of fresh-water clams in North America, 
is known only from a few scattered records. Relatively few speci- 
mens have been reported up to the present. Koenike (1895) de- 
scribed the species from specimens found in Anodonta fragilis 
Lamarck and Unio complanata (Solander ) 1 and sent to him by Dr. 
Tyrrell of Ottawa. The collection locality was given only as Canada. 
Wolcott (1899) collected this mite from Anodonta fragilis at “26” 
Lake, near Charlevoix, Michigan, and Intermediate Lake, Ellsworth, 
Michigan, from Unio gibbosus Barnes, U. ligamentinus Lamarck, 
and Anodonta footiana Lea at Grand Rapids, Michigan, and from 
U . luteolus Lamarck at Long Lake, Kalamazoo, Michigan. He ex- 
amined 3500 clams representing 60 species from Michigan, Wiscon- 
sin, Nebraska, New York, Illinois, Iowa, and Pennsylvania, but 
found not more than 16 specimens, all from the Michigan localities 
just mentioned. Wolcott (1918) stated that the species is generally 
distributed, but did not give additional distribution records. Marshall 
(1929) reported 16 adults and a few nymphs in two specimens of 
Anodonta in a small lake on Bruce peninsula, near Georgian Bay, 
Ontario. Kelly (1899) examined 1614 clams representing 44 species 
from Illinois, Iowa, and Pennsylvania, but reported no N. ingens, 
although he found several species of Ataoc (now Unionicola ). In 
view of the abundance indicated below of N. ingens in New Eng- 
lr rhe name Unio is now properly applied to certain European clams, the 
North American species formerly included having been placed in other 
genera. 
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