A New Copepod of the Genus Calanus from the Northeastern 
Pacific with Notes on Calanus tenuicornis Dana 1 
Thomas E. Bowman 2 
While enumerating copepods from net 
hauls made in 1949 and succeeding years off 
the California coast in connection with the 
California Cooperative Oceanic Fisheries In- 
vestigation (CCOFI), it was observed that 
specimens with characters agreeing with those 
given in the literature for Calanus tenuicornis 
Dana were of two types. One form, limited to 
the southern portion of the area investigated, 
had a longer and narrower body and relatively 
longer appendages. The other, more stubby, 
form had a wider distribution, with maximum 
numbers to the north. The problem of whether 
these two forms are environmentally deter- 
mined or whether they differ genetically on 
the specific or subspecific level invited in- 
vestigation. The results of this study, pre- 
sented herein, have led to the conclusion that 
the more stubby form is Dana’s C. tenuicornis , 
and the elongate form is a new species. 
Calanus tenuicornis was first described by 
Dana (1853: 1069) from the Central North 
Pacific. His description was brief, dealing 
chiefly with the first antenna. He figured 
(1855, pi. 73, fig. 10 a, b) a dorsal view of the 
adult female with the first antennae attached 
and detail of the distal end of the first 
antenna. Giesbrecht (1892, pis. 6-8) provided 
several additional illustrations. Figures pub- 
1 Published by permission of the Secretary of the 
Smithsonian Institution. Manuscript received January 
28 , 1955 . 
2 United States National Museum, Washington, 
D. C. 
lished by most authors following Giesbrecht 
(van Breemen, 1908, fig. 8, a-d; Pesta, 1920, 
fig. A, 3; Rose, 1933, fig. 12; Farran and 
Verwoort, 1951, fig. 3, a, h) are taken from 
Giesbrecht’s illustrations. Esterly (1905, fig. 
3, a, b) and Brodsky (1950, fig. 24) provided 
additional original figures. Since the append- 
ages of C. tenuicornis are identical with those 
of the new species (Figs. 1,2) in all details of 
segmentation and armature, its has not been 
deemed necessary to illustrate them here. 
A complete synonomy for C. tenuicornis is 
given by Verwoort (1946: 22) and need not 
be repeated. Additional references to this spe- 
cies are those of Mori (1937: 16, pi. 3, figs. 
9, 10, pi. 4, figs. 1-3), Wilson (1942: 195; 
1950: 269) Brodsky (1950: 95-97, fig. 24), 
Farran and Verwoort (1951: 3, fig. 3a, 3h), 
Rose and Vaissiere (1952: 116), and Yamazi 
(1953: 198). 
C. tenuicornis may be distinguished easily 
from other previously known species of Cala- 
nus by the elongate first antennae and the 
reduced size of the outermost setae of the 
furcae. Elongate first antennae are also char- 
acteristic of C. gracilis Dana and C. robustior 
Giesbrecht, but both these species differ from 
C. tenuicornis in having a strong hooked spine 
on the anterior aspect of the second basis of 
the first swimming legs. Furthermore C. tenui- 
cornis is much smaller than the other species 
( tenuicornis , 1.5-2. 4 mm.; gracilis , 2. 3-3. 3 
mm.; robustior , 3. 0-3. 8 mm.). In both C. 
gracilis and C. robustior the long setae on the 
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