Marine Copepods of the Genus Anthessius from the 
Northeastern Pacific Ocean 1 
Paul L. Illg 2 
Among the copepods associated with inverte- 
brates there is a remarkably homogeneous col- 
lection of species, predominantly associated with 
mollusks, comprising the genus Anthessius Della 
Valle 1880. The indications are strong that the 
mollusks will exclusively furnish the hosts of 
the members of the genus. Investigations of the 
invertebrate fauna of the Pacific Coast of the 
United States has resulted in the discovery of 
four species. One of these, Anthessius navanacis 
(Wilson, 1935), is known from California due 
to the fruitful ecological studies of Professor 
and Mrs. G. E. MacGinitie. From collections of 
the U. S. Steamer "Albatross,” we have from 
Hawaii Anthessius hawaiiensis (Wilson, 1921). 
In the description of new species in a genus so 
anatomically consistent, it was necessary to in- 
voke details not available in the original descrip- 
tions of these older species. Accordingly, they 
are redescribed below, with some emendations. 
For support of much of the research contribut- 
ing to this paper I am indebted to Fund 171, 
State of Washington. The illustrations for three 
species are based on pencil renderings by Mr. 
R. U. Gooding. Other drawings and the writing 
of the paper have been completed during the 
tenure of a John Simon Guggenheim Memorial 
Foundation Fellowship. I am indebted to many 
colleagues for assistance in connection with this 
report, and am most particularly obliged to Mr. 
John E. Fitch for his considerable efforts in col- 
lecting for me the material of the species named 
for him below. 
The genus Anthessius Della Valle dates from 
1880, with two species described as associates 
of Mediterranean mollusks. A still earlier species 
is now included in the genus. This is Boeckia 
arenicola Brady 1872^, 1872/?. As Boeckia is a 
preoccupied generic name, Brady subsequently 
1 Contribution No. 139 , Hawaii Marine Laboratory. 
2 Department of Zoology, University of Washing- 
ton, Seattle, Washington. Manuscript received May 
29 , 1959 . 
referred to this species as Lichomolgus arenicolus 
(1880: 46-47). It has been referred to in 
this combination by several authors, and also 
as Herrmannella arenicola, following T. Scott 
(1898). No host was known for this species until 
Bocquet and Stock (1958) demonstrated that 
A. arenicolus is an associate of Dosinia exoleta 
(L), and, further, clarified the systematic con- 
fusion of this species with their A. teissieri 1958 
in much of the published record. Such reinvesti- 
gations as that of Bocquet and Stock of many 
of the known species are needed to solve bio- 
nomic problems and to expand anatomical de- 
scriptions for provision of a sound basis for the 
resolution of the discrepancies found in the 
literature on the systematics of the genus. The 
work of these authors added to the revisionary 
summary of Monod and Dollfus ( 1932 ) and 
the review of Sewell (1949) provide the basis 
for the present treatment of the group. In the 
published record so far, the genus is still referred 
to the family Lichomolgidae, although the ap- 
propriateness of this attribution has already 
been questioned (Illg, 1949: 393). Myicolidae 
Yamaguti 1936 is available in Cyclopoida Poe- 
cilostoma among the families in the complex 
containing Clausidiidae and Fichomolgidae. I 
follow de Vos in Korringa and Lambert ( 1951: 
18-19) in assigning Lichomolgus spinosus Raf- 
faele e Monticelli 1885 not to Anthessius, but 
to the closely related genus, Pseudomyicola 
Yamaguti 1936. Pseudomolgus Sars 1916 is a 
synonym of Anthessius and the list of species 
so assigned must be transferred, as shown by 
Monod and Dollfus. The group of species now 
comprising Anthessius form a most coherent 
series of forms for which some morphological 
generalizations now can be made. Considerable 
emphasis has been laid by some authors on the 
importance of the condition of the segment of 
the first legs, relative to its alternative fusion 
with or separation from the cephalosome. Study 
of five species leads me to conclude that typically 
337 
