NO. 3574 COPEPOD CRUSTACEANS — LEWIS 131 



Remarks. — Callgus quadratus, C. productus, and C. bonito are 

 difficult to separate not only because of the similarity in their mor- 

 phology but also because they are found on the same species of hosts 

 and not too infrequently they may be on the same host specimen. 

 Although this leads to some speculation on the relationships of the 

 three, there is some e\4dence to support the belief that they are 

 distinct species. This evidence, or part of it, can be used to separate 

 the species without going through a complete morphological analysis. 

 Assuming that the general body shape and nmnber of segments in 

 the thoracic legs agrees with the figures (i.e., that the specimens 

 belong to this species complex), Caligus productus can be separated 

 by the absence of the 3 plimiose setae normally present on the inner 

 margin of the second segment of the exopodite of the first thoracic 

 leg. Both Caligus qiiadratus and C. bonito possess these 3 setae, 

 but C. bonito possesses a series of distinct denticulations on the outer 

 margin of the first and second segments of the endopodite of the 

 second thoracic leg. Caligus quadratus, on the other hand, 

 possesses a patch of stiff pliunosities in the same region. The dif- 

 ference between stiff plumosities and denticulations is not great 

 but it is a distinct difference and sufficiently diagnostic to be used 

 as a key characteristic. 



Caligus asymmetricus, Kabata 1965b 



Figures 49-51 



Caligus thynni Pillai, 1963, p. 89, fig. 14. 



Caligus asymmetricus Kabata, 1965b, p. 110, figs. IB, D, E. 



Caligus asymmetricus Pillai. — Kabata, 1965b, pp. 109, 110. 



Distribution and host.^ — ^Trivandrimi, South India, Euthynnus 

 affinis {in Pillai, 1963) ; Queensland, Austraha, Euthynnus alleteratus 

 {in Kabata, 1956b). 



Remarks. — Dana (1853, p. 1353) described the caligid Caligus 

 thymni "from the external surface of a Bonito {Thymnus pelamys) 

 . . . ." Presiunably the species was named after the host although 

 the spelling of the generic part of the host name {Thymnus) has, to 

 my knowledge, never been used in the taxonomy of the tunas, the 

 name being Thynnus. The name Caligus thymni again appears 

 (p. 219) in a handwritten "Catalogue of Crustacea of the U.S. Expl. 

 Exped. during 1838-'42 . . . collected and described by James D. 

 Dana. Geologist and Zoologist Exp.," dated 1856 by Dana and 

 located in the U.S. National Museum. Yamaguti (1963, p. 61) 

 uses "C. thymni [misprint for thynni] Dana, 1853 . . ." in his account. 

 It is highly probable that thymni was not a misprint but a lapsus 

 by Dana, based on his erroneous spelling, Thymnus, of the host 



