FISHERY BULLETIN: VOL. 71, NO. 4 



that permits i)assage of the sperm into the 

 female's seminal receptacles (Wolf, 1905; Neu- 

 baur. 1913; Heberer, 1932; Fahrenbach, 1962). 



Integumental organ systems are used widely 

 in arthropod systematics. Indeed, in some 

 groups, as for example, mosquitoes, dependence 

 upon chaetotaxy is essential. A unique and 

 particularly interesting application devised to 

 permit identification of the fossilized remains 

 of chydorid cladocerans in extinct lake sedi- 

 ments utilizes the number, size, and arrange- 

 ment of integumental pores (Frey, 1959, 1962). 



Despite repeated mention of integumental 

 organs in the early copepod literature, attempts 

 to apply them to study of marine species are 

 rare. Notable exceptions must include With's 

 (1915) detailed accounts of the sensilla sur- 

 rounding the oral region for a number of species 

 collected in North Atlantic samples. Sewell 

 showed considerable interest in the general 

 distribution of body integumental organs in 

 planktonic copepods. His observations made on 

 a broad variety of species are presented in 

 scattered notes, remarks, and illustrations 

 within the context of his faunal studies on 

 Indian Ocean calanoids (1929, 1932, 1947). 

 Unfortunately, the diminutiveness of these 

 organs, Sewell's omission of methods for study, 

 and a critical estimate of their reliability con- 

 tributed to their neglect by subsequent workers. 

 Two studies on bioluminescence in planktonic 

 copepods (David and Conover, 1961; Clarke et 

 al., 1962) call attention to the potential value of 

 luminescing integumental glands for identify- 

 ing the species of living specimens. 



Conventional taxonomic systems organizing 

 diversity among calanoid copepods are strongly 

 dependent upon sexually modified structures of 

 the adult (copepodid stage VI) sometimes 

 assisted by nonsexual morphological or meristic 

 features in the adult condition, as for example, 

 spination and setation of appendages, seg- 

 mentation of appendages, and segmentation of 

 body tagmata. These sources of diagnostic in- 

 formation serve all hierarchial levels, species to 

 family. Due to the nature of calanoid ontogeny, 

 all of these structures assume their definitive 

 state only in sexually mature adults. Thus, 

 juveniles lie outside of existing systems, males 

 and females are only rarely served by the same 



system, and genera that are relatively undistin- 

 guished in sexually modified structures tend to 

 be "taxonomically difficult." 



The primary purpose of this paper is to 

 demonstrate the potential significance of sen- 

 silla and the pores of integumental glands on the 

 body tagmata to the systematics and phylogeny 

 of calanoid copepods. From a survey of these 

 organs in the genus Eucahuius, their numbers 

 and arrangements provide an objective basis for 

 grouping related s])ecies, for distinguishing 

 between sibling species, for relating adults of 

 either sex to their respective species despite 

 the elimination of other common characters 

 by sexual dimorphism, for aiding in the specific 

 identification of late immature copepods, and for 

 the determination of regionalized cohorts that 

 apparently lack unrestricted gene flow with 

 morphologically similar cohorts in other 

 regions. 



REMARKS ON THE GENUS 

 EUCALANUS UANA, 1853 



Eucalanus is a universally familiar marine 

 genus of eucalanid copepods. It contains pri- 

 mary consumers that form a conspicuous part 

 of the epiplanktonic and uper mesoplankton in 

 low to middle latitudes; some of the species are 

 primarily oceanic, others are neritic. Within its 

 habitat many of the species tend to be among 

 the most abundant and largest (adult total 

 length ranges from about 3 to 7 mm) of the 

 regional copepod fauna. Since the inception of 

 the genus for E. atteniiatus (Dana, 1853), about 

 25 nominal species have been proposed. Contri- 

 butions by Giesbrecht (1892), Johnson (1938), 

 and Vervoort (1946, 1963) provide the frame- 

 work for the genus and its taxa. The current 

 world literature indicates 12 nominal species 

 in active use. Two are represented by two sub- 

 species each, yielding a total of 14 widely 

 accepted taxa. 



Though Eiicalauux is a morphologically dis- 

 tinctive genus and its species are widespread 

 and relatively abundant, frequent questions and 

 confusion about the validity and rank of its 

 nominal s})ecies and subspecies tarnish its 

 literature. Difficulties with the identification 



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