THE LARVAL DEVELOPMENT OF 

 PACIFIC EUPHAUSIA GIBBOIDES (EUPHAUSIACEA) 



Margaret D. Knight^ 



ABSTRACT 



The larval development of Euphausia gibboides is described and illustrated, including nauplius 

 stages I and II, metanauplius stage, calyptopis stages I-III, and furcilia stages I- VI; dominant and 

 variant forms, with respect to reduction in number of terminal telson spines, were found in furcilia 

 IV- VI. Identification of developmental stages was substantiated by the study of a series of juveniles 

 oiE. gibboides, the largest of which had characters of both the furcilia phase and the adult. Larvae 

 were studied in plankton samples from several areas within the range of the species in the Pacific 

 Ocean; variation in size of calyptopes in different areas is described. 



Euphausia gibboides Ortmann is a relatively 

 large euphausiid of the temperate and tropical 

 Pacific. It is closely related to E. sanzoi Torelli 

 and E. fallax Hansen and with them forms a 

 "Euphausia gibboides group" (Brinton 1962). In 

 the North Pacific, E. gibboides is found in the 

 transition zone between lat. 30° and 45°N and 

 extending southward to about lat. 20°N in the 

 east where it is considered a major species of the 

 California Current system; in the South Pacific 

 it occurs in the eastern equatorial zone. Eu- 

 phausia sanzoi has been found in the Red Sea and 

 western Indian Ocean, and E. fallax in the west- 

 ern tropical Pacific. The distributions of these 

 species are discussed by Brinton (1962, 1967a, 

 b, 1973), Brinton and Gopalakrishnan (1973), 

 Roger (1967), and Mauchline and Fisher (1969). 

 The distribution of the larvae of £. gibboides in 

 the California Current is shown by Brinton 

 (1967a, b, 1973). 



Hansen (1911) divided the species of the genus 

 Euphausia Dana into four groups with respect 

 to armature of carapace and abdomen; of these, 

 groups A and D were considered to be "well sepa- 

 rated" but groups B and C "somewhat badly de- 

 fined." Group C, the largest of the four, contains 

 12 of the 32 species now recognized in the genus: 

 E. mucronata, E. paragibba, E. pseudogibba, E. 

 hemigibba, E. gibba, E. lamilligera, E. distin- 

 guenda, E. sibogae, E. gibboides, E. fallax, E. 

 sanzoi, and E. vallentini (E. aluae and E. con- 

 suelae, both considered difficult to evaluate are 



'Scripps Institution of Oceanography, University of Cali- 

 fornia, San Diego, P.O. Box 109, La Jolla, CA 92037. 



Manuscript accepted March 1974. 



FISHERY BULLETIN: VOL. 73, NO. 1, 1975. 



not included) (Boden et al. 1955). An early fur- 

 cilia of E. hemigibba (Lebour 1949) and a late 

 furcilia of E. distinguenda (Hansen 1912) have 

 been identified, but a series of developmental 

 stages has been described for only one of the 

 group C species, E. vallentini (John 1936). In 

 his investigation of the adults and larvae of the 

 southern species of Euphausia, John has shown 

 the affinity of E. vallentini and certain species 

 of group B with which it may now be associated 

 (Mauchline and Fisher 1969). Studies of the lar- 

 vae of additional species should aid not only in 

 identification of planktonic forms but also in 

 definition of specific relationships within the 

 genus. 



The present paper provides descriptions of the 

 developmental stages of Euphausia gibboides; 

 it is part of a larger study whose purpose is to 

 identify and describe larvae of the three species 

 of the "Euphausia gibboides Group" and to com- 

 pare the larval morphology of these closely related 

 forms. 



METHODS AND MATERIALS 



Larvae ofE. gibboides were obtained from pre- 

 served plankton samples in the Marine Inverte- 

 brate Collections of the Scripps Institution of 

 Oceanography. They were sorted from net hauls, 

 taken with the standard CalCOFI (California 

 Cooperative Oceanic Fisheries Investigations) 

 1-m net (Ahlstrom 1954), which were known to 

 contain larvae and juveniles of the species. The 

 positions of these tows are given in Table 1; 

 station data for the samples are given by Snyder 



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