KNIGHT; LARVAL DEVELOPMENT OF EUPHAUSIA EXIMIA 



teeth of the right mandible as the lacinia mobilis 

 (Weigmann-Haass 1977; Hessler^). In species of 

 Euphausia I have examined in detail (E. gib- 

 boides, E. sanzoi, E. fallax, E. pacifica), in 

 Nematoscelis difficilis (Gopalakrishnan 1973), 

 and Nyctiphanes couchii (Le Roux 1976), the 

 lacinia mobilis appeared only on the right mandi- 

 ble; it was found on the left mandible of fi. hanseni 

 by Weigmann-Haass ( 1977). Leg 1 is referred to as 

 maxilliped through the furcilia phase. 



Adults were sorted from a set of samples (Figure 

 1) for preliminary exploration of morphological 

 differences between populations ofE. eximia. The 

 animals were sexed, measured to the nearest mil- 

 limeter, and the armature of telson and inner pro- 

 cess of segment 2 of antennular peduncle were 

 inspected. 



Gravid females o( E. eximia, captured in night- 

 time plankton tows with aim net from 200 m to 

 the surface near Santa Catalina Island, were cul- 

 tured aboard ship using the methods described by 

 Lasker and Theilacker (1965). Larvae hatched 

 from eggs spawned by one of the females were held 

 through calyptopis I to confirm identification of 

 early larval stages. 



RESULTS 



Observations of Reared Animals 



Two gravid females spawned on the night of 

 capture; they were 25.7 and 26.6 mm total length 

 (TL) and shed 154 and 196 eggs. Their ovaries 

 were blue before spawning and the embryos of the 

 newly laid eggs were pale blue; the color faded 

 before hatch. Of 154 eggs allowed to develop, 90% 

 hatched and, at 17°-19° C room temperature, the 

 duration of early larval stages was approximately 

 as follows: 24 h for the egg; 24 h for nauplius I and 

 II together; 48 h for the metanauplius. The first 

 calyptopis appeared on the fourth day after spawn. 

 These stages encounter similar temperatures in 

 the surface waters off Baja California. 



The spent female molted 6 days after spawning 

 without shedding more eggs; a spermatophore was 

 not found on the preserved female or her exuvia. 

 Three other ovigerous females survived capture 

 and molted twice, with 4 days between molts, 

 without spav^ming; each shed a spermatophore 



with the exuvia during the first molt and the 

 ovaries remained blue. 



Description of Larval Stages 



Larval development in the California Current 

 population (northern form) of^ Euphausia eximia 

 included the following stages: nauplius I and II; 

 metanauplius; calyptopis phase, three stages; fur- 

 cilia phase, six stages. The stage which followed 

 furcilia VI usually (in 92% of 53 individuals) had 

 the adult number of spines on the telson (one ter- 

 minal and two pairs posterolateral) and is referred 

 to here as juvenile I. The observed furcilia stages 

 are listed in Table 1 along with the development of 

 pleopods, telson, and antenna. Measurements of 

 the calyptopis, furcilia, and juvenile stages are 

 given in Tables 2 and 3. 



Table l. — Development of pleopods, telson spines, and an- 

 tenna in furcilia I- VI and juvenile I in the northern and south- 

 em forms of Euphausia eximia; ' = pair nonsetose pleopods, " = 

 pair setose pleopods. 



Table 2. — Measurements (millimeters) of metanauplius and 

 calyptopis I-III in the northern form of Euphausia eximia. 



'Robert R. Hessler, Professor of Oceanography, Scripps In- 

 stitution of Oceanography, Univ. Calif., La Jolla, CA 92037, 

 pers. commun. July 1978. 



315 



