668 



Fishery Bulletin 9I|4). 1993 



Embryonic Stage II (ES II): Similar to stage I but 

 a whitish mass of cells visible on yolk surface. This 

 mass is associated with a slight depression in the yolk 

 where the perivitelline space is deeper. 



Embryonic Stage III (ES III): A whitish embryo 

 without pigmentation clearly visible, occupying approxi- 

 mately 20% of egg volume. Eye spots clearly outlined. 

 A dorsal organ is present at opposite of embryo (cf. 

 ectodermal thickening of other malacostracan and 

 peracaridan embryos; Anderson, 1982). Abdomen is seg- 

 mented (5 somites+telson). Telson with 5-7 setae on 

 each of the two lobes. Antennulae and antennae have 

 setae-like projections. Three pairs of appendages are 

 formed posterior to the antennae: mandible, maxillula, 

 and maxilla. 



Embryonic Stage IV (ES IV): Egg ellipsoidal; em- 

 bryo occupies up to 50% of egg volume. Eye spots with 

 ocular pigments. Up to 200 red chromatophores present 

 on carapace. Dorsal organ no longer found. 



Embryonic Stage V (ES V): Egg ellipsoidal, pale 

 brown to pale orange. Fully developed zoea clearly vis- 

 ible. Embryo occupying from 50% to almost all of egg 

 volume. Yolk masses reduced and restricted to two dor- 

 sal areas in the anterior third of the cephalothorax. 

 All post-mandibular cephalothoracic appendages are 

 differentiated into 3 pairs of maxillipeds and 5 pairs 

 of pereopods, the last one reduced. Telson with 9 setae 

 on each lobe. Heart beat evident. 



Duration of embryogenesis and molt stages 



Females held in the laboratory were divided into two 

 groups on the basis of embryonic development. One 

 group of females had eggs in ES II from April 1990 up 

 to September 1990 through February 1991, when ES 

 III appeared. ES III did not last longer than two months 

 (in each egg mass) and in May 1991 all eggs were in 

 stage IV. Therefore, these eggs spent autumn and win- 

 ter in stage II, which suggests 

 an arrest in embryonic develop- 

 ment or diapause. The second 

 group of females had clutches 

 with eggs in ES IV in April 1990, 

 which hatched into larvae in Oc- 

 tober 1990. Post-ovigerous fe- 

 males molted in November 1990, 

 and then extruded and attached 

 eggs in the absence of males. 

 These eggs were unfertile since 

 females have no receptacle to 

 store male gametes (cf. sper- 

 mathecae in majids). The unfer- 

 tilized eggs were lost within the 

 next 20 days. 



Females collected from the Beagle Channel at any 

 time during the year had egg masses with eggs either 

 in early (I or II) or late (III, IV, or V) stages of develop- 

 ment (Table 1; Fig. 4A). ES I and ES II were generally 

 >40% in frequency during the two sampled years. ES 

 III never exceeded 5% in frequency and was observed 

 in February and August 1989, and in April, July, 

 and October 1990. These findings suggest that dia- 

 pause ends between early winter and late summer, 

 as observed in the laboratory. ES IV and ES V oc- 

 curred mainly from late autumn to early spring. Post- 

 ovigerous females appeared from late autumn to early 

 spring. 



Samples of P. granulosa taken from the study area 

 at any given time comprised females in at least two 

 different molt stages: either EIM or AIM occurred with 

 MIM (Table 1, Fig. 4B). PRM females occurred in Oc- 

 tober and POM females were found in October and 

 November 1989. 



Asynchronous embryonic development 



A portion of the females (21%; n=100) from the Becasses 

 Islands, and some from the area near Ushuaia (2%; 

 ft =395) carried clutches with eggs at different stages 

 of development: ES II and ES IV or V were found in 

 the same egg mass. This was observed around the 

 Becasses Islands in August 1990, where 7 females car- 

 ried eggs in ES II (at least 50% frequency in each 

 clutch) and in ES IV In October 1990, 12 females had 

 eggs in ES II (at least 50% frequency) and ES V. Two 

 other clutches had eggs in ES II and ES IV. The more 

 advanced eggs would probably hatch earlier than those 

 that were less developed. We could not determine 

 when hatching occurred because commercial fishing 

 around the Becasses Islands was suspended in Octo- 

 ber 1990 and the females were not held for further 

 observation. 



Table 1 



Embryonic development and shell condition of female Paralalias granulosa on 20 May 

 1990 in two localities, 10 km apart. ES=embryonic stages. Postovigerous females have 

 empty egg cases and funiculi attached to the pleopodal setae. MIM=median intermolt; 

 AIM=advanced intermolt. Frequencies for both embryonic development and shell-condi- 

 tion are significantly different between the two localities (G-test for homogeneity on 

 embryonic development = 12.66; P<0.005; G-test for homogeneity on shell condition = 

 23.45; P<0.005). 



Embryonic development 



Shell condition 



I .ocation 



ES I, II, 



and III 



ESIV 

 andV 



Postovig. 

 females 



MIM 



AIM 



Golondrina 

 Bridges Is. 



60 



44 



31 

 51 



64 

 31 



35 

 69 



587 

 84 



