Neanthes caudata — - Reish 
223 
GROWTH IN NEANTHES CAUDATA AND NEREIS GRUBEI 
Fig. 8. Growth in Neanthes caudata and Nereis grubei as measured by the number of segments per unit time. Data 
for Nereis grubei taken from Reish (1954: 16). 
segments were attained about 10 days before 
spawning. No sexual differences were noted 
with regard to the appearance or number of 
segments, and there was no indication that 
the males increase their number of segments 
between their first and second reproductive 
periods. 
So far as is known, there seem to be two 
types of growth curves in the nereids when 
the appearance of segments is used as the 
unit of measurement. Neanthes caudata pos- 
sesses a sigmoid growth curve with an inter- 
rupted plateau occurring at the onset of 
feeding. There is no initial prolonged phase 
after the appearance of the three larval seg- 
ments in N. caudata , as is typical for the 
majority of nereids. It is possible that N. 
lighti is characterized by an interrupted growth 
curve. A similar initial spurt as in N. caudata 
was found when the data from Smith (1950) 
was plotted. Development of N. lightiw&s not 
followed after birth by Smith. As summarized 
in Table 1, several nereids incubate their 
young, but either data were not included or 
development was not continued far enough 
to ascertain whether or not these species 
possess a growth curve similar to N. caudata. 
Sexual maturity was reached in 65 days 
(Table 2) with the female laying her eggs, 
and the male incubating them. The F 2 gen- 
eration reproduced 148 days later, and the 
F 3 generation reproduced 203 days later. Five 
generations have completed their life cycle in 
the laboratory within a period of one year. 
No gross morphological differences between 
the different matings or generations were 
