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PACIFIC SCIENCE, Vol. XXII, October 1968 
The two populations thus differ in the very 
presence of a breeding season in the population 
at Pescadero Point. 
Constant breeding can be considered as an 
extremely prolonged breeding season. The aver- 
age ocean temperature at Point Fermin is several 
degrees higher than at Pescadero Point, and a 
lengthening of the breeding season in the south- 
ern portion of the range of temperate zone 
invertebrates is known in other groups, e.g., the 
sea urchin Arbacia punctulata (Harvey, 1956). 
Additional examples are discussed by Giese 
(1959) and Clark (1965). 
Other differences have been noted between 
the two populations. The heaviest female re- 
ported by Reish weighed approximately 50 mg, 
and smaller specimens seemed to be the rule, 
at least in his laboratory-raised animals. The 
largest female found at Pescadero Point weighed 
more than 1 gram, and mature females usually 
weighed in excess of 500 mg; the animals in the 
Pescadero Point population are thus an order of 
magnitude heavier than those in the Point Fer- 
min population. 
A further difference between the populations 
involves the site of origin of the oocytes. Reish 
(1954£) found them to originate from a solid 
tissue within the parapodia, from which clumps 
of oocytes are released upon achieving a diameter 
of up to 2 Op. Such a parapodial tissue has never 
been observed in N. grubei from Monterey 
County, although oogonial proliferation has 
been demonstrated autoradiographically in small 
clumps of oogonia floating free in the coelom 
(Schroeder, 1966). Mature oocytes from ani- 
mals in the Point Fermin population were found 
to range in diameter from l62p to 380p. At 
Pescadero the size range was much narrower, 
190p to 21 Op. Oocytes within a given mature 
female are very uniform in size. 
Reish (1954£) raised specimens from the 
Point Fermin population to maturity in his lab- 
oratory and found that while they usually meta- 
morphosed after 28 to 29 weeks, exceptional 
specimens metamorphosed at as early as 14 
weeks of age. This variability recalls that ob- 
served by Hauenschild (1966) in Platy nereis 
dumerilii. Although the life span of a worm 
from the Pescadero Point population is not 
known, it must be close to a year at a minimum, 
and is more likely to be 2 years. The period of 
oogenesis alone lasts 7 to 8 months, and much 
smaller animals than those in which gametes are 
found may be collected simultaneously. The de- 
velopment time at Pescadero Point is therefore 
2 to 4 times as long as the laboratory develop- 
ment time for specimens from the Point Fermin 
population. 
Whether these differences are simply expres- 
sions of latitudinal variation within a species, 
or whether they indicate that a deeper distinc- 
tion exists between these two populations can- 
not be determined from the available informa- 
tion. The morphological identity of the two 
forms has been graciously confirmed by Dr. 
Reish, who has clarified the taxonomic position 
of the species in conjunction with his work on 
its life history (Reish, 1954^). 
SUMMARY 
1. The major algal associates of Nereis grubei 
at Pescadero Point, Monterey County, Califor- 
nia, are Egregia menziesii and Gastroclonium 
coulteri. The Egregia holdfasts contain more an- 
imals during the fall and winter. 
2. At Pescadero Point, Nereis grubei breeds 
from February to June in approximately monthly 
swarms. 
3. Animals collected in December may be as- 
signed to a specific swarming group by deter- 
mining each animal’s average oocyte diameter. 
4. The average rate of oocyte growth between 
100p and 200p is 1.6-1.7p/day. This repre- 
sents more rapid growth than is shown by 
smaller oocytes. 
5. The central Californian population differs 
from that in southern California in its limited 
breeding season, in the average size of the com- 
ponent individuals, and in the internal site of 
oogenesis. 
ACKNOWLEDGMENTS 
The author warmly appreciates the assistance 
of Dr. Isabella Abbott in identifying the algae, 
of Mrs. Dana Pierce in preparing the figure, of 
Dr. Donald Reish in definitively identifying the 
worms, of Dr. Donald Abbott in critically re- 
viewing the manuscript, and especially of Dr. 
