Reproduction in the Aggregating Sea Anemone, Ant ho pleura elegantissima 
Charles E. Ford, Jr , 1 
ABSTRACT: From a sample of 240 specimens of the aggregating sea anemone, 
Anthopleura elegantissima , collected a few miles north of the Golden Gate, males 
and females were shown to be distributed as unisexual aggregations on the rocks. 
The degree of gonadal development was measured by taking the gonad index 
(the ratio of volume of gonads to wet weight of anemone) every month for 
nearly 2 years (1959 and I960). This showed an annual reproductive cycle, begin- 
ning in late fall or winter, and culminating in complete spawning of the population 
in late September. 
Measurements of ovarian egg size during 1959 and I960 corresponded well 
with the cycle as expressed by the gonad index. 
Male and female cycles were not directly comparable on the basis of the gonad 
index, but identifiable males were observed over nearly the same periods as females, 
producing tailed sperm during the time when ovarian eggs were near their 
maximum size, and spawning at the same time. 
The aggregating sea anemone, Anthopleura 
elegantissima (Brandt, 1835), is one of the 
most conspicuous and abundant intertidal ani- 
mals of the Pacific coast of North America, 
ranging from Alaska to southern California. It 
is a member of the largest and most widely 
distributed family of anemones, the Actiniidae, 
Other members of the family in other parts of 
the world occupy very similar habitats in the 
same gregarious fashion. It is found firmly at- 
tached to rocks in the midtidal range from 
approximately 0-4.5 ft above mean lower low 
water level, and to higher levels where wave 
action is extreme (Hand, 1955). On the rocky 
outer coast, where it is most abundant, it occurs 
as single individuals or, most commonly, as 
aggregations of a few animals to many thou- 
sands, some of which seem interrupted only by 
the discontinuities of the substrate. It also occurs 
in bays, usually as larger, isolated individuals. 
The receding tide leaves these animals con- 
1 Formerly at Department of Zoology, University of 
California, Berkeley 4, California; present address: 
Department of Biology, Oakland City College, Oak- 
land 9, California. 
Manuscript received October 19, 1962. 
tracted into little mounds covered with bits of 
rock, shells, sand grains, and other debris held 
by adhesive papillae on the body column. 
Although abundant and conspicuous, Antho- 
pleura elegantissima has only recently been crit- 
ically described (Hand, 1955), and nothing has 
been published on its reproductive history. In 
fact, the only published detailed descriptions of 
annual gonad cycles in any coelenterates are 
those of Marshall and Stephenson (1933) on 
several reef -building qprals, and Stephenson 
(1934) on the hydroid, Myrionema | For in- 
formation on the structure and biology of sea 
anemones in general, see especially Stephenson 
(1928), and also Hyman (1940), and for a 
discussion of reproductive cycles in marine in- 
vertebrates, see the recent review by Giese 
(1959). 
The following study of reproduction in A, 
elegantissima includes ( 1 ) evidence concerning 
the distribution of males and females on the 
rocks, and (2) the annual gonad cycle. 
Acknowledgment : This paper is a thesis ac- 
cepted by the University of California in partial 
fulfillment of the requirements for the degree, 
Master of Arts. The author wishes to express 
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