PLANKTON OF THE WOODS HOLE REGION 
147 
CIREIFEDIA 
At certain seasons of the year barnacle larvte are very abundant in the plank- 
ton. In both the nauplius and "cypris" stages they swim freely, although as a rule 
the "cyprids" settle on the Fucus soon after the metamorphosis and are not taken 
in large numbers in surface collections. At such times often thousands can be 
taken in a single sweep of a hand net drawn through the Fucus near the water's 
edge. The nauplii of the three species of Balanus are so much alike that even 
the most careful identification is often rather uncertain. However, the difference 
in the breeding periods makes the identification easy in the field, although in certain 
years the seasons of Balanus crenatus and B. eburneus overlap. 
Balanus crenatus is not as abundant in the immediate vicinity of Great Harbor 
as are the other species of the genus, and for that reason the larvae occur in much 
smaller numbers in surface collections. The breeding season starts early in June 
and generally continues until the middle of July. In 1922 (fig. 48) the first larvae 
Fig. 48. — Occurrence of barnacle larvae in surface Fig. 49. — Occurrence of barnacle larvae in surface collections 
collections from June to December, 1922. of 1923. , Balanus balanoides nauplii; , B. 
, Balanus balanoides; , B. balanoides "cyprids"; , B. crenatus; _.— , 
crenatus; — . — , Chthamalus stellatus; , B. eburneus; +, Chthamalus stellatus 
B. eburneus; + , Lepas sp. 
appeared on July 2; the last on July 16. They were abundant on only one day — 
July 13. After this a single specimen was taken on July 15 and one on July 16. 
It is possible that nauplii may have occurred after August 1, when fairly large num- 
bers of B. eburneus suddenly appeared. However, as an interval of 15 days elapsed 
between the two periods, the possibility of a stray B. crenatus nauplius being present 
would probably be so small that it need not be considered. In 1923 the first speci- 
men appeared on June 29 (fig. 49). Scattered nauplii and "cyprids" were taken 
until July 23. Off Coney Island, N. Y., swarms of early nauplii (no doubt B. 
crenatus) were taken on June 12, 1923. 
Balanus eburneus is usually found in August, although the nauplii seldom form 
an important part of the surface collections. This may be due to the fact that the 
summer plankton is particularly rich and the barnacles, therefore, are greatly 
outnumbered. It is certain, however, that they never appear in such swarms as 
does B. balanoides. The first nauplii in 1922 (fig. 48) appeared on August 1, scat- 
