The Folliculinids (Protozoa) of Ago Bay, Japan, and Their Relation 
to the Epifauna of the Pearl Oyster ( Pinctada mart ensii J 1 
Donald C. Matthews 2 
Although the pearl oyster ( Pinctada 
martensii) is widely dispersed throughout Jap- 
anese waters, that portion of Honshu south of 
Toba, in the many bays of Ise peninsula, excels 
as a favorable production center. This is largely 
because the cold Oya Shio (current) flowing 
south from the Kurile Islands meets the warm 
Kuro Shio between 35° and 40° N, sinks, and 
passes under it to well up again farther south, 
bringing an abundance of plankton. Thus, pro- 
tected bays such as Ago, Matoya, and Gokasho 
provide an excellent environment for oysters and 
other Alter- feeders to multiply. However, as the 
number of animals in the epifauna increases, 
available attachment sites decrease, and a se- 
quential, complex epifauna develops on any 
suitable surface, whether glass plates or P. 
martens'll imbricate scales. 
Whereas some 50 species embracing many 
taxa (Protozoa, Porifera, Coelenterata, Nemer- 
tini, Nematoda, Polychaeta, Ostracoda, Harpac- 
tida, Cumacea, Amphipoda, Decapoda, Pycno- 
gonida, Bryozoa, Mollusca, Echinodermata, and 
Tunicata) comprise this complex epifauna, the 
Polychaeta in particular, by the number and 
depth of their burrows, seriously affect the 
oysters’ well-being. 
Korringa (1951) working on the epifauna of 
Ostrea edulus in the Oosterschelde, Holland, 
mentioned in his annotated list of species that 
folliculinids are among the first to appear, and 
he reasoned that because their growth and re- 
production are so rapid they ". . . may be 
important as basic food for many members of 
the oysters’ epifauna.” Although Miyazaki 
(1938) made an extensive study of fouling 
organisms on shell-strings hung from rafts of 
Japanese oyster farms, interrelationships of 
species were not studied in detail. 
1 This study was supported in part by Grant No. 
G.F. 200 from the National Science Foundation. Manu- 
script received April 13, 1967. 
2 Department of Zoology, University of Hawaii, 
Honolulu, Hawaii 96822. 
The purpose of this paper is twofold: (A) to 
report the occurrence of folliculinids in Ago 
Bay, and (B) to determine whether folliculinids 
serve as food for P. martensii epifauna. 
FOLLICULINIDS IN AGO BAY 
Materials and Methods 
In a combination of the methods of Moebius 
(1887), Miyazaki (1938), and Matthews 
(1962), shell collectors were suspended at 
various depths in Ago Bay from June through 
November, 1965, and sequential fouling peri- 
odically examined. Concurrently, folliculinids in 
the epifauna of living P. martensii, Pinna at- 
tenuata, and Chlamys nohilis suspended in 
baskets approximately one meter below oyster 
rafts of Ago Bay were similarly studied. Those 
readily identifiable folliculinids were figured 
and recorded, others were preserved and shipped 
to Honolulu for subsequent identification. 
Results 
The following folliculinids were obtained: 
Ascohius sileni Hadzi, 1951, Slovenica Biology 
2:114-122. 
Folliculina simplex (Dons) Silen, 1947, Ark. 
Zool. 39(12) : 5 3-5 6, figs. 62-65. 
Figure 1 A represents a ventral view of A. 
sileni taken at Ago Bay, June 21, 1965 from 
narrow cracks in the shells of Spirorbis sp. In 
such restrictive sites, the dorso-ventrally flat- 
tened lorica (/) seems attached throughout its 
length by a rather copious collectoderm (<7). 
The lorica tapers rather gradually from its 
mouth (c) (almost devoid of collar) to the 
rounded and rather broad proximal end. Figure 
1 B represents a lateral view (left side) of A. 
sileni taken at the same time from spiral "chim- 
neys” of the delicate, coral-like Bryozoan, 
Bugula dentata (Lamouroux) (see Utinomi, 
1961:33, pi. 17, fig. 6) and from the smooth, 
"vertical” sides of Spirorbis sp . where attach - 
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