The Philippine journal of science. [Vol. 67, no. 1]

67, 4 Villadolid and Villaluz: Animals Destructive to Oysters 395

great many of the oysters in bunches heavily infested with Modiolus metcalfei die, and those that survive are stunted in growth
and possess lean meat.
POLYCLAD TURBELLARIAN
The turbellarian worm, Pseudoceros sp. (Plate 2, figs. 3 to 5)
is known among oystermen as sea wafer or leech. This animal
is thin and leaflike in shape and of a sinuous outline. The anterior margin is folded into S-shaped loops, and the posterior end
is somewhat rounded. The dorsal surface is dark brown. This
flat worm finds its way between the open valves of the oyster
and feeds upon its meat. It appears in the oyster farms in
Bacoor Bay during March and April, when the salinity of the
water is quite high.
BORING MOLLUSC
The boring mollusc, Martesia striata Linn. (Plate 2, fig. 2),
is known among oyster raisers as the boring "piddock." Its
body is cylindrical, and the shell gaping. The dorsal edge is
protected by two accessory valves, the anterior and the posterior
valves. The beaks are covered, and the siphons unite in the
form of a cylindrical tube with cilia at the end. The foot is
stout and short.
The boring molluscs are indirectly injurious to oysters. After
a brief period of free-swimming life the young burrowing shell
fish settles down for the rest of its life in a burrow bored into
the wood railings of the oyster plots (Plate 4, fig. 2). The burrows are often very near each other, so that the wood railings
are dotted with holes. The latter appear externally as small
openings, but internally the chambers are big, fitting closely
with the outline of the animal shell. The wood railings attacked
by these borers are very much weakened, and always fall to the
bottom with the loads of oysters they bear. More than one-half
of the oysters making up the oyster bunches have been observed
to die once they drop to the bottom. During the harvest season
of 1936 the oyster farmers in Bacoor Bay complained that they
were able to gather only half of the oysters raised for that year
due to the falling down of the railings attacked by these wood
borers.
BARNACLES
The barnacles (Plate 4, fig. 1) are crustaceans belonging to
the family Balanida. Those that are commonly found in Bacoor
Bay are Balanus rostratus Hoek. The shells are almost smooth