Vol. 6; Supplement
Page 63
THE VELIGER
FRETTER, VERA, & ALASTAIR GRAHAM
3. Repairs to shells damaged mechanically, by filing
1962. British prosobranch molluscs; their functional anatomy
the aperture, grinding holes in the body and upper
and ecology. London, Ray Soc.; xvi + 755 pp.; 317 figs.
whorls, and by cracking in a vise are described.
JOHNSON, T. W., Jr. & W. A. ANDERSON
1962. A fungus in Anomia simplex shell. Journ. Elisha Mit-
LITERATURE CITED
chell Sci. Soc. 78: 43 -47
BONAR, L.
MCGEE, PATRICIA
1936. An unusual ascomycete in the shells of marine animals.
1964. A new pigment from Tegula funebralis (Mollusca: Gast¬
Univ. Calif. Publ. Bot. 19: 187 -194
ropoda). The Veliger 6; Supplement: 25 - 27; 1 text fig.
The Dispersal of Young of the Commensal Gastropod
Crepidula adunca from its Host, Tegula funebralis
DEBORAH A. PUTNAM
Hopkins Marine Station of Stanford University,
Pacific Grove, California
(4 Text figures)
INTRODUCTION
HATCHING
Crepidula adunca SowERBy, 1825 is a protandric marine
Crepidula adunca breeds the year round (MORITz, 193
prosobranch commonly found on the shells of Tegula
The animals used were gathered from Mussel Point,
funebralis (A. ADAMS, 1854), both when the latter is
Pacific Grove, California. Tegula funebralis with the
occupied by the snail and when it is occupied by Pagurus
brooding Crepidula females were kept in glass finger
spp. MORITZ (1938) gives the range of C. adunca as
bowls at 12 to 18° C. Young when hatched were kept
being similar to that of T funebralis: from Vancouver,
similarly. All young used in all experiments were hatched
British Columbia, to the tip of Lower California. CONK¬
without human assistance, both to avoid harming the
LIN (1897) has followed the cell lineage of C. fornicata
young through attempts to liberate them artificially
and C. plana, and MoRrrz (1938, 1939) has treated the
and to establish their age, as the period of development
anatomy and organogenesis of C. adunca.
to hatching is not known.
Crepidula adunca undergoes a very direct develop¬
In the four cases where hatching was observed, young
ment from large, yolky eggs which are brooded by the
Crepidula adunca were released between 8:30 and 10:30
female. The hatching young crawl out of the egg cases
a. m. The egg cases are attached by individual stalks to
as juveniles which are similar to adults. At hatching there
one spot on the Tegula funebralis shell, immediately
may be from 150 to 200 young released. Although no
ventral and posterior to the head and anterior to the foot
pelagic stage is present, the adult population of C. adunca
of the female C. adunca. Normally, the female’s shell
is quite well dispersed over the Tegula funebralis popu¬
is lifted no more than 0.5 mm above the substrate, only
lation near the Hopkins Marine Station, Pacific Grove,
enough to allow water to flow through the mantle cavity
California. The number of adult C. adunca per T. funeb-
for filter-feeding and respiration. During hatching, how¬
ralis shell is relatively low (eight was the maximum
ever, the female intermittently lifts her shell 1 to 3 mm
number seen) as compared to the large number of young
above the substrate, for periods which varied from 3.5
per brood. Clearly, the young become dispersed to new
seconds to about 4 minutes. Then with a forward and
hosts without benefit of a pelagic stage. How this is
downward motion of her head over the egg cases, the
female pushes out those of her young which are loose
accomplished is the subject of the present investigation.
Vol. 6; Supplement
Page 64
THE VELIGER
The young which fall off sink to the bottom. Mucus
and in the path of her head. Other hatched young
adhering to the young affects the rate of sinking, which
may crawl out. The young usually escape from the
ranges from about 1.1 to 2.6 cm/sec (average 1.4 cm/sec)
anterior region of the mother’s shell, which is typically
Once off the host, the young are quite active. Their move¬
oriented on the host as shown in Figure 1.
ment seems random; they are neither attracted to nor
repelled by each other. There is a net movement upward
and towards a light, if this is not too intense. These
actions may even lead the spat to crawl out of the water,
where they dessicate and die within 15 to 20 minutes on
a sunny day. It is perhaps an advantage, therefore, for
L
the newly hatched spat to be washed off the host Tegula


funebralis, which is normally exposed during the tidal
cycle. Sunlight alone has no effect on the newly hatched
Crepidula adunca when they are immersed.



The spat are very active even in still water, and their
random movements tend to disperse them. Simple dis-
persal experiments were carried out in eight finger bowls
with newly hatched young. Ten juveniles were placed in
the center of each bowl and their positions marked on
a grid at five minute intervals. Average motility, based on

these runs, is plotted in Figure 2. Maximum rate of loco¬
motion measured over a short distance was about 0.2
mm/sec.
0
Figure 1: Orientation of Crepidula adunca
on Tegula funebralis.
The egg cases themselves may be expelled immediately
at the end of hatching, which takes approximately one
half hour, or after several days. Not all egg capsules
under a given female are necessarily at the same stage of
development or hatch at the same time.
THE NEWLY HATCHED YOUNG
22
The average newly hatched Crepidula adunca, based on
the measurement of six broods, is 1.19 mm long and
10 15 20 25
0.91 mm wide. The spat when hatched are very motile.
Minutes
They show no tendency to avoid either the mother or the
host; however, many of the spat fall off the Tegula funeb-
Figure 2: Average net distance covered by young
ralis immediately. The number of spat leaving the host is
Crepidula adunca.
increased by any current present; mucus still covers the
spat, and they do not adhere well to any surface. Less
A weak current of water stimulates the spat, which
than ten percent of a brood remain on the parental host
tend to orient upstream and move into the current. In
stronger currents the spat clamp down and remain immo¬
even in still water, where the only motion is that resulting
from the creeping of T. funebralis. The few young re¬
bile unless torn loose by the current. The ability of spat
maining on the host become quiescent sooner and remain
to cling in currents of varying rates of flow is shown in
Figure 3.
so longer than those which fall off.
Vol. 6; Supplement
Page 65
THE VELIGER
RESPONSES OF JUVENILE Crepidula adunca
TOWARD Tegula funebralis AND ADULT
————- Empty Tegula funebralis shell
Crepidula adunca
— 2 Male Crepidula adunca
Preliminary experiments indicated that adult female
—.—.— Female Crepidula adunca
Crepidula adunca, removed from their hosts, usually
attempted to climb back on, and that adult males are
----
attracted by Tegula funebralis, but even more strongly by
female C. adunca. In contrast, the newly hatched spat
do not appear to be strongly attracted either to T. funeb¬

ralis or to older C. adunca, male or female. The reactions
8

-—
of juveniles to parents and host were tested as follows.
—-—-—-—-—-7

oV
O I 23 4 5 6 7 8 9 10 I 12
8100-
Days after hatching
2 80
Figure 4: Settlement of spat on various substrates.
an occupied T funebralis shell than an empty one,
presumably due to the comparatively rapid motion of
540
the larger snail.
The attraction to Tegula funebralis must increase as
2 20.
spat grow older, since the adult population lives on this
host and shows a clear positive response to it. However.
5 o
this investigator found no Crepidula adunca smaller than
20 30 40 50 60 70
0
3.8 mm in length, 2.8 mm in width and 2.0 mm in height
Rate of flow (ml./cm 2/sec.)
on a T funebralis in the field. Searches for spat or young
adults on rocks, in shells and gravel, and on algae were
Figure 3: Ability of juvenile Crepidula adunca to cling
unsuccessful
to a glass surface in a current. Up to 34 ml/cm’/sec flow,
Adult Crepidula adunca are filter-feeders. However,
random movement continued, with a slight net orienta¬
the ciliated food groove does not appear until after
tion into the current. Above this, the spat clamped
hatching, nor does the food pouch develop until after
down tightly.
the young adult stage (MoRITz, 1939). Scraping motions
with the radula in the young have been observed, which
len newly hatched young were placed in the center of
strongly suggests that the spat may obtain microscopic
each of four finger bowls. To each of three bowls was
food by this means. The young might not be strongly
added, near the edge, one of the following: 2 living male
attracted to Tégula funebralis or to another, older C.
C. adunca, an empty T funebralis shell, or a living female
adunca until their filter-feeding apparatus has developed.
C. adunca. The fourth bowl served as a control. The po-
SUMMARY
sitions of the young free in the bowls or on the various
proffered substrates were recorded daily for a period of
Crepidula adunca is a protandric marine prosobranch
twelve days (Figure 4).
commonly found on the shells of Tegula funebralis. Female
There is no evidence that the spat are attracted to
C. adunca are oriented in a consistent manner on the
légula funebralis or Crepidula adunca. Instead, the
whorls of the T. funebralis shell. There is no free-swim-
young appear to move at random. However, when the
ming larval stage; the brooded young crawl or are pushed
come in contact with any one of these shells, they crawl
out from under the mother as juveniles similar in form
upon it, and their motility thereafter is greatly decreased.
to the adults. The newly hatched spat are very motile;
The presence of the living animal is not a factor; as many
the great majority drop off the host and sink. Weak
settle on an empty C. adunca shell as on one that is
water currents stimulate the spat; there is net orientation
occupied. In supplementary experiments fewer settled on
into current, against gravity, and toward moderate light.
Page 66
Vol. 6; Supplement
THE VELIGER
Spat are only weakly attracted to either T. funebralis or
older C. adunca; this attraction is clearly present in older
individuals.
LITERATURE CITED
CONKLIN, E. G.
1897. The embryology of Crepidula.
Journ. Morph.13:
1-226; plts. 1 -9; 13 text figs.
MORITZ, CHARLES E.
1938. The anatomy of the gasteropod Crepidula adunca
SOWERBY. Univ. Calif. Publ. Zool. 43: 83 - 92; 6 text figs
1939. Organogenesis in the gasteropod Crepidula adunca
SOWERBY. Univ. Calif. Publ. Zool. 43: 217 - 248; 22 text figs
Studies on the Commensal Limpet Acmaea asmi
in Relation to its Host, Tegula funebralis
ARTHUR B. EIKENBERRY JR.
AND
DIANE E. WICKIZER
Hopkins Marine Station of Stanford University,
Pacific Grove, California
Text figures; 2 Tables)
with its host and both organisms were measured. Notation
Acmaea asmi (MDDDENDORFF, 1849) is a stenotopic lim
of horizontal and vertical position was made.
pet which inhabits the rocky intertidal, and lives almost
Since the five transects varied both in length and in
exclusively on Tegula funebralis (A. ADAMS, 1854). By
slope, horizontal distribution in terms of absolute distance
studying distribution in relationship to horizontal and ver-
from shore is not particularly significant. However, in
tical position in the intertidal and by considering dis
all five transects populations were concentrated in the
tribution in relationship to food and substrate preferences
middle areas, the regions affected neither by shore line
we hoped to establish a clearer understanding of the adult
wave action nor the wave battering of the outer intertidal.
commensal relationship between A. asmi and T. fune¬
bralis. The following work is a continuation and refine
Furthermore, observations at high tide (WARA &
ment of studies carried out by FREDERICK H. TEST in
WRIGHT, 1964) revealed a qualitative difference in wave
1945, and RUTH RADFORD in 1959.
action between the transects and showed that the num-
TRIBU
ION
ber of Acmaea asmi was generally inversely proportional
During April and May, 1963, distribution of Acmaea asmi
to the wave battering received by the area. Qualitatively,
was studied along Mussel Point on Monterey Bay, Cali
Area B had very heavy wave action and no A. asmi were
found; Area A received a heavy battering and the density
fornia. Every A. asmi noted along five transects by W.
of A. asmi was low. As the wave action decreased from
WARA & B. WRIGHT (1964, see Figures 1 - 5) was collected