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Fishery Bulletin 95(4), 1997 
individuals across age groups, 2) between individuals 
within age groups, 3) between statoliths within indi- 
viduals, and 4) within statoliths. 
For one culture of eight-day-old veligers of S. 
costatus, feeding was suspended for two consecutive 
days to induce change in statolith structure and to 
determine if changes in feeding regimen affected in- 
crement deposition. Statolith-increment numbers 
and statolith diameters (rc=10) were compared with 
those of nonstarved larvae (n=10) of equivalent age 
with two-sample /-tests (Sokal and Rohlf, 1981). 
Results 
Statoliths from Strombus costatus and S. gigas ve- 
ligers were similar in size, shape, and pattern of in- 
crement formation and were translucent in appear- 
ance. They have either a circular or elliptical appear- 
ance from a longitudinal view and a biconvex struc- 
ture in transverse section. On the basis of changes 
in size and shape, three regions are apparent (Fig. 
1). At the very center is a primordial granule, around 
which all other increments grow; newly hatched ve- 
ligers show five increments (including the primor- 
dial granule). This five-increment region (region 1) 
is quite distinct because of its lighter color, greater 
width, and seemingly dome-like nature. Prehatching 
increments in S. costatus and S. gigas had mean 
widths of 1.11 pm and 1.22 pm, respectively. Depos- 
ited around region 1 is a second, slightly darker, re- 
gion. Thinner and smaller in width, this region (re- 
gion 2) is composed of increments formed between 
hatching and completion of metamorphosis. Incre- 
ment widths corresponding to the first day after 
hatching averaged 0.33 pm for both S. costatus and 
S. gigas ; over the first six days after hatching the 
average increment width was 0.24 pm for both spe- 
cies. A third region (region 3), observed only in juve- 
niles of S. gigas, appears immediately after comple- 
tion of metamorphosis. A darker band visible at the 
outer edge of region 2 results from the even smaller 
spacings between five or six increments deposited 
just before metamorphosis. Increments correspond- 
ing to the last day before metamorphosis (age 20 
days) measured 0.09 pm on average, whereas incre- 
ments corresponding to the first day after meta- 
morphosis had a mean of 0.43 pm. Region 3 appears 
lighter than region 2, because of the wider increments. 
In both species, most veligers hatched on the sixth 
day after egg mass deposition, defined as age 0. The 
mean number of increments on the first day after 
hatching was 6.00 for S. costatus, 6.70 for S. gigas 
(Table 1). Statoliths in S. costatus show a deposition 
pattern of 1.11 increments/day (SE=0.59) over days 
A 
30 jum 
Figure 1 
Generalized structure of Strombus sta- 
toliths: (A) longitudinal view; (B) inferred 
transverse view. Numbers identify the 
three morphological regions: 1 = prehatch- 
ing, 2 = planktonic larva, and 3 = benthic 
postmetamorphic juvenile. 
0-11; in S. gigas the deposition rate was 1.13 incre- 
ments/day (SE=0.59) over days 0-9 (Table 1). In S. 
gigas this pattern continued until metamorphosis. 
For the day preceding metamorphosis (age 20 days), 
mean number of increments was 26.05; two days af- 
ter metamorphosis (age 23 days) mean increment 
number was 29.40 (Table 1). 
Significant regressions CP<0.05) were found be- 
tween age (A, in days) and mean increment number 
(I) ( S . costatus : I = 6.08 + 0.986A, r 2 =0.98; S. gigas: I 
- 6.17 + 0.984A, r 2 =0.99; data from Table 1). For 
analysis of S. gigas, we pooled locally-reared larvae 
with those brought from the Turks and Caicos. Sepa- 
rate regressions for these two sets of larvae were not 
significantly different. In the regression equations 
for both species, the slope did not differ from 1 sig- 
nificantly and the intercept did not significantly dif- 
fer from 6 (/-test, P<0.05). Thus, the equations can 
be generalized to predict strombid veliger age from 
the number of statolith increments: A = / - 6. 
