NOAA Technical Report NMFS 50 March 1987

Preparation of Acetate Peels

of Valves from the Ocean Quahog,

Arctica islandica,

for Age Determinati,ons

John W. Ropes

u.s. DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

National Marine Fisheries Service
NOAA TECHNICAL REPORT NMFS

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5285 Port Royal Road. Springfield, VA 22161. Although the contents have not been copyrighted and may be reprinted entirely, reference to source is appreciated.

13. Guidelines for reducing porpoise mortality in tuna purse seining, by James M.

Coe, David B. Holts, and Richard W. Butler. September 1984, 16 p.

14. Synopsis of biological data on shortnose sturgeon, Acipellser brevirostrum

LeSueur 1818, by Michael J. Dadswell, Bruce D. Taubert, Thomas S. Squiers, Donald

Marchette, and Jack Buckley. October 1984, 45 p.

15. Chaelognatha of the Caribbean sea and adjacent areas, by Harding B. Michel.

October 1984, 33 p.

16 Proceedings of the Ninth and Tenth U.S.-Japan Meetings on Aquaculture, by

Carl J Sindermann (editor). November 1984, 92 p.

17 IdentificatIOn and estimation of size from the beaks of 18 species of cephalopods

from the PaCific Ocean, by Gary A. Wolff. November 1984, 50 p.

18. A temporal and spatial study of invertebrate communities associated with hardbottom habitats in the South Atlantic Bight, by E. L. Wenner, P. Hinde, D. M. Knott,

and R. F. Van Dolah. November 1984. 104 p.

19. Synopsis of biological data on spottail pinfish, Diplodus holbrooki (Pisces:

Sparidae), by George H. Darcy. January 1985, 11 p.

20. Ichthyoplankton of the Continental Shelf near Kodiak Island, Alaska, by Arthur

W. Kendall, Jr., and Jean R. Dunn. January 1985, 89 p.

21. Annotated bibliography on hypoxia and its effects on marine life, with emphasis

on the Gulf of Mexico, by Maurice L. Renaud. February 1985, 9 p.

22. Congrid eels of the eastern Pacific end key to their Leptocephali, by Solomon

N. Raju. February 1985, 19 p.

23 Synopsis of biological data on the pinfish, Lagodoll rhomboides (Pisces:Sparidae),

by George H. Darcy. February 1985, 32 p.

24. Temperature conditions in the cold pool 1977-81: A comparison between southern

New England and New York lransects, by Steven K. Cook. February 1985, 22 p.

25. Parasitology and pathology of marine organisms of the world ocean, by William

1. Hargis, Jr. (editor). March 1985, 135 p.

26. Synopsis of biological data on the sand perch, Dip/ectrum formosum (Pisces:

Serranidae), by George H. Darcy. March 1985,21 p.

27. Proceedings of the Eleventh U.S.-Japan Meeting on Aquaculture, Salmon

Enhancement, Tokyo, Japan, October 19-20, 1982, by Carl J. Sindermann (editor).

March 1985, 102 p.

28. Review of geographical stocks of tropical dolphins (Stellella spp. and Delphillus

delphis) in the eastern Pacific, by William F. Pernn, Michael D. Scott, G. Jay Walker,

and Virginia L. Casso March 1985, 28 p.

29. Prevalence, intensity, longevity, and persistence of Allisakis sp. larvae and Laeistorhynchus tenuis metacestodes in San Francisco striped bass, by Mike Moser, Judy

A. Sakanari, Carol A. Reilly, and Jeannette Whipple. April 1985, 4 p.

30. Synopsis of biological data on the pink shrimp, Pandalus borealis Krl>yer, 1838,

by Sandra E. Shumway, Herbert C. Perldns, Daniel F. Schick, and Alden P. Stickney.

May 1985, 57 p.

31. Shark catches from selected fisheries off the U.S. east coast, by Emory D. Anderson, John G. Casey, John J. Hoey, and W. N. Witzell. July 1985, 22 p.

32. Nutrient Distributions for Georges Bank and adjacent waters in 1979, by A. F.

J. Draxler, A. Matte, R. Waldhauer, and J. E. O'Reilly. July 1985, 34 p.

33. Marine flora and fauna of the Northeastern United States. Echinodermata:

Echinoidea, by D. Keith Serafy and F. Julian Fell. September 1985,27 p.

34. Additions to a revision of the shark genus Carcharhinus: Synonymy of Apr/onodon and Hypoprion, and description of a new species of CarclUlrhinus (Carcharhinidae),

by J. A. F. Garrick. November 1985, 26 p.

35. Synoptic review of the literature on the Southern oyster drill Thais haemastomCi

j/oridalla, by Philip A. Butler. November 1985, 9 p.

36. An egg production method for estimating spawning biomass of pelagic fish:

Application to the northern anchovy, Ellgraulis mordax, by Reuben Lasker (editor).

December 1985, 99 p.

37. A histopathologic evaluation of gross lesions excised from commercially important North Atlantic marine fishes, by Robert A. Murchelano, Linda Despres-Patanjo,

and John Ziskowsld. March 1986, 14 p.

38. Fishery atlas of the northwestern Hawaiian Islands, by Richard N. Uchida and

James H. Uchiyama (editors). September 1986, 142 p.

39. Survey of fish protective facilities at water withdrawal sites on the Snake and

Columbia Rivers, by George A. Swan, Tommy G. Withrow, and Donn L. Park. April

1986, 34 p.

40. Potential impact of ocean thermal energy conversion (OTEC) on fisheries, by

Edward P. Myers, Donald E. Hoss, Walter M. Matsumoto, David S. Peters, Michael

P. Seld, Richard N. Uchida, John D. Ditmars, and Robert A. Paddock. June 1986,

33 p.

41. A stationary visual census technique for quantitatively assessing community struc·

ture of coral reef fishes, by James A. Bohnsack and Scott P. Bannerot. July 1986, 15 p.

42. Effects of temperature on the biology of the northern shrimp, Pandalus borealis,

in the Gulf of Maine, by Spencer Apollonio, David K. Stevenson, and Earl E. Dunton,

Je. September 1986, 22 p.

43. Environment and resources of seamounts in the North Pacific, by Richard N.

Uchida, Sigeiti Hayasi, and George W. BoehJert (editors). September 1986, 105 p.

44. Synopsis of biological data on the porgies, Calamus arctiJrons and C. proridens

(Pisces: Sparidae), by George H. Darcy. September 1986, 19 p.

45. Meristic variation in Sebastes (Scorpaertidae), with an analysis of character associa·

tion and bilateral pattern and their significance in species separation, by Lo-chai Chen.

September 1986, 17 p.

46. Distribution and relative abundance of pelagic 110nsalmonid nekton off Oregon

and Washington 1979-84, by Richard D. Brodeur and William G. Pearcy. December

1986, 85 p.
NOAA Technical Report NMFS 50

Preparation of Acetate Peels

of Valves from the Ocean Quahog,

Arctica islandica,

for Age Determinations

John W. Ropes

March 1987

u.s. DEPARTMENT OF COMMERCE

Malcolm Baldrige, Secretary

National Oceanic and Atmospheric Administration

Anthony J. Calio, Administrator

National Marine Fisheries Service

William E. Evans, Assistant Administrator for Fisheries
The National Marine Fisheries Service (NMFS) does not approve, recommend

or endorse any proprietary product or proprietary material mentioned in this

publication. No reference shall be made to NMFS, or to this publication furnished by NMFS, in any advertising or sales promotion which would indicate

or imply that NMFS approves, recommends or endorses any proprietary

product or proprietary material mentioned herein, or which has as its purpose

an intent to cause directly or indirectly the advertised product to be used or

purchased because of this NMFS publication.

ii
CONTENTS

Introduction 1

Procedures 2

Processing-time economies 3

Identity of annuli 3

Summary 4

Citations 5

III

Preparation of Acetate

Peels of Valves from

the Ocean Quahog,

Arctica islandica,

for Age Determinations

JOHN W. ROPES

Northeast Fisheries Center

Woods Hole Laboratory

National Marine Fisheries Service, NOAA

Woods Hole, MA 02543

ABSTRACT

Techniques are described for preparing acetate peels ofsectioned valves of ocean

quahogs, Arctica islandica, for age determinations. The respective sequence of

preparation begins by sectioning left valves oriented to include a single hinge tooth,

bleaching to remove the heavy periostracum, embedding the valves in an epoxy

resin, grinding and polishing the embedments to a high luster, etching the exposed cut valve surfaces, and applying sheet acetate with acetone. Annuli are clearly defined relative to growth increments in the peel preparations for all sizes and

ages of ocean quahogs.

INTRODUCTION _

Bivalve molluscs have historically been aged by examining the

external valve surfaces for dark growth "rings" or "bands" that

form as an annual periodic event (Weymouth 1923; Stevenson and

Dickie 1954; Wilbur and Owen 1964; Merrill et al. 1966; Feder

and Paul 1974). Ring formation has been associated with factors

having probable effect on the metabolism of growth, such as extrinsic environmental conditions (temperature) or intrinsic conditions (spawning). In applying the method to some species, however, conflicting or incomplete age estimates may be obtained. This

is particularly true for the ocean quahog, Arctica islandica Linne,

a species with a potentially very long life history (Thompson et al.

1980a). Small ocean quahogs «60 mm in shell length) often exhibit definite external rings useful in measuring growth and determining age. Some of the rings formed in the earliest years of the

life of a large ocean quahog may be discernible, but those near the

ventral valve margin usually become crowded together, and often

the overall periostracum is black in color. Separation of the rings

is impossible, even under magnification, and erosion of the shell

surface in the umbonal area often obliterates the youngest rings.

In some bivalve species, internal narrow dark growth lines (hereafter termed annuli) alternating with broad light growth-increment

deposits are seen in the broken edges of valves. The annuli have

continuity with rings on the external valve surface. Development

of diamond-impregnated saw blade equipment has greatly facilitated

sectioning bivalve shells in a directed manner for an examination

of the accretion of shell layers from the beginning of their formation at the umbo to the ventral margin. Although sectioning the valve

is a time-consuming procedure, it permits an examination of the

internal depositional features. These tend to be much less affected

by destructive external environmental conditions impacting on the

valve surfaces and, thus, a record of growth is preserved intact.

Annual microstructural deposits may also occur in other parts of

the shell that can be prepared for examination by fairly rapid

methods, e.g., the chondrophores of the surf clam, Spisula solidissima (Dillwyn) (Ropes and O'Brien 1979).

Simply cutting the valves of a bivalve may not expose well-defmed

annuli, due to variations in the microstructure of the shell deposits.

Such is the case for ocean quahogs. Kummel and Raup (1965)

developed techniques for fossil bivalves involving preparation of

the cut valve surfaces and transfer of the microstructural details

onto sheet acetate.

The objectives in the development of procedures for ocean quahogs were that age/growth characteristics be determined precisely

and efficiently. Assessment surveys of the population can provide

large numbers of specimens for analysis, from 1,500-2,500 per

survey. This paper describes procedures developed at the Northeast Fisheries Center for the preparation of acetate peels of sectioned bivalves. It is the only known technique at present for

accurately determining the age of ocean quahogs, and more clearly exposes annuli in younger specimens than examination of the

external valve surface. It also has potential application for other

difficult-to-age bivalves.
DORSAL

PROCEDURES __

ANTERIOR

Jt!~,------ Tooth

VENTRAL

DIRECTION OF CUT

/

;:;;~:;~~- Umbo

Hinge ligament ----...

Palliof line -J

POSTERIOR

Sample information is recorded for each ocean quahog preliminary

to preparing the valves for aging. A sequential code number is inscribed on each valve of a pair, single valve, or piece of a valve.

Measurements of length (the longest antero-posterior dimension),

height (the deepest dorso-ventral dimension), width (the widest

lateral dimension), and dry weight are made of paired, whole valves

to 0.1 mm with vernier calipers, and weight to 0.1 g. Figure 1 shows

the features of an ocean quahog valve for orientation purposes in

measuring and sectioning operations.

Figure I-Sketch of internal valve features and direction of cut (dashed line) to

completely section the left valve of an ocean quahog, Arctica islandica. The anterior

portion of the valve is retained for subsequent processing.

Figure 2-C1ose-up view of the left vatve of an ocean quahog, Arctica islandica,

fastened to the adjustable arm ofthe saw unit and orieuted with the tooth (arrow)

beside the diamond blade.

strength household bleach for a few hours (Table 1). Each valve

is periodically inspected and removed as soon as the periostracum

is dissolved away. A rinse in tap water completes this step. Precautionary procedures for minimizing the destruction of ultrastrucTable I-Sources of apparatus and materials.

The left valve of a pair is selected for sectioning, since it has

a single prominent tooth in the hinge. The tooth contains annuli

for exposure during the sectioning operation of the valve. Each valve

is marked on the ventral margin at a point from the posterior end

equal to one-third of the valve length. This orients sectioning through

the umbo and parallel to the broadest tooth surface.

The valve is fastened firmly to the adjustable arm holder of the

saw unit by a sticky, putty-like material (Slab-Stick) with its concave, inner surfaces toward a diamond-impregnated saw blade (Fig.

2, Table I). The valve is oriented with the tooth toward the front

of the saw machine and is positioned to cut from the mark on the

ventral margin through the middle of the tooth, or immediately

beside the posterior edge of the tooth. This latter orientation is

necessary for small valves, since the small-sized tooth would be

destroyed by the cut of the saw blade. Upon nearing completion

of the cut through the valve, thumb pressure applied beneath the

adjustable arm holder lessens the weight of the valve, and avoids

breakage and saw blade damage. This procedure minimizes such

problems by focusing the operator's attention on the cutting action

of the saw. The anterior portion of the valve is saved for later treatment. About 7-8 medium sized (60-70 mm long) or 3-4 large sized

(100+ mm) Arctica can be cut per hour at 300 rpm of the saw blade.

No more than the heaviest weight (150 g) provided for the saw

machine is used on the adjustable arm for large clams; the medium

weight (75 g) for medium clams; and the lightest weight (25 g) for

small clams. Excessive weight is avoided, since this can warp the

blade or break the valve.

Aragonitic granules (a form of calcium carbonate) in the periostracum of ocean quahogs dissolve during a later etching step. leaving voids at the edge of valve peel preparations that distort the peel

image (Ropes et aI. 1984). This covering is therefore removed by

immersing the sectioned cut surfaces in a shallow solution of fullSource

Buehler Ltd.

41 Waukegan Road

P.O. Box 1

Lake Bluff, IL 60044

Commercial Plastics & Supply Corp.

352 McGrath Highway

Sommerville, MA 02143

Miller Stephenson Chemical Co., Inc.

P.O. Box 950

Danbury, CT 06810

Pigment Dispersions, Inc.

54 Kellogg Court

P.O. Box 412

Edison, NJ 08818

Raytech Industries, Inc.

P.O. Box 6

Stafford Springs, CT 06075

Local markets

Apparatus or material

Isomet Low Speed Saw

Diamond Wafering Blades

(4" & 5" dia., high concentration)

Di-acetate sheets 19x24xO.OO5"

thick

Epan 815 and DTA hardener

#230 I blue pigment

Hustler Vibrating Lap 15" dia.

Slab-Stick

Ray-Tilt 6" Gem Maker Grinding

Machine

Bleach (sodium hypochlorite ca.

5.25%)

Norton, Tufuak, Durite, Waterproof paper, Closekote, Silicon

Carbide

2
tural details by extended exposure of molluscan shells to bleach

have been outlined by Carriker (1979).

Some grinding of the cut surfaces is advisable before further processing, if saw marks or other unwanted blemishes are evident, or

if the saw cut was not close to the tooth. Careful handling is important in this step to minimize chipping of the cut valve edge. Carbide paper of two successively finer grits (240 and 400) is used

for grinding and water is used on the paper to wash away particles

(Table I). About 15 min per specimen may be spent in this grinding operation. After thoroughly rinsing the valves in tap water, they

are allowed to dry.

An epoxy resin is used for support of the valves during subsequent polishing operations (Table 1). The resin, hardener, and a

colored pigment are carefully but thoroughly mixed (ca. 1 min),

avoiding the introduction of bubbles, and in small amounts (50-75

mL) to minimize heat due to an exothermic reaction between the

resin and hardener. The pigment added to the clear epoxy serves

as a background, contrasting color with the white valves in a later

grinding operation. The mixed epoxy is poured into plastic- or

paraffin-coated molds to a depth of about liz cm. When lowering

a valve into the epoxy, the cut surface is pressed down onto the

mold bottom to force out bubbles. Some bubbles may adhere to

the valve surfaces, and if they are not removed may distort the

acetate peel impression. These can be dislodged with the stirring

stick used to mix the epoxy, but subjecting the set-up to the pressure of a vacuum chamber for an hour usually evacuates bubbles

that may not be easily detected. After an overnight hardening period,

the embedded valves are removed from the molds.

Three successively finer grits (240, 400, and 600) of carbide paper

are then used to obtain a flat, smooth surface on the embedded cut

surfaces of the valves. Most of the grinding is done with the 240

grit paper to remove epoxy and to expose the broadest area of the

tooth; the finer grits (400 and 600) are used to minimize scratches

from the coarser grit papers. Hand grinding tends to produce optimal

results, because frequent inspection can be made of the progress

of grinding; however, a grinding machine has proven to be faster

(Table I). Usually only the 240 grit is used on the machine to remove

excess epoxy, followed by hand grinding to remove the circular

and deep scratches that may have been produced by the machine.

About 15-30 min per specimen may be spent exposing the tooth

and valve surfaces. The pigment in the epoxy helps in determining

the desired level of exposure of the cut surface. This initial grinding prepares the embedded valves for the final polishing steps.

A blemish-free, high-gloss surface on the cut valve surfaces is

required and is produced on a vibrating lap machine in two steps

(Table 1). In the first step, the pad lining the bottom of an attachable pan is flooded with tap water and drained. After clamping the

pan on the machine, the pad is charged with about one teaspoon

of #2 medium grit powder, the specimen is placed on the pad, and

the machine is turned on. During a 1-2 hour period, the specimen

is occasionally removed, rinsed off in tap water, damp-dried, and

inspected for a moderate sheen. In the second step, the specimen

is transferred to a similar pan flooded with water, but the pad is

charged with fine grit (#3) powder. The valves are polished an additional 1-2 hours; more grit powder added after one hour hastens

polishing. A final high gloss is most evident on the cut valve surface, but less so on the epoxy surface. A thorough washing in tap

water removes traces of grit.

The polished block face is then placed in or flooded with a I %

HCI solution for one minute to etch the valve surfaces and rinsed

in tap water, taking care not to damage the etched surfaces. After

drying the block, code numbers for each valve are scribed with

3

a carbide-tipped pen into the epoxy near the cut valve surfaces.

These numbers are automatically transcribed onto the acetate peel

during the next step.

Acetate peels are made by supporting the etched block with the

surfaces uppermost and level. An acetate sheet is laid over the surface and a binder clip is used to hold it at one end (Table 1). The

other end of the sheet is then lifted and acetone is pipetted onto

the specimen while lowering the sheet. Acetone must flood completely between the sheet and block surface without bubbles for a

successful peel. After draining of excess acetone, the whole block

is turned over, laid on a pad of paper, and pressed for about one

minute. After a one-hour drying period, the acetate is peeled off.

The peels are sandwiched between glass slides for examination

under a light compound microscope, although the image may also

be projected onto the screen of a fish-scale microprojector. Additional peels can be made by simply applying a new sheet of acetate

and acetone to the specimen. A sheet of acetate left on the block

protects the specimen from damage.

Processing-time economies

Sectioning the valves before embedding them is a departure from

the technique described by Kennish et al. (1980), since it permits

more certain orientation of a valve over the saw blade. It also speeds

sectioning because there is no epoxy to cut through. Kennish et al.

(1980) warned that unembedded valves may be fractured. Such

damage to ocean quahogs was minimized by careful handling of

the fairly robust valves. Individuals as small as 10 rom in shell length

have been successfully prepared for aging.

Other modifications economize on time and materials. since there

is a need to be efficient in the preparation process. Two saws have

been used during the sectioning step. Unembedded, sectioned valves

were polished and etched in an attempt to eliminate the embedding

step, but the peels were distorted by acetate melting over the valve

edges. This resulted in incomplete peel images at the valve edges.

To further speed the process, groups of valves are placed in the

bleach solution. Sectioned valves are lowered edge-first into a

shallow depth of epoxy rather than embedding a whole valve. This

permits grouping more than one valve (up to 3-4) in a single mold.

The group of embedded valves is also more easily handled during

the later grinding/polishing, etching, and peel steps.

Identity of annuli

Acetate peels of many marked ocean quahogs recovered in subsequent years have been prepared, since these individuals add significant support to the hypothesis that annuli are accreted annually and

make possible the identification of annuli (Thompson et al. 1980a,

b; Jones 1980; Bennett et al. 1982; Turekian et al. 1982; Murawski

et al. 1982; Ropes et al. 1984). A large ocean quahog valve marked

in 1978 and recovered in 1983 is shown in Figures 3a and b. The

black periostracum has been peeled away in the marked area to

reveal the lack of discernible growth after the clam had been marked

(measurement indicated growth of only 0.7 rom). External rings

were not evident in the periostracal layer or annuli beneath it. In

contrast, a small ocean quahog valve marked and recaptured during the same years displayed visible external rings in the periostracal

layer and substantial growth (14.4 rom) after marking (Fig. 4a).

A photomicrograph of the acetate peel produced by our method

ofsectioning, embedding, polishing, and etching the ventral valve

margin of the large specimen shows an indentation from the mark-
b

"

c .

•• f

,. . ,.

100J.lm

t:

" .. .

j

Figure 3-a) A IlO-mm shell length ocean quahog, Arctica islandica, marked in 1978 and recaptured in 1983. b) Enlargement

of the paired parallel notch marks made at the ventral valve margin. Note that growth (estimated to be 0.7 mm) after notching

is barely visible. A millimeter scale was photographed with the valve. c) Replicate peel photomicrograph of the sectioned ventral margin showing the annulus formed soon after marking (arrow) and four annuli formed thereafter. A metric scale is included.

ing operation, the annulus formed soon after it was marked, and

four annuli thereafter (Fig. 3a). This clam and the small individual

were captured before the annuli for 1983 had formed. Annuli appear as dark wavy lines at the valve edge, but become more condensed thin lines back into the valve, conditions typical for large,

old clams. The annuli were identified as prismatic microstructures

in Scanning Electron Microscope (SEM) examinations (Ropes et

al. 1984). Growth increments have a light granular appearance under

a light microscope consistent with a predominantly homogenous

microstructure of ocean quahog shells. The very fine microstructural units are not evident under a light microscope.

The same features seen in the peel of the large ocean quahog occur

in the peel ofthe small individual, except that the growth increments

between annuli are more extensive and the annuli are typically nonwavy condensed lines (Fig. 4c). A peel of the hinge tooth shows

the same pattern of condensed annuli and growth increments for

the small individual (Fig. 4b).

SUMMARY _

Despite procedural modifications, the production of acetate peels

remains labor-intensive and time-consuming. It is the only known

method of producing accurate age data for large ocean quahogs,

and selected samples have provided significant information on the

age/growth phenomena of the ocean quahog. Arctica has been

characterized as a slow growing, long-lived bivalve [a 225-yearold individual may be the oldest recorded bivalve (Ropes and

Murawski 1983)] and it is not uncommon to capture individuals

100 years old. The frequent occurrence of old individuals complicates application of the method on a population-wide basis.

4
a

1978

c

Figure 4-a) A 62-mm shell length ocean quahog, Aretiea islandka, marked in 1978 and recaptured in 1983. Paired parallel notches clearly delimit growth (estimated

to be 14.4 mm) after marking. b) Eleven annuli are shown in the photomicrograph of the clam's hinge tooth. These corresponded to the same number of annuli found

in the valve. c) Replicate peel photomicrograph of the sectioned ventral valve margin showing an annulus that had formed soon after marking and four annuli formed

thereafter. Each annnlus is identified by the year of its formation. A millimeter scale applies to peel replicate photomicrographs b and c.

CITATIONS _

BENNETT, J. T., K. K. TUREKIAN, W. J. SHAUL, and J. W. ROPES.

1982. Using natural radionuclides to measure shell growth rates and ages of the

bivalves Are/ica is/andica (Linne) and Panope generosa Gould. J. Shellfish

Res. 2:88-89.

CARRIKER, M. R.

J979. Ultrastructural effect of cleaning molluscan shell with sodium hypochlorite

(Clorox). Nautilus 93:47-50.

FEDER, H. M., and A. J. PAUL.

1974. Age, growth, and size-weight relationships of the soft-shell clam, Mya

arenaria, in Prince William Sound, Alaska. Proc. Nat!. Shellfish. Assoc.

64:45-52.

JONES, D. S.

1980. Annual cycle ofshell growth increment formation in two continental shelf

bivalves and its paleoecologic significance. Paleobiology 6:331-340.

KENNISH, M. J., R. A. LUTZ, and D. C. RHOADS.

1980. Appendix I. Preparation and examination ofskeletal materials for growth

studies. Pan A: Molluscs. I. Preparation of acetate peels and fracture sections

for observation of growth patterns within the bivalve shell. In Rhoads, D. C.,

and R. A. Lutz (eds.), Skeletal growth of aquatic organisms, p. 597-601. Plenum

Press, N.Y.

KUMMEL, B., and D. RAUP (editors).

1965. Handbook of paleontological techniques. W. H. Freeman, San Francisco,

852 p.

MERRILL, A. S., J. A. POSGAY, and F. E. NICHY.

1966. Annual marks on the shell and ligament of the sea scallop, P/aeopee/en

magel/anieus. Fish. Bull., U.S. 65:299-311.

MURAWSKI, S. A., J. W. ROPES, and F. M. SERCHUK.

1982. Growth of the ocean quahog, Are/iea is/andiea, in the Middle Atlantic

Bight. Fish. Bull., U.S. 80:21-34.

5

ROPES, J. W., and L. O'BRIEN.

1979. A uoique method of aging surf clams. Bull. Am. Malaco!. Union Inc.,

p. 58-61.

ROPES, J. W., and S. A. MURAWSKI.

1983. Maximum shell length and longevity in ocean quahogs, Arc/ica is/andiea

Linne. ICES/C.M. 1983/K:32, Shellfish Comm., 8 p.

ROPES, J. W., D. S. JONES, S. A. MURAWSKI, F. M. SERCHUK, and A.

JEARLD, Jr.

1984. Documentation of annual growth lines in ocean quahogs, Aretiea is/andica Linne. Fish. Bull., U.S. 82:1-19.

STEVENSON, J. A., and L. M. DICKIE.

1954. Annual growth rings and rate of growth of the giant scallop, P/acopecten

magel/anieus (Gmelin), in the Digby area of the Bay of Fundy. J. Fish. Res.

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