LARVAL AND POSTLARVAL DEVELOPMENT OF THE CORRUGATED JEWEL BOX CLAM CONGREGATA CONRAD (: )1

MICHAEL LABARBERA2 College of Agriculture, Cornell University, Ithaca, New York 14850

AND PAUL CHANLEY3 Virginia Institute of Marine Science, Gloucester Point, Virginia 23062

ABSTRACT The larvae of Conrad, a sessile, dimyarian tropical bivalve, were reared and described to facilitate their identification in plank- ton and bottom samples. The dimensions (in microns) were determined (L = length; H = height; D = depth). Straight hinge stage: L = 76-139; H = 62-128; D = 43-87; L - 15 = H ± 6; L - 50 = D ± 12. Straight hinge-line = 56-66. Umbo stage: L = 112-214; H = 95-203; D = 66-152. L - 3 = H ± 19. L - 52 = D ± 14. Umbo broadly rounded with ends bluntly pointed. Pediveligers: Length 177-214. Height subequal to or greater than length. Two teeth appear in right valve during late umbo stage. The liga- ment is external. Larvae first attach by byssus at a length of 200p. but are not permanently cemented until about 350".. long. Juveniles have adult shell characteristics at a length of 500p..

INTRODUCTION Chama congregata Conrad (Fig. 1) is a member of the superfamily Chamaceae, a small group of dimyarian clams composed of one family (the Chamidae), five genera, and 50 living species (Vokes, 1967). C. congregata is common from North Carolina to Florida and the West Indies, cemented by the more cupped left valve to the valves of other molluscs (Abbott, 1954) or coral. It is small (rarely over 25 mm), with low axial corrugations or short, flat spines on the upper or right valve. Frequently, this clam is camouflaged by other encrusting or fouling organisms, including juveniles of the same species, and by its own inconspicuous appearance. The morphology of the Chamidae has been extensively reviewed by Yonge (1967), but their larval development is unknown. The purpose of this report is to describe the larval and postlarval development of Chama

1 Contribution No. 422 from the Viriginia Institute of Marine Science. This project was financed in part by National Science Foundation Undergraduate Research Participation Grant GY 4382. o Present Address: Department of Zoology, Duke University, Durham. North Carolina 27706. "Present Address: Shelter Island Oyster Co., Greenport, New York 11944. 734 Bulletin of Marine Science [21(3 )

10 mm

FIGURE 1. Adults of Chama congregata: left, whole ; right, valves open, lower valve above. congregata in such terms as to facilitate their identification in plankton and bottom samples.

MATERIALS AND METHODS Individuals of C. congregata were collected from a coral head dredged from off southern North Carolina between 77"36' and 77°46'W and 33° 35' and 33°53'N. Because the left valve was cemented to the substrate, it was necessary to chip off fragments of the coral to remove the clams. In the process a few were broken. These were opened completely and found to be sexually mature and dioecious. Several fruitless attempts were made to induce the survivors to spawn by rapidly raising water temperatures from 17°_20° C to about 32° C and adding stripped sperm. Using an alter- 1971J LaBarbera & Chanley: Development of Chama congregata 735

FIGURE 2. Sperm of C. congregata: electron micrographs of spermatozoan head (actual dimensions 35M X 25M), native method, sperm were then removed from the males by puncturing the gonads and removing the gametes with a Pasteur pipette. Eggs were ob- tained by exposing the ovaries and washing out the eggs with a stream of filtered sea water. The eggs were subsequently kept in 100 cc of a 3 per cent solution of O.IN ammonium hydroxide for 20 minutes to break down the germinal vesicle (Loosanoff & Davis, 1963). In a previous experiment, the eggs were unfertilizable without such treatment. Sperm were then added and the suspension was diluted to approximately 15 liters in a polyethylene container, where development continued. Culture methods approximated those of Loosanoff & Davis (1963). The larvae were reared at 25°C in filtered sea water with a salinity of 28 %0-30 %0 and were fed unicellular algae (lsochrysis galbana). The water was changed three times weekly by siphoning the cultures through a stainless steel screen with a pore size of 35p. (diagonal 50p.). At the same time, actively swimming larvae were separated from those at or near the bottom. Larval concentrations were maintained at 5-lOjcc. The larvae were measured at 100x with a filar micrometer. Dimensions are given in microns in the Results section. The meanings of the abbreviations are as follows: L = length, the maximum anterior-poste- 736 Bulletin of Marine Science [21 (3)

MIDDLE PI ECE

TAIL

FIGURE 3. Living sperm (total length 54p.).

rior dimension; H = height, the maximum dorsal-ventral dimension; D = depth, the maximum right-left dimension.

RESULTS Gametes.-Mature, stripped eggs: Diameter 61.2-66.3, x = 62.9, including membrane; yolk coarse, membrane closely appressed. Sperm: cylindro- conical; head 3.5, including center piece; basal width 2.5; tail about 51 (Figs. 2, 3). Larval Dimensions (Fig. 4) .-Straight-hinge stage: L = 76-139; H = 62- 128; D = 43-87; L - 15 = H ± 6; L - 50 = D ± 12. Straight hinge-line 51- 1971] LaBarbera & Chanley: Development of Chama congregata 737

FIGURE 4. Dimensions of larvae of C. congregata. Height and depth coordi- nates run parallel to the length axis. Dots represent observed length-height or length-depth measurements. The lines representing probable maximum and mini- mum dimensions were fitted by eye. The three-dimensional figure in the center encompasses all possible length-height-depth combinations of the larvae of C. congregata. The graph is explained in greater detail in Chanley & Van Engel (1969). 738 Bulletin of Marine Science [21(3)

FIGURE 5. Veliger larvae of C. congregata (dimensions of larvae at right are given in microns, length first, height second): A, one-day-old straight-hinge stage; B, late straight-hinge stage; C, early umbo stage; D, umbo stage, larva at right margin with velum extended; E, late umbo (early pediveliger) stage; F, late pediveliger.

71 (usually 56-66), not increasing in length with larval growth. Linear regression equation: Hinge-line = 61 - 0.02L, r = -0.08. Umbo stage: L = 112-214; H = 95-203; D = 66-152; L - 3 = H ± 19; L - 52 = D ± 14. Height exceeding length in one-third of larger larvae and equaling length in one-tenth. Pediveliger stage: Functional foot first appearing at L = 177. Largest larvae with functional velum at L = 214. The linear regression equations are: for height, H = -29 + 1.51L, r = 0.99; for depth, D = -14 + 0.74L, r = 0.96. Larval Shape (Fig. 5) .-Straight-hinge stage: Larvae D-shaped, with slope of anterior shoulder more gradual than that of posterior. Anterior half of valves longer than posterior half. Ventral margin evenly rounded. 1971] LaBarbera & Chanley: Development of Chama congregata 739

•

•• t .. A • - B

c

FIGURE 6. Juveniles of C. congregata: A, straight line formed by hinge and dorsal margin apparent; B, byssal thread apparent at center right; C, tooth in right valve prominent, inequivalve form obvious (left valve uppermost).

Umbo stage: Broadly rounded umbo protruding beyond hinge line at at L = ca. 133. Straight hinge-line totally obscured when L = 145. Umbo increasingly conspicuous with larval growth (Fig. 5). Ends of larvae bluntly pointed, with anterior end longer and more pointed than posterior. Anterior and posterior shoulders nearly straight with anterior longer and sloping more gradually than posterior. Juveniles: All but dorsal valve margins flattened with dissoconch growth. 740 Bulletin of Marine Science [21 (3) 1971] LaBarbera & Chanley: Development of Chama congregata 741

STOMACH INTESTI NE DIGESTIVE GLAND ANUS ANTERIOR ADDUCTOR POSTERIOR ADDUCTOR

MANTLE VELAR RETRACTORS VELUM

INTESTINE

POSTERIOR ADDUCTOR

STATOCYST STOMACH

ANTERIOR ADDUCTOR

ANUS DIGESTIVE GLAND BYSSAL SPUR-----·' BYSSAL GLAND VELAR RETRACTORS FOOT VELUM MANTLE

I I I I I I I I I I o 50 100 MICRONS

FIGURE 8. Internal anatomy of larvae of C. congregata: top, late straight-hinge stage; bottom, pediveliger.

Growth initially more rapid along posterior end, but from ca. L = 240 through remaining developmental growth, more rapid at anterior end. Pos- terior slope with projecting, concentric lamellate flanges between hinge and valve margin along growth lines. Older juveniles with straight line formed by hinge and dorsal margin of valves superficially resembling dorsal margin of juvenile scallops. Growth of valve margins never extending dorsally beyond hinge-line (Fig. 6). After cementation, more rapid growth in left valve resulting in inequi- valve form characteristic of adults (Fig. 6). Valve growth faster on anterior end, especially along ventral margin, yielding large, generically characteristic umbo curved to right (attached position). The right valve developing lamellae and numerous very flat, broad spines. Juveniles with all adult shell characteristics by 500}.t. 742 Bulletin of Marine Science [21 (3) Hinge structure (Fig. 7).-Simple until late umbo stage, then two teeth developing in right valve, one central and one anterior. Long exterior liga- ment with expanded ends developing posteriorly. A red to red-brown color appearing in hinge area and umbo during late umbo stages. Soft parts (Fig. 8) .-Larva granular in appearance. Apical flagellum not observed in larvae beyond trochophore stage. In pediveligers, byssus gland and statocyst, with single statolith, embedded in base of foot (Fig. 8). Statocyst seen best with green or blue filters over light source. Larvae at 300 with siphons formed and animals actively pumping. Only excurrent siphon projecting beyond valve margins. Behavior.-At approximately 200ft, larvae began to crawl exclusively. At this size they attached by a single byssal thread that was frequently broken as they moved about. When larvae were provided with various attachment sites, they were found more frequently on algae-covered surfaces than on clean coral and least often on clean oyster shells. At approximately 350ft, larvae attached permanently to the substrate by a byssus and eventually became cemented by the anterior margin of the left valve.

DISCUSSION Larval development has not been described in any other species of Chamidae and consequently it is impossible to compare development of C. congregata with any closely related genera or species. Larvae of C. con- gregata are unusual in that, in later stages, larval height exceeds length. Al- though larval length and height are nearly equal in several species (Chanley & Andrews, unpublished manuscript), height is known to exceed length in only the Anomiidae, Ostreidae, and Teredinidae (Loosanoff et al., 1966). Compared with most bivalve larvae, those of C. congregata metamorphose at a relatively small size, 77ft to 214ft. However, they crawl about freely and do not permanently attach to the substrate until they have grown nearly 150ft and are about 350ft in length. Larval Ostreidae normally attach with- out undergoing an extensive free crawling stage, defined by Carriker (1961) as the "byssal plantigrade"; nonetheless, it may not be unusual for other bivalves, sessile as adults, to undergo a distinct "byssal plantigrade" stage after the velum is lost and prior to permanent attachment. Loosanoff (1961) observed this phenomenon in Anomia simplex, but apparently assumed it was abnormal. After this byssal plantigrade stage, juveniles of C. congregata cement themselves by their anterior ends with the anteroposterior axis initially perpendicular to the substrate. The horizontal position, characteristic of adults, is probably achieved by continued anteriorly directed growth of the shell. 1971] LaBarbera & Chanley: Development of Chama congregata 743

Adult Chamidae have a pair of statocysts (Yonge, 1967), but only one statocyst was observed in larvae. The possibility that two statocysts were in such close proximity that they appeared as one seems unlikely. More probably the adult condition develops later.

ACKNOWLEDGMENTS This work represents a cooperative effort of several organizations and individuals to whom the authors acknowledge their grateful indebtedness. Members of the Department of Microbiology, especially Mrs. Juanita Tutt and Miss Judy Ward, provided the necessary algal foods and assistance re- quired for successful culture of these larvae. Mrs. Jane S. Davis prepared the illustrations. The authors are especially grateful to Mr. James Sterling and the crew of the R/V DAN MOORE (research vessel of the North Carolina Department of Conservation and Development, Division of Commercial and Sports Fisheries) for collecting the many samples of living adult bivalves used as a brood stock.

SUMARJO

DESARROLLO LARVAL y POSTLARVAL DE Chama congregata CONRAD (BIVALVIA: CHAMIDAE) Las larvas de Chama congregata Conrad, un bivalvo tropical dimiariano, sesil, fueron criadas y descritas para facilitar su identificaci6n en muestras de plancton y del fondo. Se determinaron las dimensiones (en micrones) de los distintos estados (L = longitud; A = altura; P = profundidad). Estado de charnela recta: L = 76-139; A = 62-128; P = 43-87; L - 50 = P ± 12. Unea de la charnela recta = 56-66. Estado de umbo: L = 112-214; A = 95-203; P = 66-152; L - 3 = A ± 19; L - 52 = P ± 14. Umbo ampliamente redondeado con extremos obtusa- mente puntiagudos. Pedivelfgeras: Longitud 177-214. Altura subigual 0 mayor que ]a lon- gitud. Dos dientes aparecen en la valva derecha durante la ultima parte del estado de umbo. EI ligamento es externo. La primera fijaci6n de las larvas por medio de filamentos (byssus) ocurre cuando tienen una longitud de 2001-' pero no se adhieren permanente- mente hasta alcanzar alrededor de 3501-" Los juveniles presentan caracterfs- ticas de concha adulta al alcanzar una longitud de 5001-"

LITERATURE CITED ABBOTT, R. TUCKER 1954. American Seashells. Van Nostrand Co., Princeton, New Jersey, 542 pp. 744 Bulletin of Marine Science [21 (3)

CARRIKER, M. R. 1961. Interrelation of functional morphology, behavior, and autecology in early stages of the bivalve Mercenaria mercenaria. J. Elisha Mitchell scient. Soc., 17(2): 167-241. CHANLEY, P. AND W. A. VAN ENGEL 1969. A three-dimensional representation of measurement data. Veliger, 12(1): 78-83. LOOSANOFF, V. L. 1961. Partial metamorphosis in Anomia simplex. Science, 133(3470): 2070-2071. LOOSANOFF, V. L. AND H. C. DAVIS 1963. Rearing bivalve mollusks. Pp. 1-136 in Russell, F. S. (Ed.), Ad- vances in marine biology, I. Academic Press, New York and London, xiii + 410 pp. LOOSANOFF, V. L., H. C. DAVIS, AND P. E. CHANLEY 1966. Dimensions and shapes of larvae of some marine bivalve mollusks. Malacologia, 4(2): 351-435. VOKES, H. E. 1967. Genera of the Bivalvia: A systematic and bibliographic catalogue. Bull. Am. Paleont., 51 (232): 103-394. YONGE, C. M. 1967. Form, habit, and evolution in the Chamidae (Bivalvia) with reference to conditions in the (Hippuritacea). Philos. Trans. Roy. Soc., Ser. B (BioI. Sci.), 252(775): 49-105.