1671 



Shuster, Carl N., Jr. 1969. 



A three-ply representation of the major organ systems of a quahaug. Atl. 

 States Mar. Fish. Comm. , Marine Resources of the Atlantic Coast, Suppl . to 

 Leaflet 14 (Miller et al.- Hard Clam), 8 p. 



Relative positions of major organ systems of hard clam are printed on heavy 

 stock, back to back, so that three sections can be cut out, folded, arranged 

 in sequence, and stapled in the hinge area. The result is a sequence of 

 visualisations from exterior to interior of the clam, with all major 

 structures labelled. Drawings are of professional caliber. This is a useful 

 guide to hard clam morphology. - J.L.M. 



1672 



Shuster, Carl N. , Jr. 1971. 



The hard clam and soft clam of the western Atlantic coast. Ann. Repts . (1970) 

 Am. Malacol. Union: 13-15. 



Mercenaria mercenaria and M. campechiensis were important foods and artifacts 

 to Indians. Quahaug valves were broken and the pieces ground into cylindrical 

 beads. This strung wampum or shell-money had different values. Dark, purple- 

 colored beads were worth twice as much as white beads. Sections of crenulate 

 shell margin were pressed against moist clay to form designs on pottery. 

 Hard-clam production averaged 14.3 million lbs of meats/yr in the period 

 1959-1968. New York was first with 5.4 million lbs, followed in order by N.J., 

 R.I., Va., and Mass. Other states produced minor amounts. Intertidal 

 populations provided popular sport fisheries. Hand gears for hard clam include 

 hoes, rakes, bullrakes, and tongs. Power dredging is more efficient. 

 (Abstracter's note: it is not mentioned that in most areas power dredging is 

 permitted only on leased grounds.) Hard and soft clams sometimes coexist, but 

 not with each in abundance. Their ecologies obviously are somewhat different. 

 Soft clam ranges from the Canadian maritimes to N.C., northern hard clam 

 principally from Maine southward, and southern quahaug, which has commercial 

 offshore populations, from N.J. to Gulf of Mexico. Spawning is in early summer 

 when critical temp thresholds are reached, and as temp drops in fall a second 

 spawning may occur. The 2 Mercenaria species easily hybridize in the 

 laboratory. Spawning can be induced easily in conditioned quahaugs. Eggs of 

 hard clam have a gelatinous envelope. Fertilization is in the surrounding 

 water. Within 2 hrs, depending on temp, the 2-celled stage is reached. Food, 

 turbidity and salinity also affect rate of development. In about 12 hrs at 

 room temp a microscopic ciliated trochophore larva hatches. Soon shell 

 secretion begins and a straight-hinged, shelled larva is formed. As the 

 veliger enlarges, the shell changes shape and an umboned larval stage is 

 reached. The next stage is transitional, alternatively swimming or creeping 

 over the substrate. Metamorphosis is most common at 200-215 y shell length, 

 the velum is lost and the byssus gland becomes active. Byssus production 

 stops when the young clam is about 9 mm long. The juvenile mantle secretes 

 shell material over its entire surface, forming a laminated structure in 

 which most deposition is at the shell edges. A prominent growth ring on the 

 surface of the shell is associated internally with a prominent layer of 

 translucent material in cross-section, which marks a time of abrupt cessation 

 of shell growth. This can be a hibernation mark, or a record of a shorter 

 term disturbance such as a heavy storm. The oxygen-isotope method allows 

 determination of water temp at the time shell material was deposited. 

 Clams, especially young, are active burrowers. Shell, water jets, and 

 synergistic-antagonistic relations between hinge, muscles and hemocoel all 

 take part in burrowing. A special mucus-secreting region of the mantle 

 allows hard clam to expel mud, even when out of water. Largest clams 

 reported were: northern quahaug 6 1/8 in long, 2.5 lbs live weight; southern 

 species 6 5/8 in and 6.5 lbs. Mercenaria occasionally has asymmetrical 

 shell anomalies or a bifurcated siphon. - J.L.M. 



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