Tellina agilis was found at almost all stations sampled in the New 

 York Bight apex. Although it tolerated a wide range of sediment 

 types, it was most characteristic of fine or medium grain, low 

 organic sands. Tellina agilis was the second most abundant bivalve 

 in our samples, following Nucula proximo (Fig. 22; Table 1). 



FEEDING ECOLOGY: Tellin clams have two long, slender 

 siphons, which can be extended several times the length of the 

 shell, permitting the clams to live well below the surface of the 

 sand, while deposit feeding on the sediment surface. The large foot 

 is suitable for rapid and deep burrowing and the clams travel exten- 

 sively under the sand, both vertically and horizontally (Abbott 

 1968). Stomach analyses show that T. agilis feeds largely on 

 diatoms and detritus (Sanders et al. 1962; Levinton 1972; Levinton 

 and Bambach 1 975 ) . Kinner et al . (1 974) stated that they may occa- 

 sionally be suspension feeders. This dual feeding mechanism may 

 explain the occurrence of T. agilis in a wide range of sediment 

 types. 



It has been found that the movement of siphons of Tellina spp. 

 may attract visual predators such as the commercially important 

 winter flounder, Pseudopleuronectes americanus (Gilbert 1970; 

 Gilbert and Suchow 1977). Edwards et al. ( 1970) have shown that 

 in Scotland, small flounder. Pleuronectes platessa. obtain a large 

 part of their food by preying on siphons of Tellina tenuis da Costa, 

 which can later be regenerated. However, more studies are needed 

 to determine the importance of T. agilis siphons in the diet of young 

 winter flounder. 



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Figure 22.— Distribution and abundance of Tellina agilis in the New York Bight 



apex. 



REPRODUCTION AND GROWTH: Sexes are separate and fer- 

 tilization is external (Gosner 1971). The larvae of T. agilis are 

 planktotrophic with a long pelagic development. Time to maturity 

 is unknown (Sullivan 1948; Boss 1966). 



Ensis directus Conrad, 1843 



DESCRIPTION: Atlantic jackknife clam; up to 25 cm in length; 

 six times as long as high, moderately curved with sharp edges. 

 Shell white, covered with a thin, varnish-like brownish-green 

 periostracum (Abbott 1974). In its undisturbed state, Ensis directus 

 occupies a vertical position in its burrow with an inch or two of 

 shell exposed. When disturbed, it burrows rapidly to safety propel- 

 ling itself by releasing jets of water around the base of the foot; it is 

 also a capable swimmer (Drew 1907; Abbott 1968). 



DISTRIBUTION: Labrador to South Carolina, Florida (Abbott 

 1974). 



HABITAT: Common on sand flats of New England, but subtidal 

 beds in sandy mud at depths of 3-9 m are not uncommon (Abbott 

 1974). In Long Island Sound, Franz (1976) found E. directus to be 

 characteristic of the medium sand assemblage. In Virginia, it is an 

 intertidal and subtidal form found in waters above 20% salinity 

 (Wass 1965). Under experimental conditions, however, Chanley 

 (1969) found that E. directus could be acclimatized to survive at 

 7.5-28% . however, a rapid salinity change of 15%„ within this 

 range was lethal. 



In the New York Bight apex, E. directus occurred in low abun- 

 dance, 10/m : , at each of six stations, in depths <28 m. It was 

 present, alniost exclusively, in low organic medium and fine sands 

 (Fig. 23; Table 1). 



FEEDING ECOLOGY: E. directus is a suspension feeder (Wig- 

 ley 1968). It is a food item for man as well as for invertebrates. 

 McDermott (1976) stated that Cerebratuhis lacteus (a nemertean 

 worm) feeds on E. directus by entering its burrow from below and 

 engulfing the anterior end of the bivalve. This predation was 

 observed from New Jersey to North Carolina. Polinices duplicatus 

 (a moon snail) captures E. directus by approaching it below the sur- 

 face of the substratum and irritating its lower portion so that the 

 clam retreats upward. The snail then coats the razor clam with an 

 envelope of slime which appears to have an anesthetic property. 

 Successful capture probably depends on the ability of the snail to 

 maintain contact with its prey until anesthesia has taken place 

 (Turner 1955). 



REPRODUCTION AND GROWTH: According to Williams 

 and Porter (1971), planktonic juvenile E. directus occur abun- 

 dantly from December to June in North Carolina. They exhibit long 

 pelagic development with time to maturity unknown (Turner 1953). 



ADDITIONAL INFORMATION: McCall (1977) characterized 

 E. directus as an "equilibrium" species, i.e.. it is present early in 

 colonization, but remains at low and constant abundance. Relative 

 to more opportunistic species, equilibrium species exhibit slow 

 development, few reproductions peryear. low recruitment, and low 

 death rate. 



Sailaand Pratt (1973) stated that although the razor clam is abun- 

 dant along the east coast, it has not been exploited commercially as 

 on the west coast. Scattered fisheries for local markets in Massa- 



16 



