REPRODUCTION AND GROWTH: Sexes are separate, with 

 shells of males usually being smaller. Egg capsules, containing 

 about 50 eggs, are laid in rows on algae, shells, stones, or some- 

 times on the underside of moon snail "sand collar" egg masses 

 (Abbott 1968. 1974). In deeper waters of the continental shelf. N. 

 trivittatus spawn during May and June when seawater temperatures 

 are between 8° and 13°C. Intertidally. at Barnstable Harbor. 

 Mass. . spawning began in early May when seawater temperatures 

 rose rapidly from about 9° to 15°C (Scheltema and Scheltema 

 1965). Pechenik (1978) reported spawning in the laboratory to 

 occur at 7.4°C in December. Egg cases have been observed by 

 Scheltema and Scheltema (1965) in Barnstable Harbor in early 

 autumn. After about 1 wk at room temperature in the laboratory, 

 225 nm long free-swimming veliger larvae emerged from egg cap- 

 sules. Under favorable conditions of laboratory culture, metamor- 

 phosis into snails occurred at 22 d following emergence, with most 

 specimens between 0.9 and 1 . 1 mm in length at this stage. 



ADDITIONAL INFORMATION: Unlike many marine snails, 

 nassas are attracted toward light (Abbott 1968). 



Class Bivalvia 



Sucula proximo Say, 1822 



DESCRIPTION: Atlantic nut clam: 0.6 cm in length, obliquely 

 ovate, smooth. Color greenish gray with microscopic, embedded. 

 axial gray lines and prominent, irregular, brownish concentric rings 

 (Abbott 1974). 



DISTRIBUTION: Nova Scotia to Florida and Texas: Bermuda 

 (Abbott 1974). 



HABITAT: Common in mud and sand, 0.9-30 m (Abbott 1968, 

 1974). Menzel (1964) listed Nucula proximo as a subtidal mud 

 dweller occurring at salinities >25% in Florida. In Virginia, it 

 occurs in sand to silty sand, at salinities >20% (Wass 1965). In 

 samples taken near the mouth of Delaware Bay, N. proximo was 

 among the three most abundant species collected; there, it was a 

 member of a high silt-clay facies (>50% silt-clay) (Kinner et al. 

 1974). In the soft-bottom community of Buzzards Bay. Mass.. N. 

 proximo and Nephtys incisa dominated the fauna (Sanders 1958. 

 1960: Driscoll and Brandon 1973). 



In a prior apex study, Pearce ( 1 972) found N. proximo in greater 

 abundance around sludge deposits than in natural communities. In 

 the present study, N. proximo was again clearly most abundant in 

 high organic fine sands and silt, although it was present in all sedi- 

 ment types. It occurred in numbers between 10 and about 22.000/ 

 m : and was by far the most abundant bivalve collected (Fig. 16; 

 Table 1). 



FEEDING ECOLOGY: Nucula spp. are sporadically mobile, 

 normally lying at or just below the sediment surface feeding on the 

 sediment just beneath them by means of long appendages derived 

 from the palp. Only fine particles are moved along the groove to the 

 palps where they are passed by cilia to the mouth. Nucula spp. are 

 thus selective deposit feeders (Abbott 1968; McCall 1977). 



Nucula spp. are a source of food for several species of bottom- 

 feeding fish (Abbott 1968). 



opment. Time to maturity is unknown (Chanley 1969; Scheltema 

 1972). 



The size, shape, and coloration of this species vary according to 

 substrate and water temperature. Among the probable forms are: 

 truncula Dall, 1878; ovata Verrill and Bush. 1898: and annulata 

 Hampson. 1971 (Abbott 1974). 



Allen (1953, 1954) showed precise year-classes for five English 

 species of this genus. He postulated that the largest individual in his 

 samples was 12-20 yrold, depending on the species, and that the 

 yearly increment in length varied from 0.94 to 1.01 mm. regardless 

 of species or age. Blake and Jeffries (1971) grew N. proximo in 

 tanks. They estimated 2.0 mm/yr growth for the first size-class of 

 N. proximo and 1 .0 mm/yr for the second size-class. These esti- 

 mates are greater than Carey s (1962) estimate of 0.38 mm/yr for N. 

 proximo in Long Island Sound, but are similar to Aliens (1953. 

 1954) estimates for British species. 



ADDITIONAL INFORMATION: Levinton (1972) found .V. 

 proximo in Long Island Sound to be randomly distributed with a 

 tendency toward aggregation in some cases. Juveniles were distrib- 

 uted essentially the same as adults. It is argued that the lack of 

 defense mechanisms, the instability of the substrate, the small 

 "reach" of the feeding organ, and the lack of advantage of territori- 

 ality to a mobile deposit feeder, all contribute to the observed ran- 

 dom patterns of N. proximo. 



In experiments using a radioactive tracer, cadmium- 109 ( ltw Cd). 

 Jackim et al. (1977) showed that an increase in temperature or a 

 decrease in salinity increased the " w Cd uptake rate of N. proximo. 



NEW 

 JERSEY 



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I 40°20' 



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□ 



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m r 



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999 m 3 



El 



000 



-22.6)9 m- 



4010 



74 00 

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73°50' 



7340' 



I 



REPRODUCTION AND GROWTH: N. proximo exhibits no 

 egg protection; larvae are lecithotrophic with a short pelagic devel- 



Figure 16.— Distribution and abundance of Nucula proximo in the New York 

 Bight apex. 



11 



