Composition and Distribution of Macrobenthic Invertebrate Fauna 



119 



0.49%) to very small (<0.01 g/m 2 ) as carbon content 

 increased to just under 2% (Table 28; Fig. 110). 



Frequency of occurrence in samples exhibited a trend 

 similar to that of biomass. Incidence was relatively low 

 (ranging from 2 to 12%) and diminished with increas- 

 ing carbon content (Table 30). 



Gastropoda — Gastropods formed a moderately com- 

 mon component of the New England benthos. They 

 were distributed throughout most of the studv area, but 

 because of their generally small size they accounted for 

 only a small proportion (1.2%) of the total benthic 

 biomass (Table 3). 



These mollusks varied enormously in size, from the 

 tiny Retusa and Alvania (approximately 2 mm in length ) 

 to large specimens of Neptunea, Colus, Busycon, and 

 Buccinum (ranging up to 13 cm or more). The majority 

 of specimens were between 2 and 30 mm. 



Shelled gastropods were predominant in our collec- 

 tions, although some shell-less groups (Nudibranchia 

 and Aplysiacea) were represented. Nudibranchs were 



abundant in a few localized shallow water habitats 

 but were generally uncommon to rare in the offshore 

 regions. 



Specimens in our samples were usually drab colored, 

 with various shades or combinations of white, gray, and 

 brown predominating. The shell-less groups contained 

 some of the more brightly colored forms. In these 

 groups light yellow, pink, orange, and rusty-red hues 

 were common on the dorsal body surface and in the 

 cerata and tentacles. 



Gastropods of different taxonomic groups obtain their 

 nourishment by a variety of methods. Feeding types 

 known to be represented in our collections were herbi- 

 vores, predacious and nonpredaceous carnivores, and 

 parasites. Carnivores and scavengers that feed heavily 

 on bivalve mollusks were the largest and most common 

 forms encountered. Parasitic species were rare. 



Gastropods occurred in 470 samples (44%). Their 

 density averaged 8/m 2 ; biomass averaged 2.2 g/m 2 

 (Table 5). 



