Composition and Distribution of Macrobenthic Invertebrate Fauna 



217 



In the Southern New England Shelf subarea, density 

 was dominated by crustaceans (1385/m ), followed by 

 annelids (531/m 2 ), mollusks (244/m 2 ) and echino- 

 derms (123/m ) in tenns of density. Mollnsk biomass 

 (171 g/m 2 ) was dominant in this subarea followed by 

 significandy smaller amounts of echinoderm (36 g/m 2 ), 

 annelid (30 g/m ), and crustacean (17 g/m 2 ) biomass. 



The two continental slope subareas contained lower 

 densities and biomasses of all components than the 

 shelf subareas. The mean densities and biomass on 

 Georges Slope for the major taxa were as follows: Crus- 

 tacea, 138/m 2 and 0.6 g/m 2 ; Mollusca, 83/m 2 and 2.7 

 g/m 2 ; Annelida, 80/m 2 and 4.9 g/m 2 ; and Echinoder- 

 mata, 19/m 2 and 3.9 g/m 2 . Southern New England 

 Slope values were Annelida, 149/m 2 and 4.3 g/m 2 ; 

 Mollusca, 58/mr and 1.2 g/m 2 ; Arthropoda. 22/m 2 

 and 0.1 g/m 2 ; Echinodermata, 19/m 2 and 10 g/m 2 . 



Selected Genera and Species — This section deals with 

 the geographic distribution of 24 selected genera and 

 species of macrobenthic invertebrates. These particu- 

 lar forms were selected because of their common oc- 

 currence, regional ubiquity, or distinctive distribution. 

 Figures 244 to 249 depict the distributions of the se- 

 lected forms. 



Phylum Annelida 



Aphrodita hastata (Moore) (Fig. 244). Commonly 

 known as the sea mouse, this polychaete bristle worm of 

 the family Aphroditidae may attain lengths up to 150 

 mm (6 inch); smaller individuals are often found in 

 haddock, cod and red hake stomachs. It commonly 

 inhabits mud bottoms, or mixed bottoms with a high 

 mud content. 



Scalibregnia inflatum (Rathke) (Fig. 244). This me- 

 dium-sized (1-5 cm) polychaete is a member of the 

 family Scalibregmidae. An important food of many de- 

 mersal fish, this species inhabits silty sand substrates. 



Sternaspis scutata (Renier) (Fig. 244). This moder- 

 ately small (1 cm), burrowing polychaete is stout in 

 appearance and is a member of the family Stei naspidae; 

 it is found in the diet of winter flounder. It commonly 

 inhabits siltv sediments. 



Phylum Mollusca 



Arctica islandica (Linnaeus) (Fig. 244). This rather 

 large (18-15 cm) commercially harvested bivalve, known 

 as the ocean quahog, mahogany quahog, or black clam, 

 belongs to the family Arcticidae. It is a very slow-grow- 

 ing species that occurs very abundantly in some locali- 

 ties on the continental shelf. Small to medium-sized 

 individuals are preyed upon by cod and several species 

 of starfish. It usually inhabits muddy sand bottoms. 



Astarte undata Gould (Fig. 245), the common wavy 

 astarte of the family Astartidae, is a medium-sized (2.5- 



3.8 cm) bivalve. In the New England region, it is most 

 prevalent at mid-shelf depths (50-99 m) in sand and till 

 substrates. Although juvenile specimens are occasion- 

 ally found in fish stomachs, it is not a major prey item of 

 demersal fishes. 



Cerastoderma pinnulatum (Conrad) (Fig. 245), the 

 northern dwarf cockle, is a common, moderately small 

 (1 cm) bivalve belonging to the family Cardiidae. This 

 species is infrequently found in fish stomachs. It prefers 

 sandy substrates but does occupy, in lower abundance, 

 other types of sediments. 



Cyclocardia borealis (Conrad) (Fig. 245), the northern 

 cyclocardia, is a medium-sized (3-5 cm) bivalve of the 

 family Carditidae. Broadly distributed throughout the 

 region, it prefers sand and till substrates but does occur in 

 other sediments as well. It is not common in fish diets. 



Modiolus modiolus (Linnaeus) (Fig. 245), the north- 

 ern horse mussel, is the largest (5-15 cm) and most 

 common mussel of the offshore New England region; it 

 is a member of the family Mytilidae. It is found on the 

 periphery of the Gulf of Maine and on Georges Bank, 

 and extends onto the Southern New England Shelf. It 

 prefers sand and sand-shell substrates. 



Placopecten magellanicus (Gmelin) (Fig. 246), the sea 

 scallop, is one of the most valuable commercial shell- 

 fish resources of the U.S. East Coast, especially in the 

 New England region. It is a large bivalve (12-20 cm) of 

 the family Pectinidae, found most abundantly on coarse 

 sandy bottoms. In addition to harvest by man, juveniles 

 of this species are found in the diets of some demersal 

 fishes, principally haddock, and ocean pout. 



Buccinumspp. (Fig. 246) is represented in our samples 

 by four species in the family Buccinidae. The species 

 represented are B. elatius, B. gouldi, B. hydrophanum, 

 and B. undatum. Among the four species, the moder- 

 ately large (5-10 cm) B. undatum, the waved whelk, is 

 overwhelmingly the most common form. They are typi- 

 cally found at mid- to lower-shelf depths in sand and 

 coarser grained sediments. 



Neptunea decemcostata (Say) (Fig. 246), the wrinkled 

 whelk, is a moderately large (7-11 cm) gastropod be- 

 longing to the family Buccinidae. This species typically 

 inhabits hard bottoms ranging from coarse sand to 

 gravels at mid- to lower-shelf depths. 



Phylum Arthropoda 



Ampelisca agassizi (Judd) (Fig. 24(5) , this gammaridean 

 amphipod of the family Ampehscidae is a medium- 

 sized (4-7 mm) tube dweller. It is the most abundant 

 and common species of amphipod in the southwestern 

 half of the study area; in some localities it is exceptionally 

 abundant. It prefers a sandy substratum. This species is a 

 very common prey in the diet of many demersal fish. 



Leptocheirus pinguis (Stimpson) (Fig. 247), a species 

 of gammaridean amphipod, family Aoridae, is a moder- 



