Astarte borealis

A. borealis are found in the boreal areas of Arctic, Pacific, and Atlantic Oceans.^[3] Currently studies have collected samples from the Baltic Sea,^[4] White Sea of Russia^[5] and Northern Alaska.^[6] Populations are widespread and found in the Pacific Ocean from the Sea of Okhotsk to the Aleutian Islands, in the Arctic waters of Russia from the Barents Sea to the Chukchi Sea, and in the Atlantic Ocean from Newfoundland to Greenland and Iceland, and in Europe in both the North and Baltic Seas.^[5] A. borealis is essentially a shallow water species (0–300m). Due to low salinities A. borealis submerges the brackish waters and lives in deeper regions with higher salinity. The optimal salinity range lies between 14 and 30 psu. It can survive in salinities between 10 and 15 psu with its minimum tolerance at 6–8 psu.^[7]

The exterior characteristics of genus Astarte include the periostracum, ribs and overall shell shape. The genus has a shell outline that is primarily trigonal with variations that are elliptical, ovate or subquadrate. The genus is equivalve and the length is equal to or greater than the height. The sculpture of the genus consists of commarginal ribs, most of which are equally spaced and vary from fine to broad-sized ribs; A. esquimalti has irregular, wavy ribs. The umbones are mostly broad and inflated; a few species have pointed umbones that are generally just dorsal of the midline. The umbones are prone to erosion in older specimens, which causes a difference in the appearance between juvenile and adult individuals. The periostracum is thick to this and varies from shiny to silky to dull across the genus. It is generally a yellow to black to reddish-brown and adherent.  

The shell shape of Astarte borealis is ovate to subquadrate to sub trigonal with umbones subcentral, just dorsal of midline, and often eroded in older individuals. The sculpture consists of fine, commarginal ribs or striae, and may possibly have raised ribs around the first 6–8 mm of the umbones. The periostracum is fibrous and adherent, thick, and yellow to black. Astarte borealis has a strong hinge as well as strong ligament attached to two prominent nymphs. The left valve has three teeth, two are larger cardinal teeth and the third is very small and inconspicuous. The right valve has right valve has two teeth, the anterior much larger and broader than the posterior tooth. The adductor muscle scar is deeply impressed, and the anterior pedal retractor scar is prominent. No pallial sinus and the pallial line is narrow and sometimes faint. The interior margin is smooth and unregulated in most, in a very few they may be some very light crenulations present. Almost always, the lack of crenulations will differentiate A. borealis form another Astarte species.^[6]

In terms of abundance and biomass, A. arctica and A. borealis have the highest values and are visually fairly similar in the color spectrum of the periostracum, irrespective of their size and age variability. The shell of these species is rather thick and heavy, tissue weight accounts for only 11–16% of total weight, which generally corresponds to values reported for A. arctica and A. borealis in other parts of their geographical ranges. Thus, the tissue weight of A. borealis from the Baltic Sea is on an average 14.5% of the total weight, i.e., the shell is fairly massive and solid. This reflects the adaptation of these mollusks for life on hard gravelly pebbly bottoms and, unlike many other epi- and infaunal organisms having a thin shell, helps them survive under the mechanical action of the bottom substrate, as well as trawls, dredges, etc. in conditions of active demersal fishery.^[8]