Manila Littleneck Clam. Size and Shape: Up to 2.5 inches. Oblong similar to Native Littlenecks but more oval . S.: Concentric rings with radiating line ridges..Clams belong to the group of animalsed bivalves, which includes clams, mussels, oysters, and s.ops. The soft body parts of these animals are enclosed . - A number of clam sfeatures are used to identify clams. Shape and size are usually coupled with exterior and interior design of s.s to positively identfy clams. Know what you 're digging before your shovel starts working! See information about identifying clams by their show.. - To tell the horse and softsclams apart, hold the clams on their ends and see whether the outlines of both s.s are the same. If they are, then it is a horse clam Figure 3 - right . If one sseems to overlap onto the other Figure 3 - left , then it is an eastern softsclam..