CHAPTER XXVII: THE MUSSELS AND ROCK- 

 EATERS 



Family Mytilid^e 



Shell equivalve, elongated or oval, beaks anterior ; hinge 

 toothless ; ligament long, internal ; shell lining pearly ; periostra- 

 cum thick, dark, often hairy. Mantle open except between 

 siphonal openings; four gills, elongated, leaf-like, attached to the 

 mantle at their dorsal margins ; foot cylindrical, spinning byssus ; 

 adductor muscles two, unequal. 



A large family with abundant representation on all shores 

 where they hang in masses on piers of wharfmg, and cover sub- 

 merged driftwood if it is lodged near the level of low water. 

 Some are burrowers ; some spin nests out of bits of shells and 

 sand held together by byssal threads. Some hide in the burrows 

 of rock borers, or excavate soft rock to make their own retreats. 

 They are economically important as edible shell fish and as bait 

 for long-line fishing. The principal genera are represente4 in 

 this country. 



Genus MYTILUS, Linn. 



Shell obliquely and narrowly fan-shaped, rounded behind, 

 with terminal, pointed beaks in front. Mantle margins plain, 

 projecting sHghtly behind; incurrent tube of siphon fringed ; palpi 

 long, pointed ; gills sub-equal ; flesh white ; byssal gland in 

 "heel" of the small foot ; byssus strong, coarse. A world-wide, 

 gregarious genus of sixty-five species. 



The Edible Mussel (M. edulis, Linn.) native to the tem- 

 perate shores of Europe, has proved a hardy immigrant to both 

 our coasts. Acres of them are exposed to low tide on mud flats 

 extending far up the estuaries of rivers that flow into the ocean. 

 Again, we find them attached in masses to the rocks of exposed 

 coasts, where the bottom is pebbly, and the water clear. A 

 favourite station is the underpinning of wharves, in water be- 

 fouled by contact with trafficking towns. Every outgoing tide 



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