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CHAPTER XX 



LIMNORIA AND ITS ALLIES: THE CRUSTACEAN BORERS 



The foregoing chapters have dealt altogether with the wood-boring mollusks, 

 which, in view of their remarkable adaptation to boring life and the extraordinary 

 rapidity of their destructive work, have properly received first consideration. This 

 should not be interpreted, however, as minimizing the importance of a second group 

 of marine wood-boring animals, referred to collectively as the crustacean borers. 

 This group of organisms, while less immediately and spectacularly destructive than 

 certain of the wood-boring mollusks, nevertheless take a continuous toll of wharf 

 piling and other marine woodwork which in the aggregate is tremendous. 



The more important of them occur in waters of a salt content approaching that 

 of the open sea; but some invade brackish waters, and even extend their activities 

 some distance up from the mouths of fresh water streams. 



The crustacean borers belong to two orders, Isopoda and Amphipoda. These 

 may be distinguished in general by the fact that the isopods are more or less compressed 

 dorso-ventrally, like the terrestrial wood-lice or sow-bugs found commonly in damp 

 places, while the amphipods are laterally compressed, like the sand-fleas observed 

 along the ocean beach. 



The isopod borers constitute the more important group, including the well 

 known genera Limnoria and Sphaeroma. The amphipod borers include two species of 

 Chelura. These organisms will be discussed in the order named. 



Genus Limxoria 



This well known and widely distributed genus embraces six species, of which 

 the most familiar and most important economically is Limnoria lignorum. This 

 species is of almost world-wide occurrence, while the others are apparently limited 

 in their distribution to portions of the Pacific and adjacent seas. The following account 

 refers particularly to L. lignorum, with some reference to other species insofar as their 

 distribution and habits are at present known. 



Historical 



Attention was called to the destructive habits of Limnoria, or the "gribble," by 

 the renowned English engineer, Robert Ste\'enson, who found it destroying timbers 

 used in the construction of the Bell Rock lighthouse, off the coast of Scotland, during 

 the years 1807-18U. The animal was described as Limnoria terebrans by Leach, in 

 1814, on the basis of specimens sent to him by Stevenson. It had, however, been 

 previously described by Rathke in 1799 and included by him in the genua Cymothoa 

 as C. lignorum. The present and correct nomenclature was established in 1857 by 

 White, as Litnnoria lignorum (Rathke); he included it in the family Asellidae. In 

 1880 Harger established the separate family Limnoriidae, in which the genus Limnoria 

 is now placed. 



Moll (1915) points out that although Limnoria was not described until 1799, it 

 was doubtless active long before that time. Moll states: "Dampier, the great French 

 mariner, writes in 1723 that his ship, besides being attacked by the shipworm, also 

 was attacked by small, white animals like sheep-lice or small locusts. Scllius (1733) 

 figures these animals and calls them 'Springertje.' The 'Deicligrajen von Drechterland' 



