309 



Harger states in 1880 that the organism was distributed generally along the Atlantic 

 coast from the Gulf of St. Lawrence to Florida. In 1874 Hewston found a species 

 of Limnoria in San Francisco Bay, which he pnnisionalK- called L. cahfornica. liut 

 which was undoubtedly L. lignorum. 



Other species of Limnoria have since been described. L. segnis was discovered 

 in New Zealand in 188,^ by Chilton; L. antarctica was described by Pfeffer (1887) in 

 Part 1 of the "Crustacea of South (leorgia." Stebbing in 1906 described L. pfefferi 

 from the atoll of Minikoi in the Pacific. Stebbing gives a summary of the characteris- 

 tics of the above species in his account of the Isopoda from the Maldive and Lacca- 

 dive Archipelagoes. L. japonica was described by Richardson in 1909, from the waters 

 south of Japan. The most recent species is L. andreivsi, described by Caiman from 

 Christmas Island in 1910, and lately reported by Miller (1924c) from Hawaii and 

 Samoa. All of the aliove are wood borers excepting the species pfefferi and antarctica, 

 which were found on kelp. 



It has been suggested that shipping may have been a factor in bringing about the 

 cosmopolitan distribution of L. lignorum, the method of transfer being ballast water 

 in the case of steel-hull ships, and infected bottoms in the case of wooden ones. Al- 

 though neither method has been established definitely as operative, it is conceivable 

 that, in the intake of some tons of ballast water by a ship King at a wharf, the piles 

 of which are infected, many small organisms of all kinds, including Limnoria and 

 other crustaceans, will be taken in. Rubbing and chafing of the ship against the wharf 

 may remo\e small fragments of wood which carry Limnoria, and these may then be 

 drawn in with the ballast water. Certainly the prevalence of this organism in maritime 

 countries generally indicates that shipping has, by one means or another, been a 

 considerable factor in its distribution. 



The Morphology of Limnori.\ 



The EXTERNAI, MORPHOLOc.Y of Limnoria has been well described by several 

 authors. Excellent figures of the external form and of the internal anatomy are to 

 be found in the paper by Hoek (1893). 



The animal is a rather generalized isopod. The body is sub-cylindrical and elon- 

 gated (fig. 125). The eyes are small and are sessile. Both pairs of antennae are short. 

 As is the rule in this group, the first thoracic somite is indistinguishably fused with the 

 head, and the corresponding pair of appendages are modified to serve as mouth parts 

 (maxillipeds, see below). The remaining seven thoracic segments are free as are the 

 first five abdominal ones. The sixth abdominal somite is tused with the telson, and 

 the last pair of appendages, the uropods, seem, therefore, to arise from the latter. 



Each free thoracic somite bears a pair of walking legs. The first five abdominal 

 somites each bear a pair of thin, plate-like appendages, pleopods, that serve both for 

 swimming and for respiration. The last abdominal somite bears the uropods as 

 mentioned above. 



As there is no doubt that Limnoria accomplishes its boring by means of the 

 ■mouth parts, it is of interest to mention briefly their chief characteristics. 



The mouth parts consist of the following paired structures, from anterior to 

 posterior: the mandibles, the first maxillae, the second maxillae, and the maxillipeds. 

 These mouth parts, being mo\-able, are to be distinguished from the upper and lower 

 lips and the mctcpistomum, a hard reinforcing chitinous plate abo\-e the upper lip. 

 The general arrangement of the mouth parts is shown in figure 126. The mandibles, 

 maxillipeds, and first and second maxillae are shown in figures 127 and 128. 



