Chit/fox. — Dixpcr-'^dl of Mariiu Cnistacea hij Metiiix of Sfii/is. 13' 



Akt. W]\. XoIc i>ti Ifii' Dispersal <ij M<tnnr (Vustarca, />// Means of 



Shi/ps. 



By CuAKi.E.s Chilton. M.A.. M.B., D.8e.. F.L.8.. Professor of Biology. 

 Canterbury College. University of New Zealand. 



[Read before the Philosophicdl histiliite of Cdiiti rhurii, 7th Deretiiber, 1910.\ 



It has several times been suggested that some of the marine Crustacea may 

 be unconsciously dispersed by man, owing to their becoming attached oi' 

 temporarily adhering to the hulls of ships. So far as I am aware, however, 

 few definite facts of this means of dispersal have been recorded. 



Mr. Stebbing (1888. p. 1135), in recording a specimen of Podocerus 

 jalcatus (Montagu) from Kerguelen Island, remarked, '" There is the possi- 

 bility, as I have elsewhere suggested, that these creatures may have 

 travelled out from our own waters along with the vessel to the southern 

 latitude at which thej'^ were captured."' This species, however, which 

 Stebbing gives in his "Das Tierreich Amphipoda" (1906, p. 654) imder the 

 name " Jassa pulchella Leach," proves to be very widely distributed both 

 in northern and in southern seas, and may have been dispersed, as I have 

 pointed out (1909, p. 647), owing to its habit of attaching itself temporarily 

 to the carapace of Jasus edwardsii and other large Crustacea ; and, though 

 it is possible it may also be distributed by attaching itself to ships in the 

 same way, this explanation seems hardly necessary for the particular case 

 Mr. Stebbing was then considering. 



In his " History of Crustacea " Mr. Stebbing gives a. more certain 

 example of this means of dispersal. He says (1893, p. 98), " In the winter 

 of 1873 an iron vessel entered the port of Marseilles. It had come from 

 Pondichery by way of the Cape of Good Hope, having had a long and stormy 

 voyage in the most rigorous season of the year. To the iron plates of this 

 ship had become attached a little forest of algae and barnacles, and living 

 among these were a numbe]- of higher Crustacea of exotic origin. Two 

 of the specimens were found by Professor Catta to belong to a new species, 

 which in 1876 he named Pachygrapsus advena : one was a Nautilograpsus 

 (or Planes) minutus, a species scarcely ever found in the Mediterranean ; 

 the remainder belong to two species, which M. Catta speaks of as Plagusia 

 squamosa and Plagusia tonientosa." Mr. Stebbing points out that the 

 latter species should be called Plagusia chabrus (Linn.), and the foi-mer 

 Plagusia depressa (Fabricius). The last-mentioned species was the most 

 abundant, being present in hundreds, though, as Mr. Stebbing points out. 

 being an Atlantic species it might not have had to come far. There seems 

 no doubt that the species mentioned had been brought from other places 

 into the Mediterranean by their becoming attached to the hull of this ship. 

 Dr. Alcock (1900. p. 437) has since pointed out that the Plagusiae resemble 

 Varuna in being able to make themselves at home on drift timber in the 

 open sea, and that the wide range of some of the species can be thus 

 accounted for. He states, however, that the two species found in the 

 Mediterranean may very probably have been carried there by ships, and 

 adds that on the " Investigator " Plagusiae could always be seen adhering 

 to the ship's sides near the water-line. 



We have another example of this methftd of dispersal in the case of the 

 common Eurdpea)i shore-crab Careinns nfomas. Dr. Alcock says (1899, 



