M. T. Thorell on Argulus dactylopteri. 45 



XI. — On Argulus dactylopteri, a new Marine Argulid from the 

 West Indies, By T. Thorell*. 



As a supplement to my paper on the Crustacean family of the 

 Aryulid(B\y I submit the following description of a new species of 

 that family, which has been kindly communicated to me by 

 Professor S. Loven, together with the information that it was 

 found in the gill-cavity of a Dactylopterus volitans (Linn.) from 

 the West Indies. 



The number of Argulids which live exclusively in the sea 

 has hitherto been limited, as far as we know for certain, to 

 two species, viz. Argulus purpureus (Risso) and Argulus gigan- 

 teus, Lucas, both from the Mediterranean, of which, moreover, 

 only the first-named species is known with any completeness. 

 Consequently the discovery of a new marine Argulid is in itself 

 an occurrence of some interest — so much the more so, however, 

 since the West-Indian species, in such points as are most 

 essential systematically (i. e. the structure of the mouth and 

 legs), approaches the European A. purpureus, and forms with 

 it (and perhaps also A. giganteus) a natural group {Agenor, 

 Risso), reminding us, however, in the weaker development of 

 the head-shield, of the common Argulid-type exemplified by the 

 freshwater forms A. foliaceus (Linn.) and A. coregoni, Thor. 

 As is the case in A. purpureus, the swimming-feet lack the 

 " tassel " {flagellum) ; the mandibles are placed near the open- 

 ing of the mouth, and the "lip'' is open beneath. The inter- 

 mediate joint or '* patella,'' found on the second pair of maxilli- 

 peds in A. purpureus, is wanting in A. dactylopteri as in A. folia- 

 ceus and other species. This species is especially remarkable 

 for the great difference which exists between the sexes : in the 

 other known Argulids such difference is principally displayed in 

 the form of the posterior portion of the body or tail, and in a 

 very shght degree affects the head-shield ; in A. dactylopteri 

 this part also is of an entirely different form in the two sexes. 



The specimens which I have examined were twelve in num- 

 ber, and seem to have been about half the number actually 

 found on the fish. Thus more than twenty of these parasites 

 lived in the gill-cavity of this fish. Those examined are of very 

 different sizes, from 4 to 8 millimetres long; only three of them 



* Communicated Dec. 14, 1864. See * (Efvers. Kongl. Vetensk.-Akad, 

 Forhaudl.' Translated by Arthur W. E. O'Shaughnessy. 



t Thorell, * Om tvenne Europeiska Argulider ; jemte anmarkningar om 

 Argulidernas morfologi och systematiska sfallning, samt en ofversigt af de 

 for narvarande kanda arterna af denna familj ' (translated, from the * (Ef- 

 vers. af K. Vet.-Akad. Forhandl. 1864,' pp. 7-72, in Nos. 106, 106, & 108 

 of this Joiumal). 



