86 M. L. Plate on Ectoparasitic Rotatoria 



XII. — On some Ectoparasitic Rotatoria of the Bay of 

 Naples. By LuDWiG Plate *. 



[Plate VI.] 



There are referred to tlie Rotatoria certain forms which 

 depart widely from the ordinary type of this class and which 

 have this in common in their mode of life, that they live as 

 ectoparasites upon the marine Phyllopodiform genus Nehalia. 

 Hitherto two different genera of these animalcules have been 

 known, one of which was discovered by Grube f and intro- 

 duced into science under the name of Seison. Subsequently 

 Claus I recognized two distinct species {S. Oruhii and 8. an- 

 nulatus) in the animals described by the above-named natu- 

 ralist, and subjected these to a very thorough investigation. 

 The second genus which must be referred to the group of the 

 Seisonidaj was first described by P. J. Van Beneden § aud 

 C. E. Hesse under the name of Saccohdella. One of the 

 species discovered by these naturalists, Saccohdella nehalke^ 

 was erroneously placed by them with the Hirudinese, and 

 Claus first referred it to its proper place in the neighbourhood 

 of the genus Seison. As, however, the two representatives 

 of the latter differ considerably in the form of the body from 

 Saccohdella nebalioi^ their generic distinctness must be main- 

 tained, and it seems to me incorrect to cite the animal 

 described by the Belgian naturalists as a distinct species of 

 the genus Seison. How far the internal organization of 

 6'. nehalice agrees with that of the true Seisonidse cannot at 

 present be decided, as our knowledge of that Eotatorian is 

 still imperfect and in many points pressingly requires con- 

 firmation. The genus Seison also needs further investiga- 

 tion, because with regard to the sexual and excretory apparatus 

 many questions still wait for a definitive solution. This 

 circumstance induced me to devote a short sojourn at the 

 Zoological Station at Naples in the spring of 1886 to the 

 study of this interesting group of animals. 



* Translated from the ' Mittbeilimgen aus der zoologischeu Station zii 

 Neapel,' Bd. yii. pp. 234-2U3. 



t E. Grube, ' Eiu Ausfiug nacli Triest und dem Quarnero,' Berlin, 1861, 

 pp. 19 and 109-115, 



X C. Claus, " Ueber die Organisation und die systematische Stellung 

 der Gattung Seison, Gr.,'' in the Festschrift zur Feier des 2.5-jahrigi'n 

 Bestehen der k. k. zool.-bot. Ges. in Wien, 187G; and "Zur Kennlniss 

 der Organisation \o\-\ tSeisou," in ' Zool. Anzeiger,' 1880, no. 68. 



§ Van Beneden and Hetse, ' Recherches sur les Bdellodes ou I J irudinfes, 

 et les Trematodes niarius,' Brussels, 1803, pp. 48 d seqq. 



