NARRATIVE OF THE CRUISE. 



315 



good for all the species of Myzostoma hitherto known, the differences between them 

 consisting mainly in the number and length of the cirri and in the relative thickness, 

 t ransparency, and mobdity of the body ; thus Myzostoma ylabrum, the first species ever 

 described, which was discovered in 1827 by F. S. Leuckart attached firmly by its hooks 

 to the disk of Antedon rosacea (Comatula mediterranea), is distinguished by possessing 

 ;i thick opaque disk and small wart-like cirri ; another species — Myzostoma cirriferum — 

 discovered in 1834 by J. V. Thompson, has a delicate transparent disk and long cirri ; it 

 is found upon the same species of Antedon, and moves about freely over the disk and 

 arms of its host. A third species, Myzostoma costatum, was found upon Comatula 

 multiradiata of the Red Sea by Leuckart in 1836. Finally, nine new species collected 

 by Professor Semper in the Philippines were described by Professor v. Graff in his Mono- 

 graph on the group published in 1877. 



Fig. 126. — A, Myzostoma Itih-ulor/ium from the dorsal surface ; B, the same, from the ventral surface ; both figures are magnified 

 6 diameters. C, Myzostoma quadrijilum, from the ventral surface ; magnified 12 diameters. D, Myzostoma folium , from 

 the ventral surface, with the pharynx far extended ; magnified 12 diameters. E, Slelechopus hyocrini, strongly com- 

 pressed; magnified 18 diameters. 



" The Report upon the Challenger collection 1 contains a description of 52 new species 

 in addition to the 15 already known, and also considerably increases our knowledge of 

 the anatomy and mode of life of the Myzostomida. The two most remarkable forms are 

 Stelechopus hyocrini (fig. 12Ge) already mentioned, and Myzostoma folium (fig. 126d) ; 

 both these species by their elongated form and the absence of suckers differ considerably 

 from the known species and appear to form a transition between the Myzostomida and 

 the Tardigrada ; the Myzostomida have been regarded by different authors as allied to 

 the Trematodes, Hirudinea, Chsetopoda, Crustacea, or Tardigrada ; Dr. v. Graff's obser- 



1 Zool. Chall. Exp., part xxvii., 1884. 



