94 Papers from the Department of Marine Biology. 



Von Graff quotes, however, a passage from a letter written by von 

 Willemoes Suhm,* showing that myzostomids may correspond perfectly 

 with their host in colour pattern. The case mentioned is that of 

 Myzostoma horologium v. Graff on crinoids which were probably Coma- 

 tula rotalaria and Comatula Solaris. The passage runs as follows: 



"In der Arafura-See habe ich im vorigen Jahre einmal 80 Exemplare einer 

 grossen Comatula untersucht und fand circa auf jeder zehnten unsere 

 Schmarotzer. . . . Alle dieser Myzostomen waren, wie die Comatula, weiss und 

 schwarz gefleckt, und die ubrigen zahlreichen Schmarotzer des Thieres zeigten 

 dieselbe Farbung." 



The myzostomids found on the crinoids of Murray Island were very 

 numerous and belonged to several different species. Dr. C. L. Boulenger, 

 of Birmingham University, has been kind enough to undertake their 

 identification. They are in many cases very brightly coloured and 

 have pronounced colour patterns. Generally speaking, there are two 

 types of pattern. In the first concentric rings of bright and dark 

 pigment alternate. In the second the dorsal surface is ornamented 

 with radiating ridges, and these are usually free from pigment or very 

 light coloured. The ridges are thrown into relief by an edging of a 

 dark pigment (e. g., purple or black) ; the general ground colour between 

 the ridges as a rule approaches that of the crinoid on which the parasite 

 was found. One of these forms was very common on the dark green 

 or black varieties of Comanthus annulatum. The alternate black and 

 non-pigmented rings are in vivid contrast, but the myzostomid is thin 

 and the non-pigmented parts are so transparent as to be inconspicuous 

 against the dark ground of the host. This species seems to occur only 

 on the darker crinoids. In another species the same arrangement is 

 found, but much lighter hues prevail, green pigment alternating with 

 very light brown. The colours of the host were, unfortunately, not 

 noted. 



When the host is very light coloured the alternation of darker rings 

 does not occur. On a green variety of C. annulatum a specimen of 

 Myzostma was found which matched it perfectly. The greater part 

 of the body was bright green, but a few white spots represented a broken 

 ring of a lighter colour; the edge was relieved by dashes of black pig- 

 ment, while the cirri were brownish. A very magnificent example of 

 the second type of colouration was secured on October 24, 1913, on a 

 green form of C. annulatum. It resembled its host closely and was 

 comparatively inconspicuous. The general colour was a bright green ; 

 the ridges appeared greenish white, darker at the edges owing to the 

 addition of a granular pigment, and round each there was an intense 

 black line. An allied form was found on darker crinoids; there the 

 ridges were white or yellow surrounded by a darker line (in one case 



*von Willemoes Suhm, Zeits. f. wiss. Zool. Bd. xxvi, 1876. 



