MJ MEDUSAE OF THE WORLD. 



Genus MARGELOPSIS Hartlaub. 



Nemopsis (hydroid only), MCCRADY, 1857, Gymn. Charleston Harbor, Proc. Elliott Society of Charleston, vol. I, p. 163, plate 



10, figs. 4-7. 

 Marsehftshi HARTLATB, 1897, Hydromedusen Helgolands, Wissen. Meeresuntersuch., Biolog. Anstalt auf Helgoland, Neue 



Folge, Bd. 2, p. 48z; Ibid., 1904, Bd. 5, p. 99; 1899, Nachrich. k. Gesell. der Wissenschaften Gottingen, math.-phys. 



Klasse, p. 219; Zool. Centralbl., Bd. IO, p. 28; 1907, Nordisches Plankton, Nr. 12, p. 88. BROWNE, 1903, Bergens 



Museums Aarbog, No. 4, p. 10. MULLER, 1908, Zeit. fur wissen. Zool., Bd. 89, pp. 43, 73. 



GENERIC CHARACTERS. 



Anthomedusae with simple, round mouth-opening without oral tentacles, or cruciform 

 lips. With 4 radially placed clusters of marginal tentacles and 4 radial-canals. The ring- 

 like gonad encircles the stomach. The hydroid is the pelagic Margelopsis. 



The tentacles of the hydroid are confined to definite whorls. In 1857, McCrady described 

 a free-floating hydroid from Charleston Harbor which has two whorls of tentacles, and between 

 them a number of medusa-buds arise from the sides of the hydranth. When set free the 

 medusas bore some resemblance to Nemopsis, and McCrady believed them to be the young 

 of Nemopsis gibbesn = Nemopsis bachei L. Agassiz. We now know this to have been a 

 mistake, for Hartlaub, 1899, discovered that actinula larvae develop upon the sides of the 

 manubrium in Margelopsis haeckehi. Then these actmulae are set free with two whorls of 

 tentacles, and medusa-buds develop from the sides of the hydranth between the whorls, and 

 are set free, as in McCrady's hydroid, which is, indeed, a species of Margelopsis. 



In 1904 Hartlaub found another free-floating hydranth (Margelopsis stylostoma) which 

 is apparently detached from Tiarella singularis F. E. Schulze. It is apparent that the Siphon- 

 ophoras may have been derived from hydroid forms having a similar life-history. 



The medusas of this most interesting genus appear to form a connecting link between 

 the Codonidae and Margelidae of Haeckel. They resemble the Codonidae in their simple 

 mouth-opening without oral tentacles or prominent lips, and in the single ring-like gonad 

 surrounding the manubrium. On the other hand, they resemble the Margelidae in having 

 the marginal tentacles grouped into 4 radially situated clusters. There are, however, no 

 tentacular ocelli such as are seen in the Margelidas. 



The Atlantic species are all very closely related and may prove to be but one. The 

 chief distinctions are the number of tentacles upon each tentacle-bulb. For example: M. hart- 

 lanlm Browne has 2; M. haeckeln Hartlaub has 3 to 4; M. gibbesi Hartlaub has 510 6. 



The medusa of M. stylostoma, and the hydroid of M. hartlaubii are unknown, and it is 

 possible that these two may be phases in the life-history of one and the same animal. 



The so-called "Perigonimus sulphureus" Chun, 1889 (Sitzungsber. Akad. Wissen. Berlin, 

 Jahrg. 1889, p. 524), and Steche, 1906 (Zool. Anzeiger, Bd. 31, p. 30, 2 figs.), is probably 

 not a Perigonimus, but may give off pelagic hydranths. Chun found this hydroid grow- 

 ing upon a living shell of ffyaliea in the Canary Islands. One portion of the net-like 

 hydrorhiza gives rise to isolated polypites, and another portion to the medusa-buds. The 

 hydranths arise directly from the hydrorhiza and are unbranched. They are barrel-shaped, 

 large, and with an oral circlet of 6 to 9 short, blunt tentacles. One of the hydranths was sharply 

 constricted by a ring-furrow in the middle of its length as if the oral end were about to be set 

 free and to become pelagic (Steche). The medusa-buds also arise singly from the hydrorhiza, 

 each of the medusa-buds being placed upon a short, unbranched peduncle. When set free 

 the medusas have 4 short tentacles with swollen basal bulbs, and the manubrium does not 

 project beyond the velar opening. The entoderm of the hydroid and medusa is sulphur- 

 yellow. The periderm of the hydroid is smooth and has none of the foreign bodies attached 

 to it such as are seen in Perigonimus. According to Steche the colony feeds upon the eggs 

 which are set free by the Hyaliea on which it grows. 



Margelopsis haeckelii Hartlaub. 



Margelopsis hxckelii, HARTLAUB, 1897, Wissen. Meeresuntersuch. Kommis., Meere Kiel, Helgoland, Neue Folge, Bd. 2, p. 482, 

 taf. :6t, fign. 12-18; 1899, Nachricht. kg!. Gesell. Wissen. math.-phys. Klasse, Gottingen, Jahre 1899, p. 219, 3 fign.; 



1907, Nordisches Plankton, Nr. 12, pp. 89, 91, fign. 84-86 (best published description of hydroid and medusa). MULLER, 



1908, Zeit. fur wissen. Zool., Bd. 89, pp. 43, 73, taf. 5, fign. 18, 19. 



