410 MEDUSAE OF THE WORLD. 



Genus LIRIOPE Lesson, 1843. 



Liriope, Lesson, 1843, Hist. Zooph. Acalephes, p. 332. — Metschnikoff, 1881, Zeit. fur wissen. Zool., Bd. 36, p. 436 (develop- 

 ment); Arbeit. Zool. Inst. Wien., Bd. 6, p. 246. — Brooks, 1886, Mem. Boston Soc. Nat. Hist., vol. 3, p. 383.— Mm!, 1893, 

 Ergeb.der Plankton Exped., Bd. 2, K. c, p. 35; 1897, Mem. Museum Comp. Zool. at Harvard College, vol. 23, p. 24; 1904, 

 Result. Camp. Sci. Prince de Monaco, fasc. 28, p. 25. — Zoja, 1895, Archiv. fur Entwick. Mech., Bd. 1 und 2. — Van- 

 hoffen, 1902, Wissen. Ergeb. deutsch. Tiefsee Expedition, Valdivia, Bd. 3, Lfg. 1, p. 79. — Browne, 1904, Fauna and 

 Geog. Maldive and Laccadive Archipel., vol. 2, p. 738. — Bigelow, H. B., 1909, Mem. Museum Comp. Zool. at Harvard 

 College, vol. 37, p. 1 1 1 . 



Liriantha+ Liriope+ Glossoconus+ Glossocodon , Haeckei., 1879, Syst. der Medusen, pp. 286, 288, 292. 



The type species is Liriope exigua = Liriope cerasiformts Lesson, of the Mediterranean. 

 This form is probably identical with the following: 



L. appendiculata Forbes, 1848; L. exigua Haeckei, 1879; L. mucronata Gegenbaur, 

 1856; Hertwig, 1879; Haeckei, 1879; L. scutigera A. Agassiz, 1865; ( ?) L. cerasus Haeckei, 



While L. cerasiformts is Lesson's type, the oldest known species was described by Cham- 

 isso and Eysenhardt, 1821, from the Indian Ocean under the name Geryoma tetraphylla. 

 This is probably identical with S. rosacea and possibly also with L. exigua. 



GENERIC CHARACTERS. 



4-rayed Geryonidae with 4 radial-canals, 4 lips, 4 gonads, and one or more blind, centrip- 

 etal canals in each interradial quadrant. With 4 primary, solid, radial, 4 permanent, hollow, 

 radial, and 4 solid, interradial tentacles, all 12 of which may be found upon the medusa at one 

 and the same time. 8 inclosed lithocysts, 4 radial and 4 interradial. Development direct. 



Haeckei, 1879, divides the genus Liriope into four genera based on the presence or 

 (apparent) absence of blind centripetal vessels and of 4 or 8 tentacles. Metschnikoff, Maas, 

 and Vanhoffen have shown that centripetal canals are probably invariably present and range 

 from 1 to 7 in each interradial quadrant. The tentacles may range from 4 to 12, for the 4 

 primary tentacles are almost certain to be lost before the medusa becomes mature, and very 

 frequently the 4 solid, interradial tentacles are also lost, leaving only the 4 hollow, radial ten- 

 tacles. It is evident, therefore, that Haeckel's genera are separated upon fictitious distinctions 

 and should be abolished and classified under the old generic name Liriope. 



The development of Liriope has been studied by Metschnikoff and by Brooks. The 

 medusa develops directly from a free-floating, actinula-like larva (see L. mucronata and L. 

 scutigera). The 4 radial-canals are separated by 4 interradial adhesions of the entodermal 

 layers of the primitive stomach-cavity. The primitive, solid radial tentacles disappear and 

 the solid interradial and hollow radial tentacles develop. 



Zoja, 1895, carried out some interesting experiments upon Liriope. Normally the ento- 

 derm is formed by delamination from the inner ends of the cells of the blastula at the 16-cell 

 stage. If we mechanically divide the 2-cell stage into two separate cells, each component gives 

 rise to the entoderm when it has divided into 16 cells, and not at its 8-cell stage, as might possi- 

 bly have been expected. In other words, the isolated cells of the 2-cell stage behave as original 

 ova and recommence the process of forming the embryo. 



In common with other Trachymedusae the species of Liriope are very widely distributed, 

 being abundant in all warm seas although unknown from polar regions. The species are 

 exceedingly difficult to separate, for the shape of the gonads, length of peduncle, and number 

 of centripetal canals are apt to be variable, and also change greatly in appearance as growth 

 proceeds. Vanhoffen, 1902, concludes that the shape of the gonads affords the surest criterion 

 for the separation of species. He would group the species about the following type forms: 



(1) L. tetraphylla Chamisso and Eysenhardt, with long, oval, egg-shaped gonads. 



Indo-Pacific region. 



(2) L. eurybia Haeckei., with oval or leaf-shaped gonads. Atlantic and Mediterranean. 



(3) L. cerasifonnis Lesson, with heart-shaped gonads. 



(4) L. rosacea Eschscholtz, with gonads of the shape of an equilateral triangle. 



(5) L. lutkeni Haeckel, with 5-sided, maple-leaf-shaped gonads. 



