570 MEDUSA OF THE WORLD. 



The medusae of this family are readily distinguished from the Coronatae by the absence 

 of a coronal furrow and by the remarkable development of the 4 perradial corners of the 

 mouth, which extend outward as 4 long palps or mouth-arms, carrying the free edge of the 

 lips along with them in double cunain-iike fringes. Also the exumbrella of the Pelagidae is 

 smooth and displays none of the complex sculpturing seen among the Coronatae; finally, the 

 gastrovascuiar system of the medusae of the Pelagidae is simpler than in the Coronatae, for 

 the central stomach is without interradial fusions of its upper and lower walls, and it con- 

 sists merely in a wide, lenticular, central space which gives off completely separated, radiating 

 pouches in the radii of the tentacles and sense-organs. 



The Pelagidae are also closely related to the Cyaneidae. In the C)'aneidae, however, the 

 tentacles arise from the floor of the subumbrella at some distance in from the bell-margin, 

 whereas in the Pelagidae they arise from notches between the marginal lappets. Also the 

 tentacles ot the Cyaneidae are usually grouped in clusters, while in the Pelagidae they arise 

 singly. A still further distinction lies in the fact that the radiating pouches of the stomach 

 are simple in the Pelagidas, while in the Cyaneidae they give forth numerous blindly ending, 

 non-anastomosing canals, which enter the marginal lappets. 



Medusae of the genus Pelagui develop directly from the planula without going through a 

 sessile scyphostoma stage. The planulae of Chysaora and Dactylonirtra, however, attach 

 themselves and develop into Scyphostomae, which in the case of Chysaora is known to strobi- 

 late and produce a number of ephyrae. 



The Pelagidae are of world-wide distribution, but are most abundant in the tropical 

 regions. Man)- of them congregate in great swarms in bays and estuaries, and none are known 

 to live permanentl)- at great depths. 



The development of Pelagia has been studied by L. Agassiz (Cont. Nat. Hist. U. S.) and 

 by A. O. Kowalevsky, 1874 ("Memoirs of the Imperial Society of the Friends of Natural 

 History, Anthropology and Ethnography of Moscow, vol. 10, p. 7, plate 3 [Russian text]). 

 A synopsis of the genera of the Pelagidae follows : 



Pelagia PiRON and Lesueur, 1809. With 8 marginal sense-organs. 8 tentacles alternating with 8 marginal sense- 

 organs, 16 marginal lappets. 



Chrysaora PtRON and Leslei'r, 1809. With 8 marginal sense-organs. (3 X 8) 24 tentacles, 3 between each successive 

 pair of marginal sense-organs. 32 marginal lappets. 



Dactyhmelra L. Agassiz, 1S62. With 8 marginal sense-organs. (5X8) 40 tentacles, 5 between each successive pair 

 of sense-organs. 48 marginal lappets. 



Kuragea Kishinouve, 1902. (7 X8) 56 tentacles, (8 X8) 64 lappets. 



Sanderia Goette, 1886. 16 marginal sense-organs, 16 tentacles, 32 cleft lappets. 



Genus PELAGIA P^ron and Lesueur, 1809. 



Pelagia, PiRON et Lesueur, 1809, Ann. Mus. Hist. Nat. Paris, tome 14, p. 349.— Eschscholtz, 1829, Syst. der Acalephen, 

 p. 72.— .^<;AsslZ, L., 1862, Cont. Nat. Hist. U. S., vol. 4, p. 163.— Haeckel, 1880, Syst. der Medusen, p. 504.— Van- 

 HOFFEN, l888,Bibliotheca Zoologica,Bd. I.Heft. 3, pp.6, 21; 1902, Wissen. Ergeb. deutsch. Tiefscc Expedition, I'aldivia, 

 Bd. 3, Lfg. I, p. 34; 1906, Nordisches Plankton, Nr. 11, 14, 5.~Maas, 1904, Result. Camp. Sci. Prince de Monaco, 

 fasc. 28, p. 56; 1906, Revue Suisse de Zool., tome 14, p. 100: 1903, Scyphomedusen der Siboga Expcd., Monog. 1 1, p. 29. 



GENERIC CHARACTERS. 



Pelagidae with 8 adradial tentacles, alternating with 8 rhopalia. With i6 marginal 

 lappets. i6 radiating stomach-pouches in the rhopalar and tentacular radii, each of which 

 ends in 2 side branches in the marginal lappets. No ring-canal. 



The type species is Pelagia noctiluca of the Mediterranean, first described by ForskSl, 

 1775, as Medusa noctiluca. At least 14 so-called "species" of Pelagia are known, I from the 

 Mediterranean, i from the Mediterranean and Atlantic, 6 from the Atlantic, 5 from the 

 Pacific, and I from the Indian Ocean. They are more abundant in warm or torrid regions, 

 but one species is found in IJehring Sea and another near the Cape of Good Hope. All of 

 the Atlantic species arc closely related one to another, and future researches may demonstrate 

 that they are only geographical races. In fact the distinctions between "species" have been 

 largely determined upon preserved material, and some of them may he separated upon un- 

 natural conditions of contraction due to the effects of preservation; thus Vanhoff"en, 1888, 

 distinguishes a number of "species" upon the folding and wrinkling observed in the exum- 

 brella wans of preserved medusae. .At present the "species" are in almost hopeless confusion, 

 as will appear from the following table based largely upon Vanhoffen's work. Indeed it 



