TRACHYMEDUSAE. 



339 



Fig. 196. — Zygocannula diploconus 

 Medusen. 



after Haeckel, in Syst. der 



Zygocannula diploconus Haeckel. 



Zygocannula diploconus + Z. undulosa, Haeckel, 1879, 

 Syst. der Medusen, pp. 216, 217, taf. 15, fig. 6. 



Bell 60 to 100 mm. wide and higher 

 than a hemisphere. Numerous well- 

 developed radial ridges upon the exum- 

 brella. 50 to 70 long tentacles at the ends 

 of the branches of the radial-canals. 

 These tentacles are longer than the bell- 

 diameter. There are 200 to 300 small 

 lithocysts, each with a single concretion. 

 25 1035 radial-canals arise from the periph- 

 ery of the stomach and bifurcate, so that 

 50 to 70 canals reach the circular vessel. 

 The gonads are linear, folded, and devel- 

 oped upon the distal branches of the radial- 

 canals, leaving both ends of each branch 

 free. Medusa rose-red, gonads darker red. 

 Straits of Sunda, Indian Ocean, Haeckel. 

 Haeckel's description is derived from the 

 study of a preserved specimen. It may 

 be only an advanced stage of Zygocanna 

 pleuronota. 



Order TRACHYMEDUSAE Haeckel, 1866. 



Trachymedusa, Haeckel, 1S66, Generelle Morphol. der Organismen, Bd. 2, p. lix, Berlin. 



Trachomedusx, Haeckel, 1879, Svst. der Medusen, p. 234.— Maas, 1893, Ergeb. der Plankton Exped., Bd. 2, K.c, p. 6; 1897, 



Mem. Museum Comp. Zool. at Harvard College, vol. 23, p. 21 ; 1906, Fauna Arctica, Bd.4, Lfg. 3, p. 4S8, Jena. — Big- 



n iiw, 1909, Mem. Museum Comp. Zool. at Harvard College, vol. 37, p. 100. 



CHARACTERS OF THE ORDER. 



ree or inclosed lithocysts having concretions of entodermal origin. I 

 irgin, not cleft into lappets. The tentacles are usually solid, and 



Veiled medusae with free 

 With simple, entire bell-mar^ 



the gonads are commonly developed upon the radial-canals. There may be 4, 6, 01 8 radial 

 canals. The development is direct through a planula and an actinula stage, or by budding 

 from a stolon-like larva. 



The Trachymedusae, I believe, may be regarded as medusiform actinulae. In Aglaura, 

 for example, the tentacles of the actinula larva become those of the medusa, and the bell 

 grows out as an annulus from the sides of the actinula after some of the tentacles have become 

 fully developed. The lithocyst clubs of Trachymedusae contain entodermal concretions 

 which are evidently not comparable with the vesicular, ectodermal, velar concretions of the 

 Leptomedusae. It is probable, therefore, that theTrachymedusae and Narcomedusae are to be 

 regarded as actinulae which are not homologous with the Anthomedusae and Leptomedusae, 

 but have attained independently to a medusiform shape and appearance. 



In this connection it is interesting to recall the recent discovery of Woltereck, 1905, that 

 there is an apical sensory plate in the actinula larva of Sohnundella, and also in the actinulae 

 of Tubularia, and Dawydoff has found a Solmundella-like medusa with a complexly developed, 

 apical sense-organ above the stomach. In the Geryonidae, some or all of the larval tentacles 

 of the actinula degenerate before the medusa becomes mature, and other tentacles replace 

 them. In Craspedacusta the medusae are produced by budding from a stolon-like "hydroid." 



The Trachymedusae are distinguished from the Narcomedusae by their uncleft bell- 

 margin and simple annular velum. Frequently, but not invariably, the tentacles project from 

 the sides of the exumbrella and their entodermal cores penetrate the gelatinous substance to 

 the ring-canal. 



