REPORT ON THE SIPHONOPHORiE. 281 



Order IV. AURONECT^, Haeckel, 1888. 

 (Pis. I.-VII.) 



Auronectse, Hkl., System der Siphonophoren, p. 43. 

 Auroplwridee, Hkl., ibid., p. 6. 



Definition. — Sipkonophorse with a large pneumatophore, a corona of nectophores, a 

 peculiar aurophore, and a network of canals in the thickened trunk. Nectosome com- 

 posed of a horizontal corona of nectophores beyond the voluminous spheroidal pneumato- 

 phore, and a singular pneumadenia (the large subspherical aurophore), placed in the 

 dorsal median line of the corona. Siphosome spheroidal, ovate or turnip-shaped, with a 

 thick, bulbous, cartilaginous trunk, traversed by a dense network of anastomosing 

 gastro-canals ; its surface densely covered by numerous cormidia, each of which bears a 

 .single siphon with a tentacle, and one or more gonodendra. 



The order Auronectse is represented by a few Siphonophorse of the deep sea, which 

 were discovered by the Challenger, and which differ so widely in their entire organisation 

 from all other animals of their class, that it is impossible to place them in any of the 

 four other orders. The large apical pneumatophore, of an enormous size, is similar to 

 that of the Physalidse among the Cystonectse ; the corona of numerous nectophores 

 (wanting in these latter) resembles that of some Physonectse (Circalidse, Forskalidse) ; but 

 the remarkable organ of the nectosome which we call aurophore is found in no other 

 group of Siphonophorse, and is exclusively peculiar to the Auronectse. The same 

 holds good of the thickened bulbous trunk of the siphosome, which is traversed by a 

 network of anastomosing canals, similar to the fleshy or cartilaginous coenosome of the 

 Alcyonidse. 



The few species of Auronectse which I have examined were preserved in spirit in 

 rather good condition, and seem to represent two different families of this order, 

 Stephalidse and Rhodalidse. The smaller Stephalidse (with the genera Stephalia, 

 PI. VII., and Stephonalia, PI. VI.) seem to be allied to the Circalidse among the 

 Physonectse (Circalia, PL XXI. figs. 1-4). Their bulbous trunk exhibits an axial central 

 canal, with a mouth at the distal end (PL VII. figs. 40, 48). The tentacles are simple, 

 without tentilla. The second family contains the larger and more highly developed 

 Rhodalidse (Rhodalia and Auralia, Pis. I.-V). The axial central canal of the bulbous 

 trunk has here disappeared, or is replaced by a central cavity ; its distal mouth-opening is 

 lost (PL IV. fig. 15). The tentacles are compound, with a series of lateral branches 

 or tentilla, similar to those of the Forskalidse. The young larval forms of the Rhodalidse 

 seem to be little different from the adult Stephalidse. 



Nectosome and Siphosome. — The two main portions of the corm, swimming and 

 feeding body, are both distinguished in the Auronectse by a peculiar development. The 



(ZOOL. CHALL. EXP. — PART LXXVII. — 1888.) Hhhh 36 



