MORPHOLOGY AND RELATIONS OF SIPHONOPHORA 17 



GARSTANG ON PHYLOGENY 

 Reduced to its elements Garstang's paper consists of some corrections of interpretation which permit 

 a more satisfactory alignment of the orders, and support the idea that the pelagic habit of the 

 Siphonophores results from a prolongation of a free-swimming larval phase, coupled with precocious 

 development and sundry adaptations of the ancestral characters, including budding. 



Garstang attractively rounded off his critical discussion of siphonophore phylogeny by suggesting 

 that a myriotheline relationship of Siphonanths is indicated by the resemblance of their lateral, 

 paddling (sic) bracts to the larval tentacles of the actinula of the hydroid Myriothela, which are aboral 

 in position, locomotive in function and precociously developed. But he thought that this relationship 

 of Siphonanths to Myriothela had to be reconciled with the corymorphine affinities of Disconanths 

 before the common origin which he suspected could be firmly assured. He suggested that Pelagohydra, 

 Siphonanths and Disconanths may in fact be independent pelagic offshoots from three different types 

 of gymnoblastic hydroid, the larvae of which failed to attach themselves but succeeded in keeping 

 afloat until their gonophores ripened. Pelagohydra absolutely, and Disconanths to some extent, may 

 be said to have survived, he continued, by adaptive aggrandizement of their oozooids at the expense of 

 their colonies, while Siphonanths, by precocious budding, elaborated the colony at the expense of the 

 oozooid. Rather surprisingly, Garstang did not mention another floating tubularid hydroid, Marge- 

 lopsis haeckeli; and had he been familiar with the little-known Siphonophore, Apolemia uvaria, I feel 

 sure that he would have commented on the fact that the unique feature it presents, namely the presence 

 of tufts of tentacles at various points on the nectosome, recalls the arrangement in Pelagohydra. 1 



RELATIONSHIPS BETWEEN SIPHONOPHORA AND HYDROIDA 

 Having noted Garstang's conclusions about the phylogeny of Siphonophora and their relationship 

 with corymorphine and myriotheline hydroids, let us now take a brief look at this group of hydroids 

 and the rest of the Hydroida (Anthomedusae) Capitata. Whenever these hydroids bud off medusae 

 they belong to the old Haeckelian family Codonidae, considered by medusologists to be a simple and 

 primitive group of Anthomedusae. The Capitata include hydroids which have two contrasting habits. 

 In one the oozooid secretes a permanent tube, simple or branched, attached to the substratum at its 

 basal end by a branching stolon. In the other we find either planktonic forms, or insecurely attached 

 solitary forms anchored by hydrocauline processes to the sand or mud. It is perhaps natural to ask 

 which of these two contrasting types appears to be primitive and which derivative. 



Kramp (1949) gave a most interesting review of the corymorphine hydroids, including several of the 

 less sedentary forms of which very little is known. He said that actinula larvae are unknown in this 

 family, but both Hartlaub (1907) and Rees (1937) have shown that actinuloid larvae or polyp buds 

 are indeed known. Kramp, who, in his important paper, nowhere mentioned either Garstang's (1946) 

 work nor that of Gronberg (1898) on the canals of Tubularia, presented an outline of the course which 

 he thinks has been taken in the phylogeny of a Tubularia line of hydroids and a Corymorpha line, 

 and he derived the solitary, anchored forms like Corymorpha from those with fixed stolons like the 

 Corynidae. From general considerations this seems to be most improbable, but I shall not attempt 

 myself to speculate on the detailed phylogenies of genera of hydroids within the Capitata. Garstang's 

 argument for the derivation of the sedentary forms like Tubularia and Pennaria with fixed stolons, 

 from the free forms like Corymorpha, was based on good evidence from comparative morphology. 



I have re-examined the type specimen of the latter and have made efforts to find detached medusae referable to it amongst 

 plankton hauls from the New Zealand region, but without success. I was interested to hear recently from Dr Elizabeth J. 

 Batham that Canterbury Museum, Christchurch, New Zealand possessed a second specimen of Pelagohydra. 



D XXVII , 



