ECOLOGY AND TAXONOMY OF Holimeda 25 



Zanardini (1851, 1858), Kiitzing (1857-1858), Piccone (1879), Hauck 

 (1886), Agardh (1887) and Askenasy (1888), changing the species 

 total from 5 to 27 in about 50 years. Not all of these species proved 

 satisfactory, however. Until 1888, the taxonomy was based almost 

 entirely on external characteristics, with emphasis on what is now 

 recognized as an exceedingly variable character, "segment shape". 

 The microscope was not used critically for identification and Kiitzing 's 

 statement (1857), that internal organization was uniform among the 

 species of Halimeda, provides some insight into the "state of the 

 science" at that time. With such heavy reliance on segment shape, it is 

 not surprising that certain taxa such as opuntia, and to a lesser extent 

 incrassata, both of which commonly show a large variety of segment 

 types, were at one time each described as more than one species. 

 Segment shape, along with habit, also formed the basis of Agardh's 

 (1887) sections within the genus which subsequently have been ignored 

 (Hillis, 1959), at least partly because of their unsatisfactory definition. 



The cornerstone of critical modern taxonomy and microscopy for 

 the genus was laid by Askenasy (1888) who used microscopic characters 

 to distinguish the few Halimeda species collected during an expedition 

 of the S.M.S. Gazelle, as well as to delimit the new species macrophysa. 

 Of special significance was the fusion he described of medullary filaments 

 at the node in the species incrassata (Table III, Type 1). A brief 

 reference to altered medullary filaments at the node, made by Agardh 

 (1887) and by Ellis as early as 1755, provided some microscopic 

 observations, but Askenasy's work represents the first detailed account 

 of a major microscopic characteristic. 



Askenasy not only emphasized nodal patterns of medullary filaments 

 but also discovered that the sizes and shapes of peripheral utricles 

 ("Rindenschlauche") differed significantly among taxa. He also pro- 

 vided a very clear description of the calcium carbonate deposits 

 within Halimeda, pointing out that the crystals develop in the spaces 

 outside the filaments, but within the confines of the segment, that is, 

 that calcification is not external to the segment. The perceptive 

 account shows his skills as an able contemporary microscopist and 

 investigator. Little was added to this description until the 1960s 

 (Lewin, 1962), when the tools of electron microscopy and radioisotopes 

 became available. 



C. The discovery at Funafuti: the reef-building capabilities 

 of Halimeda 



At the close of the nineteenth century the Royal Society and the 

 Government of New South Wales sponsored an expedition to Funafuti 



