ECOLOGY AND TAXONOMY OF HaUmeda 115 



Cortex of up to four series of utricles with inner ones usually not 

 utriculiform ; outermost utricles generally adhering slightly after decalcifica- 

 tion, in surface view most commonly polygonal although occasionally 

 somewhat rounded with a covering lamella (Section I) sometimes evident, 

 diameter in surface view 14-30(-39) [xm, in section 14-32 \ivci long, more 

 than four supported by each secondary utricle; secondary utricles 

 10-18(-25) fxm broad. 



Medullary filaments numerous in mature segments, most commonly 

 united at the node in pairs or sometimes in threes for (52-)56-75(-87) [jtm, 

 occasionally completely separate ; nodal units sometimes adhering slightly. 



Type specimen. Marshall Islands, Bikini Atoll, Bikini Lagoon, 

 dredged at -55 m, W. R. Taylor 46-108, 29 March, 1946 (MICH; 

 isotypes in C, L, PC). 



Habitat. Known from — 1 m low tide to — 55 m. At the shallow- 

 est depths it grows erect on shallow ledges of coral rock, appearing 

 like a miniature bush. Sometimes growing in the vicinity are H. 

 distorta, H. gracilis and H. macrophysa. 



Geographic distribution. Northern Pacific Ocean. 



In a re-evaluation of some of the entities assigned to opuntia, this 

 and two other species were separated out by Colinvaux (1968a). A 

 discussion of characters is provided m that paper. 



Halimeda renschii Hauck 



Figure 31. 



Halimeda renschii Hauck (1886), p. 167; Hillis- Colinvaux (1975), p. 93. 



Halimeda batanensis W. R. Taylor (1973), p. 34. 



Halimeda opuntia f. renschii (Hauck) Barton (1901), p. 21, Plate 2. 



Plants compact, erect or somewhat repent, to 8 cm tall, from a non- 

 discrete base of matted filaments and sometimes loose particles of substrate 

 which may exceed 1 cm in largest dimension, but is not bulbous as in typical 

 Rhipsalian species; branching tending to produce a flat (plane) thallus; 

 lower segments of thallus may be obscured by the matted base, segments 

 commonly obtrianglar but sometimes transversely oval towards the apex 

 particularly in Pacific specimens, flat or faintly ribbed, to 4 mm long, 

 5 mm broad. 



Cortex of three or more series of utricles formed by dichotomies of the 

 lateral branches of the medullary filaments and hence not particularly 

 utriculiform; outermost utricles adhermg only slightly and sometimes 

 separating after decalcification, polygonal, but sometimes rounded with a 

 covering lamella sometimes present, (ll-)15-28(-38) [i,m in surface diameter, 

 20-33 [xm long in section; secondary utricles 14-8-22 [xm broad. 



