ECOLOGY AND TAXONOMY OF Holimeda 149 



4, Section Micronesicae n. sect. 



Halimeda micronesica Yamada 

 Eigure 46. 



Halimeda micronesica Yamada (1941), p. 121, Eig. 15; Yamada (1944), 

 p. 29, Plate 5 ; Taylor (1950), p. 89, Plate 46, Fig. 2 ; Plate 47 ; HHlis (1959), 

 p. 364, Plates 3, 5, 6, 9. 



Halimeda orientalis Gilbert (1947), p. 126, Fig. 1. 



? Halimeda incrassata f. pusilla Barton (1901), p. 28, Plate 4, Pig. 44. 



Plants compact, spreading, to 10 cm tall excluding the rhizoidal region 

 which is often small but sometimes long and fibrous, the rhizoids not 

 noticeably interlaced with sand particles; calcification moderate; colour on 

 drying white or steel-grey, the surface usually dull ; branching, except for the 

 basal region, mainly trichotomous and complanate; basal segment larger 

 than the others and more or less reniform, its outer margin frequently 

 undulate, to 12 mm long, 18 mm broad, supporting numerous cylindrical to 

 subcuneate segments ; other segments occasionally slightly ribbed, sometimes 

 cylindrical but more commonly subcuneate to discoidal, the upper margin 

 entire to trilobed, to 7 mm long, 9 mm broad and averaging to 0-5 mm in 

 thickness. 



Cortex mainly of three or occasionally four layers of utricles produced by 

 successive dichotomies in the lateral branches of the medullary filaments; 

 outermost utricles usually separating on decalcification but in young 

 segments often slightly attached, usually appearing rounded in surface 

 view, 28-48(-55) [xm in surface diameter, 40-82(-94) (jim long in section, 

 borne two or four on each secondary utricle; secondary utricles generally 

 not constricted at their origin, 15-45 [xm broad. 



Nodal medullary filaments remairdng unfused although sometimes 

 adhering slightly with adjacent ones; filament walls in nodal region 

 thickened and usually somewhat pigmented. 



Type locality. Ants Atoll, near Ponape Island in the east 

 Caroline Islands. 



Habitat. Growing attached to rock in relatively exposed sites 

 such as inter-island channels of Enewetak Atoll. Rope-like non- 

 corticated extensions from segments provide additional attachment 

 and the resultant growth form is semi-prostrate. Known vertical 

 range for this species is — 1 m to — 37 m. 



Geographic distribution. Western and eastern Indian Ocean; 

 western Pacific, both north and south. 



This was the first species described in which the medullary filaments 

 continued unfused through the node. Barton (1901) mentioned such a 



