ECOLOGY AND TAXONOMY OF Holimeda 101 



at least — 58 m. At Enewetak Atoll it is sometimes associated with 

 stuposa, and of three Rhipsalian Halimedae present [incrassata, 

 stwposa and cylindracea), it was the commonest and grew in the 

 least exposed habitats. At Enewetak it was commoner in sandy 

 regions near coral patches than in open stretches of sand. This 

 distributional pattern may partly result from bioturbation. 



Geographic distribution. Western Indian Ocean, western Pacific, 

 both north and south. 



Holimeda stuposa Taylor 



Figure 25. 



Halimeda stuposa Taylor (1950), p. 90, Plate 43, Fig. 1; Plate 49; Plate 50, 

 Fig. 2; HHlis (1959), p. 374, Plates 3, 5-7, 11. 



Plants erect, rather small, thick-set, compact, to 10 cm tall excluding the 

 holdfast which is often massive, this generally extending to 5 cm in length 

 but on occasion to 13cm; calcification moderate; branching mainly ditri- 

 chotomous; basal segments subcuneate or compressed-cylindrical, often 

 forming a stipe or else consolidating laterally with adjacent segments to 

 form a short trunk-like structure; other segments plane or occasionally 

 ribbed ; subcylindrical or cylindrical, at times becoming subspherical towards 

 the apex, the upper margins entire to slightly lobed, to 7 mm long, 11 mm 

 broad and averaging 2 mm in thickness. 



Cortex of three to five layers of utricles; outermost utricles separating 

 slightly on decalcification or remaining attached for an average distance 

 of 4 [xm, their lateral and peripheral margins usually thickened, 

 21-48(-55) (xm in surface diameter, 50-80(-100) yun long in section, two or 

 more commonly four supported by each secondary utricle; secondary 

 utricles (17-)25-50 [xm broad, (23-)30-90(-125) [xm long; tertiary utricles 

 38-65 [xm broad. 



Nodal medullary filaments uniting as a single group for a distance of 

 approximately 30-50 [xm, the adjacent filaments communicating by pores; 

 walls in this region thickened and pigmented. 



Type specimen. Marshall Islands, Rongelap Atoll, Naen Island, 

 Taylor 46-591, 17 July, 1946 (MICH). 



Habitat. Grows in sand, mud or other unconsolidated substrate 

 from about low-tide line to at least —10 m, and sometimes develops 

 extensive stands. In places, it may be partially buried in shifting 

 sand, producing a very long holdfast which requires use of a trowel 

 or knife to extract it completely. Sometimes it is associated with 

 cylindracea. 



