ECOLOGY AND TAXONOMY OF Hdlimeda 111 



Halimedea opuntia Lamouroux (1812), p. 186; Halimeda opuntia Barton 



(1901), p. 18, Plate 2, Figs 19-27; Collins (1909-1918), p. 400, Plate 17, 



Fig. 156; Taylor (1928), p. 82; Taylor (1950), p. 80, Plate 39, Fig. 1; 



Egerod (1952), p. 397, Plate 37, Figs 19a, e, f; HUlis (1959), p. 359, 



Plates 2, 5-7, 10. 

 Halimeda multicaulis (Lamarck) Lamouroux (1816), p. 307. Flahellaria 



multicaulis Lamarck (1813), p. 302. 

 Halimeda opuntia f. typica Barton (1901), p. 20, Plate 2, Fig. 19; Taylor 



(1928), p. 83, Plate 10, Figs 5-7, Plate 11, Fig. 17. 

 Halimeda opuntia f. cor data (J. Agardh) Barton (1901), p. 20, Plate 2, 



Fig. 21. Halimeda cordata J. Agardh (1887), p. 83. 

 Halimeda opuntia f. triloba (Decaisne) Barton (1901), p. 20, Plate 2, Fig. 20; 



Taylor (1928), p. 83, Plate 10, Fig. 2; Taylor (1950), p. 81, Plate 40, 



Fig. 2. Halimeda triloba Decaisne (1842), p. 102. 



Plants compact or sprawling, often with both lateral and erect systems 

 of growth, holdfast region not restricted to the initial area but diffuse, with 

 patches of rhizoids occurring at intervals where the plant comes in contact 

 with the substratum, to 1 m or more in length; calcification moderate to 

 heavy; branches sometimes few but often numerous, arising in more than 

 one plane from successive segments; segments extremely variable, flat or 

 somewhat contorted, and frequently ribbed, cylindrical or oblong to 

 auriculate, the upper margin entire, undulate or lobed, to 7 mm long, 11 mm 

 broad, averaging 0-3-0-5 mm in thickness, with the occasional larger 

 segment. 



Cortex of up to five layers of utricles formed by dichotomies in the lateral 

 branches of the medullary filaments (that is, not utriculiform) ; outermost 

 utricles adhering slightly after decalcification or for as much as 6 [xm, 

 appearing somewhat rounded or hexagonal in surface view, 12-41 [xm in 

 surface diameter, 15-39(-50) [xm long in section ; secondary utricles 11-35 [jim 

 broad. 



Nodal medullary filaments uniting most commonly in pairs for a distance 

 of approximately 1-5 times the filament diameter, occasionally fusing in 

 threes but rarely in fours, seldom remaining separate; adjacent fused units 

 free or laterally attached for up to 25 [xm. 



Type locality. Jamaica. 



Habitat. This species sprawls over rock surfaces, fills crevices, 

 and produces ropes of thallus which grow at the bases of rocks or 

 sometimes traverse patches of sand, with attachment provided by a 

 multi-holdfast system. In water of about 0'3-0-5 m this species 

 sometimes provides about 90% cover of rock surfaces. 



In deeper water it may be associated with H. goreauii. It also 

 grows as clumps on Acropora. 



It is known from close to the surface to — 90 m. 



