121 



Figure 82: Structure of the attachment disk of the brachiolaria of Coscinasterias calamaha 



(from Barker, 1978). 



ap — attachment papilla; c — coelom; ce — coelomic epithelium; ct — connective tissue; 



if — inner fibrils; is — intercellular space. Arrows indicate secretory granules. 



crown. The brachiolaria, so to speak, walks along the substrate, attaching and 

 detaching its brachiolar arms. Scouting may continue for a few seconds to one 

 hour. If the substrate is not suitable for settling, the larva straightens its arms 

 and swims away. If the substrate is satisfactory, the larva ceases "scouting", 

 alternately presses its brachiolar arms to the substrate, spreads them maxi- 

 mally apart, then lowers the attachment disk to the substrate. A firm contact 

 is ensured by the working of the attachment papillae situated on each side of 

 the disk. Cementation then commences, during which the secretion of the 

 cells of the attachment disk is discharged and binds the disk to the substrate. 

 This process takes one to several hours. Metamorphosis, which had already 

 begun in the pelagic period of larval life, terminates in the attached state. 

 After six to seven days the juvenile sea star is dislodged from the larval body 

 by means of the primary ambulacral podia and, thus freed, begins an inde- 

 pendent hfe (Barker, 1978; Strathmann, 1978). 



Lig|;it retards metamorphosis. Larvae of the family Asteriidae maintained 

 in a normal daily range of illumination completed metamorphosis within ten 

 hours at night, while larvae illuminated continuously for five days were not 

 able to metamorphose even though they had attached to the substrate (Dautov, 

 1979). 



Substrate selectivity is well developed in some species and lacking in 

 others. High selectivity is typical of lecithotrophic larvae (Strathmann, 1978). 

 The Brachiolariae of Acanthaster planci and Coscinasterias calamaria, plank- 

 ton feeders, settle on almost any substrate, provided it is covered with a 

 primary bacterial-algae film (Lucas, 1975, Barker, 1977). The microrelief of 

 the substrate is evidently not of special importance; however, the brachiolaria 

 in anchoring prefers, whenever possible, the lower surface of the substrate. 

 Yet some planktotrophic brachiolariae do exhibit high substrate specificity. 

 One such is the New Zealand sea star {Stichaster australis), which settles only 



