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on coralline algae of the genus Mesophyllum. In the absence of a suitable 

 substrate, the sea star can delay completion of metamorphosis and continue 

 swimming; according to Barker (1977), its threshold of selectivity drops 

 gradually. If the larva is unable to find a suitable substrate, it dies. Larvae 

 of Acanthaster planci, Culcita novaeguineae, and Linckia laevigata, feeding 

 on corals, settle on the coral algae Porolithon (Yamaguchi, 1973, cited by 

 Chia et al, 1984); tubes of the polychaete Phyllochaetopterus prolifica attract 

 larvae of the sea star Mediaster aequalis, the young of which feed on these 

 polychaetes (Birkeland et al., 1971). 



Larvae of the families Luidiidae and Astropectinidae possess no special- 

 ized "larval" attachment organs. For scouting the substrate and temporary 

 attachment, the larva uses the already functional ambulacral podia of the 

 juvenile sea star (Strathmann, 1979). 



METAMORPHOSIS 



The metamorphosis of sea stars from planktotrophic larvae is catastrophic in 

 character. Intensive morphogenetic processes occur in which dedifferentiation 

 or resorption of many larval tissues takes place. The definitive sea star forms 

 on the left side of the larva. The oral-aboral axis of the sea star is at an angle 

 to the principal axis of the larval body. In most sea stars the principal and 

 concluding processess of metamorphosis are completed after the brachiolaria 

 has settled in the attached state. 



Digestive system : The ciliated band performs the function of a capturing 

 mechanism and organ of locomotion only in the larva and, in the course of 

 metamorphosis, is subjected, like the remaining areas of the larval epithelium, 

 to dedifferentiation and resorption. Cells of the preoral ciliated band are part 

 of the stalk whereby the developing sea star is bound to the attachment disk; 

 in some species the stalk is divested after metamorphosis, while in others it 

 is resorbed (Chia and Burke, 1978). The entire epithelium is not resorbed; the 

 definitive integument of the juvenile sea star is differentiated from its cells 

 (after the preceding dedifferentiation). The digestive system undergoes sig- 

 nificant changes. The larval tissues of the mouth, part of the gut, and the anal 

 region are resorbed. Cells of the larval esophagus constitute part of the outer 

 epidermis and wall of the stomach. A definitive esophagus is formed, the 

 larval stomach is reconstructed, and rudiments of the pyloric appendages 

 appear. According to Bury (1895), the larval esophagus is directly trans- 

 formed into a definitive organ. On the oral side of the juvenile sea star a 

 mouth opening appears and on the aboral side an anal opening. A definitive 

 gut with rectal glands forms from parts of the larval gut (Gemmill, 1914). 



