213 



Figure 166: Amphioplus abditus (Hendler, 1977). 



Three stages of development of brittle stars within the envelope. 



A — prism stage; B — first separation of the rudiments of the juvenile; C — formation of 



rudiments of the ambulacral podia and mouth. 



In the case of a larva of the doliolaria type development up to the gastrula 

 does not differ from development of a planktotrophic larva. The blastopore 

 closes early in the gastrula. The preoral lobe develops at the anterior end and 

 the oral opening itself is shifted to the posterior end. 



Separation of the left hydrocoel, forming five rudiments of the various 

 canals of the ambulacral system (Figure 1 68), begins before the formation of 

 ciliated bands. Then, in the place of a uniform ciliary cover, four transverse 

 ciliated bands are formed, as in doliolariae of sea cucumbers. One of the bands 

 passes at the level of the oral opening, near which it becomes discontinuous 

 (Figure 169). At this stage, in some brittle stars, rudiments of the larval skeleton 

 become visible (in Ophiolepis cincta — Mortensen, 1938). Then the posterior 

 part of the larva gradually acquires a pentagonal shape and the larva descends 

 to the bottom where metamorphosis is completed (Figure 170). 



With reference to the settling of doliolaria-type larvae, Stancyk (1973) 



