212 



Figure 165: Ophiothrix fragilis (McBride, 1907). 



Transverse section. Appearance of primary gonads. 



axel — left axocoel; mp — madreporic pore; pg — primary gonads; phc — perihemal canal; 



stc — stone canal. 



young brittle stars are capable not only of creeping on the substrate, but also 

 swimming over the bottom as well, for which they use the remains of the 

 ciliated band. 



LECITHOTROPHIC LARVAE 



Some brittle star species have lecithotrophic larvae, which are similar to 

 planktotrophic larvae; these are, for example, Amphiura filiformis ( Mortensen, 

 1931), Amphiura chiajei (Fenaux, 1963), and Ophiothrix oerstedi (Mladenov, 

 1 979). Other species have larvae of the doliolaria type; these are Ophioderma 

 brevispine (Grave, 1916), Ophiolepis cincta (Mortensen, 1938), Ophioderma 

 longicauda (Fenaux, 1969), and Ophiolepis elegans (Stancyk, 1973). Devel- 

 opment of the third group of species is close to direct; these include 

 Gorgonocephalus caryi (Patent, 1970a) and Amphioplus abditus (Hendler, 

 1977). The development of the latter group of species is interesting in that 

 the egg membrane persists until the young brittle star hatches, although until 

 the prism stage it does not differ in development from planktotrophic larvae, 

 and rudiments of the larval skeleton remain up to much later stages (Figure 

 166). Thus, this type of development resembles the development of gastro- 

 pods in clutches or capsules. 



Generally, in any type of development with a lecithotrophic larva, cleav- 

 age and formation of the blastula proceed in the same maimer as in the case 

 of a planktotrophic larva. If in the process of development the larval skeleton 

 is formed, then it, too, develops as in a planktotrophic larva (Figure 167). 

 Amphiura chiajei (Fenaux, 1963) and Ophiothrix oerstedi (Mladenov, 1979) 

 develop only the posterolateral arms. 



