215 



Figure 170: Ophiolepis cincta (Mortensen, 1938). 



Arrangement of primary plates of the definitive skeleton. 



A — oral side of the juvenile; B — aboral side of the juvenile. 



Ophiuroidea is the only class of echinoderms in which dwarf males are 

 found. It is not clear if all brittle stars with dwarf males (four species are 

 known to date) have brood care as in bivalves (see Chapter 1); however, in 

 Astrochlamys bruneus, in which dwarf males perch on the aboral surface of 

 the females, viviparity has been observed. 



In viviparous brittle stars the development of the young occurs in the 

 female bursae. The number of embryos is small, usually one or two. How- 

 ever, the number of developing embryos is sometimes fairly large. Murakami 

 (1941) — cited after Hendler, 1975 — found up to 70 individuals in 

 Stegophiura sculpta and Mortensen (1936) up to 200 individuals in 

 Astrochlamys bruneus in each bursa. 



Does viviparity actually occur in brittle stars? Or do we observe only 

 brood care in brood chambers, as in sea urchins and sea cucumbers? For many 

 species, this problem has yet to be solved. Only one comprehensive work is 

 available on the development of Amphipholis squamata (Fell, 1946), in which 

 viviparity has been confirmed. Fell demonstrated that the developing embryos 

 were attached to the horn of the bursa and not to the ovary. After differen- 

 tiation of layers in the embryo, the latter was surrounded by the wall of the 

 horn. At the site of attachment of the embryo to the horn of the bursa, the 

 parental and embryonal tissues fused. Later, the stalk on which the develop- 

 ing embryos are suspended in the bursal cavity appeared at this site. In his 

 earlier works. Fell proposed that feeding of the embryos is accomplished 

 through this stalk. In a later work, (Fell, 1946), he suggested that this stalk 

 is used only for attachment. 



