126 



Figure 85: Brachiolaria of Echinaster echinophorus (from Atwood, 1973). 

 ad — attachment disk; br — brachiole; hp — hydropore. 



sanguinolenta (Masterman, 1902), Leptasterias hexactis (Chia, 1966) Patiriella 

 exigua (Lawson-Kerr and Anderson, 1978), and Asterina minor (Komatsu et 

 al., 1979). Brachiolar arms are absent in some species — Asterina gibbosa 

 (McBride, 1896); in other species, they are developed but the attachment 

 stage is absent — Echinaster sepositus (Nachtsheim, 1914) and Asterina 

 batheria (Kano and Komatsu, 1978). The lecithotrophic larva of Astropecten 

 latespinosus possesses neither brachiolar arms nor attachment disk (Komatsu, 

 1975), which is not at all strange since the brachiolaria stage is absent in 

 astropectinids with planktotrophic larvae. Due to lecithotrophy, the number 

 and degree of development of larval structures are minimal and the definitive 

 organogenesis of such larvae proceeds in a more direct manner. 



On the whole, it may be said that the secondarily acquired direct devel- 

 opment or development lecithotrophic larva is often observed in evolutionally 

 primitive groups of sea stars. (A similar picture is observed in many taxa of 

 invertebrates, for example in bivalves.) In the primitive order of sea stars 

 Paxillosida, direct development with brooding of offspring in the cavities 

 between paxilli occurs in the genera Ctenodiscus and Trophodiscus. In T. 

 almus the largest embryos are located along the margin of rays and in the 

 interradii of the female. Embryos emerge through movement of the paxilli. 

 Similar brooding is observed in T. uber (D'yakonov, 1950). Development 

 without free-swimming larvae is also typical of Solaster endeca, Crossaster 

 papposus, Asterina gibbosa, and other species of the latter genus. In Pteraster 

 obscunis and P. militarise fertilization and brooding of embryos occurs on the 

 dorsal side within a special cover (Kaufman, 1977). In species of the genus 

 Henricia, embryos are borne in clutches near the mouth or in the mouth of 

 the mother. Development without planktotrophic larva occurs in the order 



