CHAPTER IV 



LARVAE OF BRITTLE STARS 



(MORPHOLOGY, PHYSIOLOGY, AND 



BEHAVIOR) 



EARLY DEVELOPMENT 



Information is available in the literature on the development of about 4% of 

 the known species of brittle stars. Of the approximately 2,000 species, 55 are 

 described as viviparous and nearly 30 as species with larval development; 48 

 species of larvae have been reported whose taxonomic position remains un- 

 clear. In brittle stars, three types of development are known: direct (viviparity 

 including brood care); development with planktotrophic larva; and develop- 

 ment with lecithotrophic larva. 



Egg 



According to Hendler (1975), there is no strict relationship between egg 

 size and type of development. Thus, in species with direct development the 

 egg diameter may range from 0.1 to 1.0 mm; a lecithotrophic larva develops 

 from an egg of 0.13-0.35 mm in diameter, and a planktotrophic larva from 

 an egg of 0.07-0.9 mm in diameter. There is, however, a relationship between 

 the disk diameter of brittle stars, type of development, and number of eggs 

 produced by a single family, species with planktotrophic larvae produce the 

 largest number of eggs. For example, Ophiocoma echinata, in which the disk 

 diameter is roughly 25 mm, spawn up to 1,000,000 eggs, while in Ophionotus 

 hexactis, with a large diameter of nearly 40 mm, only 100 eggs mature by 

 the spawning period. Ophiocoma echinata develops with planktotrophic lar- 

 vae while in Ophionotus hexactis development is direct (Hendler, 1975). The 

 eggs of brittle stars are often reddish, yellowish, or yellowish-brown (Mortensen, 

 1937; Olsen, 1942). 



