SHALLOW- WATER STARFISHES 7 



sandy bays and harbors. Some of the species have more than six 

 rays. In all cases the rays are long, flattened, and very flexible. 

 Ordinarily when at rest they lie just beneath the surface of the sand, 

 which soon forms into star-like impressions, agreeing with the star- 

 fish in size and form. This is due to the minute currents of water 

 produced by the ciliary motions connected with the respiration of 

 the starfish by means of the dorsal papulae. 



When disturbed, the starfish glides away quickly, just under the 

 loose superficial sand, using its " sucker-feet " or " ambulacral feet " 

 as paddles for swimming or gliding. These ambulacral feet are 

 much larger and longer than usual and are much flattened trans- 

 versely, and have no terminal sucker, but end in a point. They are 

 very muscular and can be waved back and forth, like paddles, in 

 unison, so that the motion is more like rowing or swimming than 

 running or creeping. While under the sand, no doubt the pressure 

 against the sand causes them to act something like legs or feet ; but 

 when placed in an aquarium without sand, they can swim or glide 

 along the bottom and up the perpendicular sides with surprising 

 rapidity. 



My own observations on this genus were made in 1901, at Ber- 

 muda * on Luidia clathrata Say, a five-rayed species. 



Similar observations have since then been made by others on 

 different species of Luidia, so that this mode of locomotion is prob- 

 ably common to all the species of the genus. 



LARVAL STAGES; PROTECTION OF EGGS AND YOUNG; 



INCUBATION. 



The wide and rapid distribution of many, if not most, starfishes of 

 shallow seas is, however, due to the fact that nearly all produce vast 

 numbers of minute eggs, which develop into small, singular, bilateral, 

 free-swimming larval forms (bipinnaria, brachiolaria) that require 

 many days or weeks to go through their metamorphoses before set- 

 tling down to the bottom in the starfish form. While in these larval 

 stages, they may be drifted long distances by waves and currents and 

 finally settle down in places far from their place of origin. Of course, 

 in most cases they become widely dispersed and vast numbers perish, 

 but sometimes, on the other hand, myriads of young may happen to 

 drift along in company, by the action of a current, and so finally 

 locate as a vast colony in a new home. 



1 A. E. Verrill, 1901, p. 36, and Zoology of Bermuda, Article 10, p. 36, 1903. 

 (See Bibliography.) 



