NO. II ECHINODERMS CLARK TT 



HELIASTER CUMINGII (Gray) 

 Plate 3, fig. 9 



Locality. — Galapagos Islands : Elizabeth Bay, Albemarle Island ; 

 south end of the black beach north of the mangroves north of the two 

 "red" islands. July 26, 1938. One specimen (U.S.N.M. no. E.5611). 



Notes. — In this specimen there are 21 arms; R = 30 mm., r = 16 

 mm. The spines on the abactinal surface are rather widely scattered 

 and are strongly capitate. They are single except in the midline of 

 the free portion of each ray where there are five groups, the inner- 

 most of 2 spines and the distal three of usually 3. sometimes 2, 

 rarely 4. 



The rays are of various lengths, showing that the animal is under- 

 going active ray reduplication. In addition to the perfectly formed 

 arms of various sizes, there are 4 arm buds all situated in interradial 

 openings having the appearance of rents in the aboral epidermal cov- 

 ering, the inner edge of which in all cases is 10 mm. from the center 

 of the disk, or 6 mm. within the bases of the free rays. 



These arm buds arise far below the aboral epidermal covering, 

 apparently between the upper portions of the proximal marginal 

 plates of 2 adjacent rays, and grow upward. The tip is provided with 

 a terminal row of 4 and a subterminal row of 5 short stout spines 

 armed with stout low conical spinelets. The furrow spines are well 

 developed. When the growing arm bud reaches the epidermal cov- 

 ering the latter is ruptured, and the edge of the rent draws away from 

 the arm bud leaving a conspicuous opening. 



The arm bud now grows outward and slightly downward, parallel 

 with the aboral surfaces of the adjacent rays, the tip, however, remain- 

 ing turned up at right angles to the rapidly extending newer growth 

 which, becoming deeper and developing a dark epidermal covering 

 with the usual capitate spines, rapidly repairs the inner portion of the 

 rent, at the same time extending it toward the interbrachial border ; 

 on reaching the interbrachial border the arm bud grows outward into 

 an arm of the typical form. 



The tube feet in the arm buds, as in the fully developed arms, are 

 in 2 rows which are slightly zigzag, alternate tube feet being nearer 

 and farther from the midline of the groove. 



The largest of the arm buds, which reaches to within 4 mm. of the 

 interbrachial angle, beyond the end of which the rent extends entirely 

 through the animal from the aboral to the oral side, is visible on the 

 oral surface, were it separates 2 of the arms for about half the dis- 

 tance from their bases to the interbrachial angle. It appears as a small 



