ASTEROIDEA 41 



It is only rarely infested with Myzostoma {M. Carpenteri 

 Graff). A small Isopod, Miinna Boecki Kroyer, is not infrequently 

 found on its arms, crawling about among its pinnules and gnawing 

 off its tube-feet — which does not appear to irritate the sea-lily. 

 On account of its grey colour the Isopod is very difficult to observe 

 on the sea-lily. 



Known in British seas from S.W. of Ireland to the Shetlands, 

 from depths of ca. 300-500 ms. (The Antedon tenella recorded 

 from Lousy Bank is probably this species.) Elsewhere widely 

 distributed in the North Atlantic (Faroes, Iceland, S.W. Green- 

 land) and along the Norwegian coast to Finmark. Also off 

 the American coasts it is found in deep water southward to 

 Massachusetts and New York. Known bathymetrical distribu- 

 tion, 28-1783 metres. 



A very closely related form, Hathrometra tenella (Retzius), 

 occurs at the east coast of N. America. It is distinguished 

 through the somev/hat larger number of cirrus-segments (mostly 

 27-30), and is, upon the whole, somewhat larger (arms usually 

 85-100 mm. long, in H. Sarsii rarel}^ more than 85 mm. long). It 

 seems, however, doubtful whether the two forms can be main- 

 tained as separate species ; they are probably only varieties of one 

 and the same species. If the latter view is correct, the European 

 form should be named Hathrometra tenella, var. Sarsii (Diiben 

 and Koren). 



II. Class. SEA-STARS i or ASTEROIDS 

 (Asteroidea) 



Free-living echinoderms, with a flat, star-shaped, or penta- 

 gonal body. Tube -feet in an open furrow along the underside 

 of the arms, which are, as a rule, not sharply marked off from the 

 disk. The arms contain the genital organs and the " j^yloric 

 caeca " (liver). Stomach large, sac-shaped ; intestine rudimen- 

 tary; anal opening small or wanting. Mouth turning downwards. 



The body of the sea-stars is of very different size, in accordance 

 with the development of the arms. The arms or rays may be very 

 short and broad — in this case the body or the disk is large, the 



^ It has been thought desirable to use the designation " sea-stars " for 

 this class of animals instead of the more popular but misleading " star- 

 fishes" ; " sea-star" also is preferable as corresponding to the designation 

 used in most other civilised languages — ■" Seestern ", " fitoile de mer ", 

 " S0stjerne ", etc. 



