350 THE LIVING ANIMALS OF THE WORLD 



!, F.Z.S.] 



THICK-SPINED SEA-URCHIN 



In large ifecimeni tkt if inn are ai thick at a tlaie-ftnci/, and may be uud 

 for tke tame purpeu 



of the class. Thus, in the COMMON 

 Si \k-KI si I, there arc five so-called arms, 

 five eye-spots, one at the tip of each 

 arm, and nve equivalent elemental 

 components of all the more impor- 

 t nit viscera. In the SEA-CWl MM RS, 

 which have elongate worm-like bodies, 

 there is a similar apportionment of 

 the nerves and muscles of the body 

 generally into fives, and also of the 

 branching tentacles which surround 

 the mouth. Tubular locomotive organ*, 

 the so-called " tube-feet," are common 

 to all the three types enumerated. 

 The calcareous plates and spin 

 while attaining to a maximum develop- 

 ment in the urchins, are also abundantly 

 represented in the other groups. In 

 the common star-fish these calcareous 

 elements form within the skin an 

 openly reticulated trellis-like frame- 

 work, while in the ordinary sea- 

 cucumbers they more usually take the form of innumerable microscopically minute spiculcs. 

 The two less familiarly known groups of the FEATHER-STARS and BRITTLE-STARS fully agree 

 with the previously enumerated types in their five-fold structural composition. The brittle- 

 stars have almost invariably five arms only, but they are independent outgrowths from the 

 body proper, instead of being prolongations of it, as in the common star-fish. 



The FEATHER-STARS, which include some of the rarest anil most beautiful representatives 

 of the group, are mostly inhabitants of deep water, and remarkable for the circumstance that 

 either throughout life or in their early phases they are affixed to submarine objects by slender 

 stalks. This peculiarity imparts to the animals such a flower-like aspect that, in conjunction 

 with the indurated calcareous nature of their skeletons, they have received the title of 

 " Stone-lilies." This appellation, however, was originally more particularly applied to their 

 fossilised remains, which occur in remarkable abundance in the older geological strata. 



The most familiar representative of the group is the ROSY FEATHER-STAK. occasionally 

 obtained among seaweed in rock-pools on the southern coast, but more often brought up with 

 the dredge from deeper water. In this form the elongate feather-like amis radiate from the 

 central, relatively small, five-rayed body. There is no supporting foot-stalk in this adult st. 

 the animal being freely movable, and clinging to seaweeds and other objects by* means of a 

 cluster of claw-like filaments developed upon its under-surface. Releasing its IK .Id upon 

 its temporarily selected position, it can crawl about with the aid of the hooked extremities of 

 its arms and their radiating joints. It can also propel itself through the water in a somewhat 

 clumsy fashion by the consecutive flexion and extension of these appendages. This freedom 

 of locomotion was not, however, always possessed by the feather-star. In its early day-, and 

 when of very small size, it was affixed to a slender foot-stalk, and dependent for its food on 

 the animalcules and other minute organisms which drifted or swam within reach of its extended 

 arms. The rosy feather-star takes its name from the bright rose-red tints by which it is 

 usually characterised. Individuals of the species are, however, subject to considerable colour- 

 variation. On the Australian coast, where many forms are abundantly represented, examples 

 tinted deep crimson, black, bright golden yellow, or sundry admixtures of these several hues 

 are not uncommonly found associated among a dredge-haul of these elegant sea-stars. 



The I'l-KMAM \TI.Y STALKED SlM-l II.II> are at the present day of ''are occurrence. I'p 



