156 ARCHTCCELOMATA. 



CHAPTER XV. 



ARCHICCELOMATA. 



ASTERIAS. BALANOGLOSSUS. LOPHOPUS. SAGITTA. WALDHEIMTA. 



I.— ASTERIAS. 



Phylum . . . . Archiccelomata. 

 Sub-Phylum - - - Echinodermata. 

 Glass Asteroidea. 



Fig. 89. — AsTERiAS Rubens x \. 



On the left the oral surface is seen with the five ambulacral grooves and 



tube-feet ; on the right is the aboral surface with the madreporite 



between the two lower arms. 



Asterias rubens (the starfish) is one of the commonest 



marine httoral animals. The body is of a dull yellow-red 



colour, flattened and produced into five equal-sized arms. 



External "^^^^ gives an external appearance of axial 



_ . symmetry, but it will be seen that it is really 



Features. \ \ ^' ^ . „ . , . . -^ 



^plano-symmetric. For purposes of description, 



the five axes of the arms are termed radii and the five 



radii between them are called the inter-radii. In the 



