3 o3 



LOWER FORMS OF MARINE LIFE 



Echinoderms. 



tide-marks. Nearly allied are the sabellas and serpulas, the former of which make 

 tubes of sand and fragments of shell aggregated into rock-like masses, while the 

 latter secrete stony tubes, from the summits of which are protruded clusters of 

 graceful tentacles. One of the most beautiful is Spallanzani's tube-worm {Spiro- 

 graphis spallanzanii), of the Channel Islands and the Mediterranean, which has 

 an upright spiral tube and unsymmetrical white, violet, or brown gill-plumes. 



Another is the common tube-worm 

 (Serjnda vermicularis) so abundant 

 on oyster, scallop, and other shells. 

 A third type, which lives on sea- 

 weed as well as on shells, is Spiror- 

 bis, in which the tube is coiled into 

 a flat spiral one-eighth of an inch or 

 less in diameter. 



Grouped in an- 

 other sub-kingdom, the 

 Echinodermata, are the starfishes, 

 sea-urchins and their allies. The 

 starfishes of the present day, of 

 which there are at least five hundred 

 species, are cosmopolitan. Among 

 (.hose which inhabit the North 

 Atlantic is the red starfish (Asterias 

 subens), found from within the tide- 

 range to a depth of 50 fathoms. 

 It has five rays, averages about 

 6 inches in diameter, occasionally ex- 

 ceeding 9, and in colour is generally 

 reddish, yellowish, or brownish. As 

 it is destructive to oysters, it is 

 caught in great numbers on the 

 west coast of France, where it 

 is used as manure. A starfish 

 distinguished by its size, which 

 sometimes approaches 18 inches in 

 diameter, and by living at a depth 

 of from 10 to 100 fathoms in the Mediterranean, and all around the British Isles, 

 from which the preceding species is absent, is the orange comb-star (Astropecten 

 aurantiacus), which on both sides of its five arms has a row of upper and under 

 edge plates and also has flat spines. Its food-canals terminate blindly. 



The brittle stars (Ophiuroidea) differ from the sea-stars chiefly in the pos- 

 session of a central disc, sharply defined from the arms, and in other features. They 

 crawl chiefly by means of their arms, which wind about in so snaky a fashion that 

 the animals are frequently called snake-stars in consequence. In many species 

 they can be turned upwards, and are very strong and branched, as is the 

 case with the tree-shaped Medusa's head Gorgonocephalus arborescens of the 



POSTOLE STAR. 



