A cluster of calcareous sponges, pulled from their 

 attachment on wharf piling. Three vaselike ones at 

 left are St/con coronatum, about 1 inch long. Much- 

 branched mass at right is Leucosolenia complicata. 

 (England. D. P. Wilson) 



names. Widely distributed on rocky shores near low- 

 tide mark, they favor well-aerated spots where the 

 water is in motion without being really surfy. Leuco- 

 solenia grows only in colonies of little vertical tubes 

 connected by horizontal tubes or by a complex net- 

 work of branching tubes. An upright branch encloses 

 a single cavity, completely lined with flagellated, col- 

 lared feeding cells, and opening at the top by a single 

 vent. The colonies spread in tide pools or over the 

 underside of stones as small fungus-like patches 

 about Vi of an inch high. Or they hang as bushy 

 growths, which have been compared to miniature 

 bunches of bananas, from wooden wharf pilings or 

 from the stems of the brown seaweed Fucus. One 



species, in which the tubes are compacted into an 

 encrusting meshwork of twisted tubes, may be yel- 

 lowish, pink, red, brown, or bluish gray. The colonies 

 are somewhat stiff, because the fragile structure of 

 nonliving gelatinous matrix and delicate living cells 

 is strengthened and supported throughout by both 

 scattered and interlacing spicules. 



The urn sponge, Sycon. is also called the crowned 

 sponge, because the fringe of giant needles that rims 

 the constricted opening at the top of the urn looks 

 like a little crown. In one species from deeper wa- 

 ters the fringe is as long as the body itself. Crowned 

 sponges have a more complex internal structure than 

 do the little sacs of the Leucosolenia colony, but ex- 

 ternally most species display a simpler growth form. 

 The single cylindrical individuals, dull gray or yel- 

 lowish, and usually about 1 inch in length, spring in 

 small clusters from a single attachment. These are 

 widely distributed, but they are best known on north- 

 ern Atlantic shores. A colonial species with finger- 

 like branches is an inhabitant of southern seas. They 

 flourish where wave action is not too strong, and at 

 low tide can be seen in tide pools, under stones, and 

 hanging from wharf pilings or from the brown sea- 

 weed Fucus or the green eelgrass Zostera. 



The purse sponge, Grantia. is named for R. E. 

 Grant, who first really understood the structure and 

 workings of sponges, gave them their phylum name, 

 and cleared up the uncertainties about their status as 

 animals. Now his work is recalled whenever we refer 

 to the light gray or creamy white sponges that hang 

 as little bags with the somewhat compressed opening 

 down, and when the tide is out collapse to flattened 

 purses. So abundant on certain English beaches as to 

 occur by the tens of thousands in a few hundred 

 yards, they hang in rocky crevices, or among the 

 delicate red algae that droop from rock overhangs, 

 or from the blades of eelgrass. Each is usually about 

 1 inch long; but D. P. Wilson, writing of Grantia 

 compressa in They Live in the Sea. says that in Eng- 

 lish harbors where food is plentiful and wave action 

 subdued the flattened sponges may be almost as 

 large as one's hand. They are rarely the neat little 

 bags drawn in books, but are much folded and 

 twisted upon themselves. The manner in which they 

 split along these folds, dropping fragments that at- 

 tach and grow into new sponges, has been vividly 

 described by Maurice Burton in Margins of the Sea. 



The Glass Sponges 



( Class Hexactinellida ) 



The possession of six-rayed spicules distinguishes 

 the glass sponges from all others. Composed chiefly 

 of silicon dioxide, the spicules show a variety and 



60] 



