right to stand in the ranks of animals. This was after 

 the last skeptics had been satisfied that sponges could 

 feed like any animal without having to move about 

 to gather their food. "The poor creatures," wrote one 

 naturalist, "receive their nourishment from the wave 

 that washes past them; they inhale and respire the 

 bitter water all their lives." He could have saved his 

 sympathy, because sponges were enjoying great 

 prosperity at least half a billion years before man 

 appeared on the scene. Vaselike fossil glass sponges 

 and masses of fossil glass needles from the support- 

 ing framework of such sponges are found in the ear- 

 liest fossil-bearing rocks we know. 



An elaborate skeletal framework permeating the 

 entire body is very important to an animal in which 

 gelatinous material holds together loosely organized 

 masses of delicate cells which must be firmly sup- 

 ported to keep the extensive network of canals and 

 chambers from collapsing and so interfering with the 

 vital circulation. Yet every group has its exceptions, 

 and there are a few sponges without skeletons. The 

 soft elastic framework of the bath sponge and its rel- 

 atives makes these few aberrant forms useful to us, 

 but such support without hard particles in addition 

 is rare among all the thousands of kinds of sponges. 

 Most are much too hard and scratchy, too brittle or 

 friable, whether alive, dead, or skeletonized, to be of 

 much use to man. Their bodies are usually thor- 

 oughly permeated with microscopic hard particles, or 

 spicules, which either are simple needles or have a 

 number of rays in a variety of configurations. In one 

 class the spicules are calcareous, or chalky, but in 

 most sponges the spicules are siliceous and like mi- 

 nute splinters of glass. If a fibrous network is present, 

 it is usually combined with hard spicules. Those 

 sponges in which long spicules protrude from the 

 surface are quite bristly. As if to make doubly sure 

 that no animal will be attracted to their flesh, many 

 sponges have noxious odors. Little wonder, then, that 

 sponges have so few enemies and that the bodies of 

 the less compact forms give shelter to many hundreds 

 of kinds of invertebrates, especially crustaceans and 

 worms, and even to fishes. Among the few animals 

 definitely known to feed on sponges are certain sea 

 slugs (nudibranchs), limpets, and periwinkles — all 

 of them mollusks. But perhaps there are others. 



The known number of sponge species has been 

 estimated as high as 4500, but of these only about 

 150 species, all members of the family Spongillidae, 

 live in fresh waters. The rest are marine, and these 

 grow most abundantly in warm shallow seas but are 

 widely distributed also in temperate and cold waters 

 and at all depths. During the Galathea expedition 

 sponges were recorded from the sea bottom at nearly 

 21.000 feet below the surface. Fibrous sponges pre- 

 dominate in shallow tropical waters but give way to 

 calcareous and siliceous sponges in cold water. The 



glass sponges (p. 60) are deep-water forms. The 

 favored substrate is rocky or hard bottom along the 

 seashores or in coral-reef lagoons, though some 

 sponges are found encrusting pilings, shells, or even 

 the backs of certain crabs (Plate 2). A few forms lie 

 free at the bottom, but all the rest are firmly secured 

 in some way, either fastened to a solid object or on 

 muddy bottom anchored by a long tuft of glassy 

 spicules. An occasional hardy species, like Tetilla 

 mutabilis, which lives in the mud flats of estuaries 

 in southern California, can somehow manage to sur- 

 vive the temperature changes, pollution, and sus- 

 pended sediments of such a habitat. But sponges as 

 a group are especially vulnerable to suspended par- 

 ticles that could clog their labyrinthine channels; and 

 they grow best in very clear waters, thriving on mud 

 bottoms only in deep or very quiet waters where the 

 mud is seldom or never in suspension. 



The sizes and shapes of sponges vary from minute 

 urns only a fraction of an inch long to erect vaselike 

 or branching types 5 or 6 feet tall, or broad, squat, 

 irregular or rounded masses big enough for several 

 people to sit on. The simpler and smaller sponges are 

 often radially symmetrical cylinders or vases, fas- 

 tened at the lower end, with a single large opening 

 at the top. But most sponges are colonial and have no 

 special symmetry. They continue to spread out in- 

 definitely in a plantlike manner and with little indi- 

 viduality. If a single vent with its contributory chan- 

 nels represents an individual in the diffuse colony, 

 then it is difficult indeed to tell where one individual 

 stops and the next one begins. Over long periods 

 sponge colonies do change their patterns on rocks, 

 almost as if they were moving about, by a constant 

 reorganization of the cells around the periphery. As 

 they meet other colonies of the same species they co- 

 alesce. The most common shapes are irregularly mas- 

 sive, encrusting, or branching, and the many large 

 excurrent openings may be on the tips of branches or 

 elevated cones, or sunk into craters. The same species 

 may grow erect branches in quiet waters and cling 

 matlike, molded to the substrate, where the surf is 

 strong. In fresh waters and on temperate rocky 

 shores encrusting sponges are most common. After 

 a storm a beach may be strewn with decaying sponge 

 fragments torn from the rocks, or with sponge-cov- 

 ered mollusk shells hurled in from offshore bottoms. 

 On a beach in Panama we once saw hundreds of 

 empty scallop shells cast up by a storm, and every 

 one bore a finger-like sponge several inches tall. The 

 finger-like, vaselike, and fanlike sponges are charac- 

 teristic of warm, quiet seas or of the deep ocean bot- 

 tom. In such quiet-water habitats many sponges 

 have fairly regular growth forms, and in more elegant 

 times than ours they were given common names like 

 the fan, the trumpet, the bell, the lyre, the peacock's 

 tail, Neptune's goblet, the sailor's nest, the feather, 



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