100 



COLLEGE ZOOLOGY 



line of development, of more complex ani- 

 mals (Fig. 430). 



RELATIONS OF PORIFERA TO 

 MAN AND OTHER ANIMALS 



Sponges are mostly beneficial to man. 

 They supply him with the sponges of com- 

 merce, which are the spongin skeletons of 

 certain species living chiefly near the shore 

 of the Mediterranean Sea, the coast of Aus- 

 tralia, the Bahama Islands, Cuba, and 

 Florida. Only the eastern Mediterranean is 

 superior as a sponge-producing region to 

 that around Florida. 



Sponge culture, that is, growing sponges 

 from cuttings, is little practiced today, due 

 to the difficulties in preventing theft of the 

 crop. Fishing for sponges is carried on by 

 divers either with or without a diving suit; 

 the latter are known as skin divers. Com- 

 mercial diving for sponges is dangerous be- 

 cause most of the shallow waters have been 

 "fished out" and the deeper regions must be 

 worked; these often cause the divers to suf- 

 fer from a pressure disease called the bends. 

 Sharks are another danger to the diver. 

 There is a good market for the natural 

 sponge, although it must compete with the 

 cellulose and rubber substitutes. 



Bath sponges in their living state resem- 

 ble internally a piece of raw beef liver in 

 both consistency and color. Externally they 

 are black or blackish in color. 



Boring sponges occur in shallow water 

 near shores all over the world. They form ir- 

 regular masses and are a bright sulfur yel- 

 low in color. Their name has reference to 

 their habit of attaching themselves to the 

 shells of oysters, clams, etc., and boring 

 them so full of holes that the animals within 

 are killed and in time the shells are en- 

 tirely broken up. 



Some sponges are poisonous; certain forms 

 are as dangerous as poison ivy, when touched 

 by man, and produce similar results. Other 

 sponges when alive give off a strong unpleas- 



ant odor, and many contain sharp spiny 

 spicules. Probably for these reasons as well 

 as for purposes of concealment, certain spe- 

 cies of crabs place sponges on their backs 

 or on their legs. Other animals find the 

 body of the sponge an excellent place in 

 which to retreat for protection. 



Of ornamental interest is a sponge known 

 as Venus's-flower-basket, which builds up a 

 beautiful skeleton of "spun glass" in the 

 form of a cylinder about a foot long. Sponges 

 of this type live in the sea, where they are 

 fastened in the mud of the sea bottom by a 

 mass of long threads at one end. 



Some sponges are of economic importance 

 in that the siliceous spicules form large flint 

 deposits. 



CLASSIFICATION OF 

 THE PORIFERA 



{For reference purposes only) 



Sponges are all sessile animals in the adult 

 stage, and asymmetrical or radially symmetrical 

 in form. Their many cells are loosely arranged 

 into two, more or less definite, layers, between 

 which are amoeboid wandering cells. Neither 

 organs nor mouth is present, the cells acting 

 mostly independently. The soft tissues of 

 sponges are usually held in place by skeletons 

 of spicules or spongin. The bodies of sponges 

 contain pores, canals, chambers, and a central 

 cavity, through which currents of water flow. 

 Collar cells, the choanocytes, line some of the 

 body cavities. The 5000 or more living species 

 of sponges are marine, except for about 150 

 species which comprise the fresh-water family 

 Spongillidae (Fig. 45). Three classes and 12 

 orders are recognized as follows: 



Class 1. Calcispongiae. Shallow-water species, 

 comparatively simple in structure. 

 Calcareous spicules make up the prin- 

 cipal skeleton. Ascon, sycon, and 

 simple rhagon types are present. 

 Order 1. Asconosa. Sponges of ascon 

 type, or ascon t}'pe at first, 

 changing directly into rhagon. 

 Ex. Leucosolenia (Fig. 46). 



