THE INVERTEBRATE LEGIONS 



91 



Sponges exist in a wide variety of shapes. Some are small and even parasitic. 

 Others, such as the Pacific Neptune's cup, Poterion, are big enough to sit in. 

 In general, sponges are like plants in growth pattern. For instance, a tree has 

 a pattern of growth by which it may be recognized, but there is no set number 

 of branches it must have. The same is true of sponges in that there are branching, 

 erect, encrusting, or vaselike patterns of form, but each species shows consider- 

 able variation within that form. 



The great majority of sponges are marine, there being only one small 

 fresh-water group. Sponges are largest and most varied in shallow, tropical 

 waters. Almost everywhere that they are found, a host of other animals, mostly 

 worms and crustaceans, are associated with them, living in the cavities for 

 protection. The most notable of the sponge symbiotic relationships exist 

 between several species of hermit crabs and a few species of a family of horny 

 sponges. The sponge grows on the shell occupied by a crab and eventually 

 grows to cover the entire shell. Then the sponge dissolves the shell away and 

 itself forms the home of the hermit crab. This is a case of mutualism in which 

 the crab is protected from predators by the bad taste of the sponge and the 

 sponge benefits by receiving transportation. Although most sponges taste and 

 smell badly and are protected by their sharp spicules, two groups of animals, 

 the nudibranch molluscs or sea slugs and the sea spiders, have some species that 

 eat sponges. The sea slugs frequently imitate sponges in shape and color. The 

 sea spiders suck the juices of sponges. 



Calcareous Sponges : Class Calcarea — Figure 24 



These are the simplest sponges, small and vaselike, either single or grouped 

 in colonies, yellowish to whitish or muddy in color, and with spicules of lime. 



VENUS FLOWER BASKET 

 Euplec+ella-lOin. 



BREAD-CRUMB SPOMGE 

 Halichror,dr,o.-(nficih+4in- 



BATH SPONGE 

 Eu-sponc^ia- 8in. 



Fig. 24. Sfonges. Drawn from life. 



