TYPICAL SPONGES IN THE MUSEUM. 



A. CALCAREOUS SPONGES (CLASS CALCAREA) 



The most conspicuous characteristic of this class is the 

 calcareous or carbonate of lime skeleton. The class is divided 

 into two groups, the first containing those sponges whose hollow 

 interior (paragastric cavity) is entirely lined with "collared cells" 

 (order Homocoelida) , the second comprising those in which 

 the "coUared cells" are confined to thimble-like prolongations of 

 the paragastric cavity (order Heterocoelida) . 



An example of the Homocoelida is the Ascon sponge Leuco- 

 solenia primordialis Hackel. The genus to which this species 

 belongs is found in all seas to a depth of 6000 feet. Its manner 

 of growth varies from solitary, erect, cylindrical sponges to 

 encrusting colonies of serpent-like tubes ramifying in a compli- 

 cated network. Sometimes the whole colony assumes an erect 

 vase-like form with walls made up of entwining tube-like in- 

 dividuals. The sponge on exhibition is of the encrusting type, 

 growing in this instance on a colony of barnacles. 



The Sycon sponge, Grantia ciliata Fleming, represents in the 

 exhibition the order Heterocoelida. This is a common species 

 foimd all along the New England sea-coast. It is a small tubular 

 sac with the osculum surroimded by a circle of finger-like spicules, 

 as shown in the illustration on page 224. It grows from an inch 

 to an inch and a half in length, in small cluster-like colonies 

 attached to sea-weed, submerged timbers, shells, etc. The 

 specimens in the glass jar are growing on a mussel shell which 

 is also partly encrusted with small star-shaped colonies of the 

 interesting Ascidian, Botryllus. 



B. THE NON-CALCAREOUS SPONGES (CLASS NON-CALCAREA). 



The sponges of this class have no traces of carbonate of lime 

 in their skeletons. Instead some contain silicious spicules 



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