114 INVEBTEBUATE MORPHOLOGY. 



sponding to the mesenteries. Usually but a single tentacle 

 communicates with each space, but in some forms a series 

 may arise on the roof of each space so that the tentacles have 

 a radiating arrangement (Discosoma) or may appear to be 

 irregularly scattered, as iu some corals {Fungid). They are 

 usually simple in form, though they may be in some cases 

 pinnate {Phymanthus, Thalassianthus) or even branched. 

 The order is usually divided into two suborders : 



1. Suborder Malacodermata. 



This includes the Sea-anemones or Actinians, all simple 

 forms, not producing colonies, and usually attached by an 

 adhesive base. They never form a skeleton of any kind, 

 though they may develop an enveloping cuticle, usually very 

 thin and in some cases encrusted with foreign matter ; this 

 is more especially the case with deep-water forms, the shallow- 

 water forms, such as Metridium, Hunodes, etc., lacking a 

 cuticle. Many forms possess the power of division, the in- 

 dividuals so produced separating completely and not forming 

 colonies ; furthermore some forms reproduce non-sexually by 

 separating off portions of the tissue at the margin of the base, 

 each portion eventually developing into an adult Actinian. 



3. Suborder Sclerodermata. 



This suborder includes the ordinary corals, which secrete 

 a calcareous skeleton of the character already described 

 (p. 107). A few forms are simple, but the majority produce 

 complex colonies by longitudinal division and by budding, 

 while in others the division is only carried to the extent of 

 the formation of an individual with a number of mouths, as in 

 Fungia and Manicina. In most of the forms the corallum is 

 tolerably dense and may be either branching, as in Ocvlina, or 

 form massive blocks, as the Brain-stone Coral {Ma'andrina), 

 but in Madrepora it is more or less porous. 



The Corals are most abundant in tropical seas and in shallower water, 

 the Madrepores forming under such couditious large reefs, in the lagoons 

 of which the Fungias, Manicinas, and Mseandrinas are found. In colder seas 

 but few forms (Astrangia) are found in shallow water, but in the greater 



