52 COMMUNITY FUNCTIONS— DYNAMICS OF BIOTIC FORMATION 



where they are not to be found. The limited character of the simi- 

 larity has already been pointed out (p. 34) in connection with a 

 comparison of "zoophytes" and land plants. In a bio-ecological treat- 

 ment, it becomes important to know that the animals of these climatic 

 communities display comparable behavior and physiological charac- 

 ters but lack unity of life-form characters. On the other hand, marine 

 animals may show segregation of characteristic life forms in some 

 communities. 



Zoophytes have included chiefly the larger upright, treelike delicate 

 corals, but they may well comprise also the more massive corals with 

 similar branching. The life forms of the notably large species include 

 tree forms with radial symmetry, or more rarely fan forms, produced 

 by branching in one plane, like plants of the genus Arcca. On these 

 the zooids are arranged much like leaves, but have a greater tendency 

 to cover the trunk and main branches. A few whip forms have the 

 zooids radially arranged about the trunk like the flowers of the mullein 

 {Verbascum thapsus) . These rigid plantlike animals are typical in 

 warm seas where corals play an important role in the biotic commu- 

 nities. Their life forms probably have value in characterizing these 

 communities, but no studies from this viewpoint are at present known. 



In addition to the large rigid forms, there are many small delicate 

 hydroids and bryozoans that exhibit the same types of branching and 

 zooid arrangement. The life-form peculiarities of these are usually 

 the taxonomic characters of orders, families, genera, or species. They 

 are apparently of little significance in marine communities, playing a 

 role somewhat similar to that of cup fungi and lichens in a forest. 

 There are also sessile multiple-individual animals that assume an 

 essentially spherical form about a foreign body as an axis (Pectina- 

 tella). Some others approach spherical form, though the body rests 

 upon a substratum; of these the sponges, especially the commercial 

 types (Moore, 1908), are examples. A few compound tunicates as- 

 sume a nearly spherical form, Macroclinum pomum of the North At- 

 lantic being an example. Some of the massive corals are essentially 

 similar, and on the whole a number of community dominants are 

 included in this type. 



Some of the decumbent animals form fans on the substratum; 

 others make simple plates. Still others are amorphous lumps and 

 irregular aggregations owing in some cases to natural and presumably 

 hereditary tendencies, which would classify them as life forms (Shel- 

 ford, 1914, d). This brief statement concerning the life forms and 

 growth forms of aquatic sessile and sedentary animals by no means 

 exhausts the field either as to detail or types, but it does show that 



