THE INVERTEBRATE LEGIONS 



107 



ROT ITER 

 Qrea+ly enlarged 



Bird's hcad bkyozoam 



8u.<^u.la.- 2. in 



ENCRUSTING BRYOZOflN 

 £Q.ch OLniroal - li^ in. 



Ffg. 34. Rotifer and hryozoans. Adapted from several authors. 



either hornv and flexible or heavily calcified and stiff. Bryozoans feed by filter- 

 ing plankton out of sea water by means of a crown of tentacles called a 

 "lophophore." 



The bird's head bryozoan, Biigula, is a common and very widespread form 

 found in most waters of the world. It looks like a small brownish tuft of moss, 

 is 2 to 3 inches high, and grows anchored to almost any hard bottom in shallow 

 water. Some individuals of the colony are reduced in size and look very much 

 like the head and beak of a bird. These are called "avicularia" and constantly 

 move from side to side snapping at any object that lands on the colony, keeping 

 the colony free of foreign matter. Living BuguJa seen under a microscope show 

 these amusing little individuals very well. 



An amazing habit of manv moss animals is the formation of the brown bodv. 

 Periodically, the tentacles and anterior digestive system of a single animal 

 degenerate into a brown clump which is ejected through the anus. Then a new 

 set of internal organs is regenerated. No reason for this is known. The brvozoa 

 lack a circulatorv svstem, and their evolutionary position in the animal kingdom 

 is not known. 



PHORONID WORMS: Phylum Phoronida— F/^wr^ 33 



The genus Phoronis with a very few species comprises almost all of this 

 phylum. These worms are small, usually about a half-inch in length, and are 

 like moss animals in habits and appearance except that they are adapted to live 

 in straight tubes in shallow mud or sand flats rather than attached to hard 

 substrate. Also, they are not colonial, although they are frequently found grouped 

 together. They have a tentacle tuft (lophophore) and filter plankton from sea 

 water as do moss animals. While they are not common on the east coast, thev 

 are fairly abundant on the west coast. 



SEGMENTED WORMS: Phylum Annelida 



The worms whose bodies are divided into segments are called "annelida" 

 which means "ringed." In some of these worms, like the sandworm. Nereis, 

 the rings, or segments, are obvious, but in others they are less so. This is a 

 huge group of several thousands of species. Segmented worms are evolutionarilv 



