MISCELLANEOUS MINOR PHYLA 



167 



Statoblast of 

 Plumaiella 



Lophopfiore 

 Mouth 



Anus 



Infestlne 



Stomach 



Cecum 



Statoblast 



Plumafella 



Figure 88. Phylum Bryozoa. Plumatella, a com- 

 mon fresh-water bryozoan. Below, drawing showing 

 the structure of a single individual (a zooid). En- 

 larged. Above, statoblast of Plumatella. 



"lamp shell" refers to the resemblance of 

 the shells to the oil lamps of the Romans. 

 Within the shell is a conspicuous structure, 

 the lophophore, which consists of t^vo coiled 

 ridges, called arms; these bear ciliated ten- 

 tacles. Food is drawn into the mouth by 

 the lophophore. A true coelom is present, 

 within which lie the stomach, digestive 

 gland, short blind intestine, and the 

 "heart." 



The group Brachiopoda is extremely old, 

 dating since Cambrian time; and, although 

 found in all seas today, brachiopods were 

 formerly more numerous in species and of 



much greater variety in form than at present. 

 Some of them, for example Lingula, are ap- 

 parently the same today as they were in the 

 Ordovician period, estimated at over 400 

 million years ago. Lingula (see headpiece, p. 

 163) is thought to be the oldest animal 

 genus known; it is called a "living fossil" 

 because it has not changed, on the outside 

 at least, during long geologic periods. 



PHYLUM CHAETOGNATHA 

 (ARROW WORMS) 



The Chaetognatha are marine animals 

 which swim about near the surface of the 

 sea (Fig. 89). The best-known genus is 

 Sagitta, the arrow worm. Tlie bilaterally 

 symmetrical body consists of three regions, 

 head, trunk, and tail. Lateral and caudal 

 fins are present. There is a distinct coelom, 

 a digestive tract with mouth, intestine, and 

 anus, a well-developed nervous system, two 

 eyes, and other sensory organs. There are 

 no circulatory, respirator}-, or excretory or- 

 gans. The mouth has a lobe on either side 

 provided with bristles which are used in 

 capturing the minute animals and plants 

 that serve as food. The members of the 

 group are hermaphroditic. Many species are 

 very widely distributed. 



PHYLUM GASTROTRICHA 



To this group belong certain microscopic 

 animals that live in both fresh and salt 

 water and are often abundant among algae 

 and debris upon which they feed. They 

 range in length from 0.06 to 1.5 mm. The 

 gastrotrichs resemble some ciliate protozoans 

 (Fig. 89). The body is indistinctly divided 

 into head, neck, trunk, and toes. The 

 mouth, which is at the anterior end, is sur- 

 rounded by oral bristles; locomotion is ac- 

 complished by longitudinal bands of cilia 

 on the ventral surface. On the dorsal surface 

 there are many slender spines. The intestine 



