120 LABORATORY STUDIES IN ZOOLOGY 



upon the surface of gelatinous masses 



Phylum Molluscoida 

 GG. Calcareous shells present which may be spiral or of two 

 valves lateral in position or segmented and placed on 

 back. If sliell appears to be absent the body is elongate 

 with a "saddle-blanket" patch on the back or the head 

 bears a pair of eyes and long tentacles al)out the mouth 

 each tipped with cuplike adhesive organs 



Phylum Mollusca 

 FF. True metamerism obvious. 



G. Without jointed locomotor appendages 



Phylum Annelida 

 H. Segments bearing parapodia or lateral bristles or both 



Class Choetopoda 

 HH. Without either parapodia or bristles. 



I. Tentacles present Class Archianellida 



II. Adhesive organ at either end of body, tentacles 



absent Class Hirudinea 



GG. Jointed locomotor appendages present 



Phylum Arthropoda 

 H. Antenna; present. 



I. Antenna; two pairs; gills present. . . .Class Crustacea 

 II. Antenna; one pair. 



J. Most body segments bearing similar jointed leg- 

 like appendages. Abdomen not differentiated 



Class Myriapoda 



JJ. Abdomen differentiated and without locomotor 



appendages. Thorax with three pairs of walking 



legs. Usuall}^ two (sometimes one) pairs of wings 



present Class Insecta 



HH. Antenna^ absent or apparently so; head and thorax 

 combined, equipped for aerial respiration 



Class Arachnida 

 DD. Skeleton internal, metamerism obvious in some, subdued in 

 others. Axial skeleton in form of notochord or vertebral 

 column of cartilage or bone or both. Pharynx with gill slits 



Phylum Chordata 

 E. Locomotor appendages absent. 



F. Body wormlike with proboscis, collar, and evident gill slits 

 or (in some exotic forms) polyp-like with tentacles at free 

 end. Notochord confined to proboscis 



Subphylum Hemichorda 

 FF. Body sachke; inhalant and exhalant apertures; with or 

 without peduncle (stalk), single or colonial in habit 



Sybphyluni Urochorda 



EE. Locomotor appendages present in form of mesal or paired fins 



or both, or as legs. 



F. Notochord serving as axial skeleton, continuous mesal 



finfold present Subphylum Cephalochorda 



