TAXONOMY 273 



Class ARCHIANNELIDA. Marine Annelida with no setse nor parapodia. 



Class CHjETOPODA. Annelida with setse and a perivisceral coelom; marine, 

 freshwater, or terrestrial in habitat. Earthworms. 



Class HIRUDINEA. Annelida without setae, and with anterior and posterior 

 suckers. Leeches. 



Phylum MOLLUSCA. Triploblastic, bilaterally symmetrical l^symmetry often 

 obscured) unsegmented animals with a coelom, a muscular foot and usually a shell. 

 Mollusks. 



Class AMPHINEURA. MoUusca with obvious bilateral symmetry, sometimes an 

 eight-parted calcareous shell and several pairs of gills. 



Class GASTROPODA. Mollusks with a head and with bilateral symmetry usu- 

 ally obscured by a spiral shell of one piece. Snails. 



Class SCAPHOPODA. Mollusca with conical tubular shell and mantle. 



Class PELECYPODA. Mollusks without a head, with bilateral symmetry, a 

 shell of two lateral valves and a mantle of two lobes. Clams, mussels. 



Class CEPHALOPODA. Mollusks with distinct bilateral symmetry and a foot 

 bearing eyes and chvided into arms usually with slickers. Cuttlefishes, octopods. 



Phylum ARTHROPODA. Triploblastic, bilaterally symmetrical, segmented 

 animals with usually more or less dissimilar somites, a coelom verj^ much reduced, 

 paired jointed appendages, and chitinous exoskeleton. 



Class CRUSTACEA. Arthropods breathing by means of gills, two pairs of an- 

 tennae. Crayfishes, crabs and shrimps. (Figs. 241, 242.) 



Class ONYCHOPHORA. Primitive air breathing arthropods with tracheae and 

 nephridia. Peripatus. 



Class MYRIAPODA. Arthropods with tracheae, one pair of antennae and many 

 similar legs. Centipedes and millipedes. 



Class INSECTA. Arthropods with tracheae, one pair of antennae and three 

 pairs of legs. Insects. (Figs. 186, 236.). 



Class ARACHNIDA. Arthropods with tracheae, book lungs or book gills and no 

 antennae. Spiders. 



" Phylum CHORDATA. Animals having at some stage a skeletal axis (the noto- 

 chord), gill slits in embryo or adult, and a nerve cord dorsal to the alimentary canal. 



Subphylum ENTEROPNEUSTA. Worm-like chordates of somewhat doubtful 

 systematic position. 



Subphylum TUNICATA. Sac-like marine animals with a cuticular outer covering 

 known as a tunic or test. Tunicates. (Figs. 69, 70.) 



Subphylum CEPHALOCHORDA. Fish-like chordates with a permanent noto- 

 chord composed of vacuolated cells. Amphioxus. 



Subphylum VERTEBRATA. Chordates in which the notochord either persists 

 or becomes invested by cartilage, segmented, to form a vertebral column, or disap- 

 pears, the vertebral column being made up of bony segments. (Figs. 103-107, 

 152-157.) 



Class CYCLOSTOMATA. Eel-like vertebrates without functional jaws or lateral 

 appendages. Lampreys and hagfishes. 



Class ELASMOBRANCHII. Fish-like vertebrates without air bladder, with jaws, 

 and with a cartilaginous skeleton and placoid scales. Sharks, rays and skates. 

 (Fig. 150.) 



Class PISCES. Aquatic, cold-blooded vertebrates breathing by means of gills, 

 with air bladder, a two chambered heart, and usually a dermal exoskeleton of scales. 

 Fishes. (Fig. 155.) 



Subclass TELEOSTOMI. Fishes with a skeleton consisting wholly or partially 

 of bone, breathing by means of gills. True fishes. 



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