CHIEF DIVISIONS OF THE ANIMAL KINGDOM. 47 



Order 4. Ophiuroidea (Brittle-stars) Ex. Sand-stars (Ophiura), 



Brittle-stars (Ophiocoma). 



Order 5. Asteroidea (Star-fishes). Ex. Cross-fish (Uraster), Sun- 

 star (Solaster), Cushion-star (Goniaster). 

 Order 6. Echinoidea (Sea-urchins). Ex. Sea -eggs (Echinus), 



Heart-urchins (Spatangus). 

 Order 7. Holothuroidea (Sea-cucumbers). Ex. Trepangs (Holo- 



thuria). 



B. SCOLECIDA. Body usually flattened, or cylindrical and worm-like ; 

 integument soft, without lime. Water-vascular system not assisting in 

 locomotion. Nervous system consisting of one or two ganglia or little 

 masses, and not disposed in a radiate manner. 



Order I. Tteniada. Ex. Tape-worm (Tsenia). 



Order 2. Trematoda (Suctorial worms). Ex. Liver-fluke (Dis- 



toma). 

 Order 3. Turbellaria. Ex. Planarians (Planaria), Ribbon-worms 



(Nemertes). 

 Orders Acanthocephala (Thorn-headed worms). Ex. Echino- 



rhynchus. 



Order 5. Gordiacea (Hair-worms). Ex. Gordius. 

 Order 6. Nematoda (Thread- worms). Ex. Round- worm (Ascaris), 



Guinea-worm (Filaria), Vinegar-eel (Anguillula) . 

 Order 7. Rotifera (Wheel-animalcules). Ex. Builder-animalcule 



(Melicerta), Flexible Creeper (Notommata). 



SUB-KINGDOM IV.ANNULOSA. 



Animal composed of numerous definite segments or " somites," arranged 

 longitudinally, one behind the other. Nervous system always present, con- 

 sisting typically of a double chain of nervous masses, or ganglia, which are 

 placed along the lower surface of the body, and form a collar around the 

 gullet. Limbs (when present) turned toward that side of the body on 

 which the main masses of the nervous system are situated. 



DIVISION A. ANARTHROPODA. Locomotive appendages, when pre- 

 sent, not distinctly jointed or articulated to the body. 

 CLASS I. GEPHYREA. Ex. Spoon-worms (Sipunculus). 

 CLASS II. ANNELIDA (Ringed-worms). 



Order I. Hirudinea. Ex. Leeches (Sanguisuga, Hirudo). 

 Order 2. Oligochata. Ex. Earth-worms (Lumbricus), Water- 

 worms (Nais). 



Order 3. Tubicola. Ex. Tube-worms (Serpula). 

 Order 4. Errantia. Ex. Sand-worms and Sea-centipedes (Nereis), 



Lob-worm (Arenicola), Sea-mouse (Aphrodite). 

 CLASS III. CH^TOGNATHA (Arrow- worms). Ex. Sagitta. 

 DIVISION B. ARTHROPODA. Locomotive appendages jointed or articu- 

 lated to the body. 



CLASS I. CRUSTACEA. Respiration aquatic, mostly by gills. Two 

 pairs of antennae. Limbs more than four pairs in number, carried upon the 

 thorax, and generally the abdomen also. 



Order I. Ichthyophthira. Ex. Lernsea. 



Order 2. Rhizocephala. Ex. Peltogaster. 



Order 3. Cirripedia. Ex. Barnacles (Lepas), Acorn-shells (Bal- 



anus). 



Order 4. Ostracoda. Ex. Water-fleas (Cypris). 

 Order 5. Copepoda. Ex. Cyclops. 

 Order 6. Cladocera. Ex. Branched-horned Water-fleas (Daphnia). 



