68 PLANT AND ANIMAL CLASSIFICATION 



Exercises XII and XIII 



ate symmetry in adults; most forms with 

 spiny skin; triploblastic with large coelom 

 and distinct ahmentary canal; calcareous 

 plates provide protective exoskeleton; tube 

 feet for locomotion. 



11. PHYLUM MOLLUSCA (L. moUuSCUS, Soft). 



Chitons, snails, slugs, whelks, clams, scal- 

 lops, oysters, ship worms, squids, octopuses. 

 Unsegmented; appendages not jointed; usu- 

 ally a shell and mantle; "foot" usually 

 present. 



(ii) Segmented 



12. PHYLUM ANNELIDA (L. annelus, a little 

 ring). Segmented worms such as earth- 

 worms, marine worms, leeches. Blood ves- 

 sels, excretory organs, and nervous system 

 segmentally arranged; distinct coelom; ven- 

 tral double nerve cord of "ladder type"; 

 appendages not jointed. 



13. PHYLUM ARTHROPODA (Gr. arthron,]omi\ 

 podos, foot). Crustaceans such as crayfish, 

 water fleas, crabs, barnacles; centipedes, 

 millipedes; insects; spiders, mites, ticks, 



scorpions. Segmented (but body cavity is 

 continuous and without transverse septa; 

 segmentation shown internally in arrange- 

 ment of organs); groups of segments tend 

 to fuse into larger regions (head, thorax and 

 abdomen); paired, jointed appendages; exo- 

 skeleton; nervous system of "ladder type"; 

 main longitudinal blood vessel dorsal to 

 alimentary canal. 



14. PHYLUM CHORDATA (Gr. chorde, cord). 

 Internal skeleton with a notochord sometime 

 during life history; gill clefts in throat some- 

 time during life history; central nervous 

 system is tubular and dorsal. The phylum 

 Chordata consists of several subphyla, the 

 most important of which is the Craniata (or 

 Vertebrata), the backboned animals. Among 

 the members of the subphylum are the 

 Cyclostomata (lampreys and hagfishes), 

 the Elasmobranchii (sharks and rays), Pisces 

 (bony fish). Amphibia (salamanders, frogs 

 and toads), Reptiha (lizards, snakes, turtles, 

 crocodiles), Aves (birds), and Mammaha 

 (mammals). 



EQUIPMENT 



Laboratory exhibit of plants and animals representing all major groups, labeled and unlabeled 



