364 INVERTEBRATE MORPHOLOGY. 



1. Order Solenogastres. Shell represented by scattered calcareous 



spicules. Neomenia, Proneornenia, Chcetodenna, Dondersia. 



2. Order Polyplacophora. Shell formed by eight plates on dorsal 



surface of body. Chiton, Trachydermon, Chitonellus. 

 II. Class GASTEROPODA. Visceral hunip usually well developed; body 

 asymmetrical; shell univalved and usually spirally coiled, some- 

 times absent; anus not terminal. 



1. Order Prosobrancliia. Ctenidia present, situated in front of the 



heart; auricle in front of ventricle; mantle edge not fused with 

 body. 



Heart with two auricles; two nephridia (Diotocardia). Haliotis, 

 Turbo, Troehus, Neritina, Pleurotomaria, Fissurella, Patella, 

 Acmcea. 



Heart with a single auricle and a single nephridium (Monotocar- 

 dia). 

 Dentition taenioglossate. 



With creeping habit. Cyprcea, Paludina, Natica, Ampul- 



laria, Littorina, Cydostoma, Calyptrcea, Strombus. 

 With pelagic habit (Heteropoda). Atalanta, Carinaria, 



Pterotracliea. 



Dentition ptenoglossate. lanthina, Scalaria, Solarium. 

 Dentition rachiglossate. Fusus, Buccinum, Nassa, Murex, 



Pttrpura, Olivet,, Marginella. 

 Dentition toxiglossate. Terebra, Conus, Pleurotoma. 



2. Order Opisthobranchia. Ctenidia frequently absent, when pres- 



ent behind the heart; auricle behind ventricle; mantle when 



present not fused by its edges to body- wall; shell frequently 



absent. 

 Mantle present ( Tectibrancliia) . 



Foot with broad flat sole; with creeping habit. Bulla, Janus, 

 Aplysia, PUurobranchus. 



Foot with winglike parapodia, pelagic (Pteropoda). 



Wi th shell (Thecosomata). Limacina, Styliola, Cymbuiiopsis, 

 Without shell (Gymnosomata). Pneumoderma, Clione. 

 Mantle not developed (Nudibramhia). PlKurophyllidia, Phyl- 



ItrJtoe, Limapontia, Doris, JEolis, FaceUina. 



3. Order Ptdmonata. Ctenidia wanting; mantle fused by its edges 



to body- wall; terrestrial or aquatic. 

 Eyes at base of tentacles (Basommatophord). Limncza, Physa, 



Planorbis. 

 Eyes at tip of tentacles (Stylomniatophord). Helix, Limax, Arion, 



Vayinula, Daudebardia, Onchidium. 



III. Class SCAPHOPODA. Visceral hump developed; bilaterally symmetrical; 

 shell cylindrical, open at both ends. Dentalmm, Siphodenta- 

 liiim, Cadnlus. 



